carmel holy word secondary school -...

HKAL Lab oratory report writing exercise Assessing areaA. Objective : State the objective of the experiment.

Exercise : A_1You are asked to perform an experimental for measuring the rate of diffusion of bromine. Tube is first evacuated by connecting via rubber tube to pump. With capsule attached as shown, tap closed, end of capsule broken. Tap opened and time t taken for ‘half-brown’ level to move a certain distance S up tube is measured.Question :What is the objective of this experiment? (1 mark)

AnswerObjective : Measuring the rate of diffusion of bromine. 1A

Exercise : A_2Glass tube is lowered slowly into the beaker of water until the air inside the tube is heard to vibrate loudly (with the frequency of the tuning fork). Then a stationary wave motion of the air in the tube is produced form the superposition of the incident and reflected waves from the air/ water surface.Resonant frequency, f0 = v/4l, where l is the air column length and v velocity of sound. By measuring f0 and l, the velocity of sound in air is found.Question : What is the objective of this experiment? (1 mark)

AnswerObjective : Measuring the velocity of sound in air. 1A

Exercise : A_3With the following setup, an experiment demonstrating the interference of a 3 cm microwave using one microwave transmitter is performed.

Arrange the metal plates such that two slots of approximately 3 cm wide are formed with a separation of about 6 cm. Interference occurs between the two wave-trains diffracted from the two

HKAL Laboratory report writing exercise 1/69

slots that act as two coherent sources. The receiver detects the maxima and minima of the interference pattern as it is moved around. Constructive and destructive interference occur

whenever the path difference of the microwaves from the slots is nλ and respectively.

Question : What is the objective of this experiment? (1 mark)

AnswerObjective : Demonstration of the interference of a 3 cm microwave. 1A

Exercise : A_4You are asked to measure the wavelength of red light using a diffraction grating. The following diagram is the set-up.

Place two metre rules perpendicular to each other as shown. Hold a diffraction grating against one end of a metre rule. View through the grating the vertical filament of the ray-box lamp placed about 1 m from the metre rules. Ask your partner to move a pencil along the second metre rule until it is in line with the middle of the red colour of the first order spectrum. Measure the distance x and hence find sinθ.Question : What is the objective of this experiment? (1 mark)

AnswerObjective : Measurement of the wavelength of red light. 1A

Exercise : A_5The following is the set-up for measuring the capacitance of a parallel-plate air capacitor using a reed switch.



AnswerObjective : Measuring the capacitance of a parallel-plate air capacitor. 1A

Exercise : A_6

or

Set up the above circuit, set the signal generator output to a value, say 3 V, with a measurable current, and increase the frequency stepwise from a low value, say 10 Hz, check whether the output is constant at the previous setting, 3 V, then record the corresponding current readings on the a.c. milliammeter, when frequency increases, the current reading rises and then drops.Question : What is the objective of this experiment? (1 mark)

AnswerObjective : Investigating the current in an LRC series circuit for different frequencies of an a.c.

supply. 1A

Exercise : A_7The diagram below illustrates the basic features of the laboratory apparatus for investigating photoelectricity. It contains a vacuum photoelectric cell P with a photosensitive metal C of large area and a collector of electrons D.



AnswerObjective : Investigation of photoelectricity. 1A

Exercise : A_8You are given some isotopes of a certain element. The isotopes are ionized so that they carry the same charge Q, and enter a speed selector as shown. Only those isotopes with a definite speed can pass straight through the mutually perpendicular uniform electric and magnetic fields in the speed selector. The whole set-up is in a vacuum environment.

When entering the magnetic field, all ions describe circular arcs and strike the photographic plate P. For particles of mass M, the radius r of the path is given by

Q v B1 = , r = .

If B1 is constant, r is directly proportional to M (assuming Q is the same for all ions). When ions with different masses are present each set produces a definite line and from their positions the (relative) masses can be found.Question : What is the objective of this experiment? (1 mark)

AnswerObjective : Determination of the relative mass of the isotopes. 1A


Assessing areaB. Apparatus : The list of apparatus and materials used.

Exercise : B_1The diagram shows a set-up used to measure the speed of a bullet in the laboratory.

The bullet (of mass m, in the form of a small metal ball) is ‘fired’ horizontally towards a block of wood (of mass M, in which a hole has been drilled) suspended from two vertical inextensible strings (each of length L). On striking the block, the bullet is embedded and the block rises by swinging through an angle θ as shown.Question : List out all the apparatus of this experiment. (2 marks)

AnswerApparatus : 1 bullet, 1 block of wood, 2 inextensible strings. Half correct 1A, all correct 2A.

Exercise : B_2Use a thermocouple - small thermal capacity, and can react rapidly (establishing thermal equilibrium) so as to follow varying temperatures.

Question : List out all the apparatus of this experiment. (2 marks)

AnswerApparatus : 2 cells, 1 beaker with ice, 1 beaker with water, 2 resistors, 2 cupper wires, 1 Pt-Rh

wire, 1 Pt wire. Half correct 1A, all correct 2A.


Exercise : B_3The following set-up is an experiment for measuring the rate of diffusion of bromine into air and hence estimating the mean free path of bromine molecules.


AnswerApparatus : Bromine liquid, 1 glass tube, 1 bromine capsule, 1rubber tubing, 1 V-shaped tube.

Half correct 1A, all correct 2A.

Exercise : B_4For measuring the surface tension of water using the rise of water in a glass capillary tube, we first set up the apparatus as shown below.


AnswerApparatus : 1 travelling microscope, 1 capillary tube, 1 pin, 1 beaker with liquid.


Exercise : B_5An experiment showing the phase change of the particle oscillations with distance from a sound wave source.



AnswerApparatus : 1 a.f. oscillator, 1 loudspeaker, 1 optical bench, 1 microphone, 1 double beam

oscilloscope. Half correct 1A, all correct 2A.

Exercise : B_6A prism spectrometer experiment.

C - collimator, T – TelescopeQuestion : List out all the apparatus of this experiment. (2 marks)

AnswerApparatus : 1 collimator, 1 telescope, 1 prism. Half correct 1A, all correct 2A.

Exercise : B_7The set-up shown below is used to investigate the potential around a charged sphere.



AnswerApparatus : 1 e.h.t. power supply, 1 nylon fishing line, 1 plastic football coated with aquedag, 1

flame probe, 1 gold-leaf electroscope with lamp behind, 1 protractor.Half correct 1A, all correct 2A.

Exercise : B_8The following diagram shows an arrangement for investigating the factors which determine the charge stored in a parallel-plate capacitor.


AnswerApparatus : 1 d.c. supply, 1 potential divider, 1 voltmeter, 1 microammeter, 1 reed switch coil, 1

parallel plates. Half correct 1A, all correct 2A.


Exercise : B_9The circuit of a d.c. power pack used for generating a variable d.c. voltage from the a.c. mains is shown below.


AnswerApparatus : 1 a.c. supply (240 V 50 Hz), 1 transformer, 4 diodes, 2 capacitors (32 F), 1 inductor

(20 H), 1 potential divider. Half correct 1A, all correct 2A.

Exercise : B_10Set-up :


AnswerApparatus : 1 battery, 1 potential divider, 2 voltmeters, 2 resistors (10 kΩ and 2 kΩ), 1 transistor,

1 d.c. supply (5.0 V). Half correct 1A, all correct 2A.

Exercise : B_11Experiment for observing the absorption spectrum of iodine using a diffraction grating.


Vaporize some iodine crystals in a test tube by warming. View a straight filament lamp through iodine vapour with a diffraction grating, the grating should be set with its lines parallel to the filament of the lamp.Question : List out all the apparatus of this experiment. (2 marks)

AnswerApparatus : 1 straight filament lamp, 1 test tube with iodine vapour, 1 diffraction grating.


Exercise : B_12As shown below, in a gravitational analogue simulation of α-particle scattering by a thin metal sheet, balls are allowed to roll down a ramp chute on to a model ‘hill’ where they experience deflection.


AnswerApparatus : 1 ramp chute, 1 ball, 1 model ‘hill’ (3-dimensional). Half correct 1A, all correct 2A.


Assessing areaC. Setup : Diagram showing the setup with labels.

Exercise : C_1A long spiral spring of force constant k hangs vertically from a fixed support with a weight of mass m attached to its bottom end. If the weight is pulled downwards and then released show that the subsequent motion is s.h.m., with the displacement from the equilibrium position at any time t given by x = a cosω0t, where a is a constant and ω0 the natural angular frequency of oscillation.

Question : Draw a labeled set-up diagram in the spaces provided below. (2 marks)

AnswerDiagram 1A, labels 1A.

Exercise : C_2A light spring of force constant k is connected to a block of mass m on a frictionless surface inclined at an angle θ to the horizontal. The block is displaced from its equilibrium position O and then released. Suppose at a certain instant the displacement of the block from the equilibrium position is x as shown.




Exercise : C_3A spring is held vertically with a weight, attached to its lower end. It is made to oscillate vertically by a periodic up-and-down motion of the hand. On increasing the frequency of motion of the hand, it is observed that the amplitude of motion of the weight increases, becoming a maximum at a certain frequency.



Exercise : C_4In an experiment, we use a moving-coil meter. The moving-coil meter has many parts : pointer, coil, permanent horseshoe magnet, concave pole piece, pivot, hair spring, jeweled bearing, fixed soft iron cylinder.

Question : Draw a labeled set-up diagram of the moving-coil meter in the spaces provided below.(2 marks)



Exercise : C_5In an experiment, we use a simple d.c. motor using permanent magnets, coil, brushes and commutator.

Question : Draw a labeled set-up diagram of the d.c. motor in the spaces provided below. (2 marks)


Exercise : C_6As part of a musical instrument, a uniform wire is held taut but unstretched between a fixed point and a smooth cylindrical peg of radius 1 cm. The tension in the wire can be increased by rotating


the peg about its fixed axis so that some wire is wound onto the peg. Two knife edges, A and B, are placed 0.36 m apart under the wire and push the wire stretched upward. The final shape of the wire is like a bridge.Question : Draw a labeled set-up diagram in the spaces provided below. (2 marks)


Exercise : C_7

The viscosity of a liquid can be measured by using Stokes’ law. Ball-bearings are dropped into a long vertical glass tube containing the liquid and their respective terminal velocities are measured for calculating the coefficient of viscosity of the liquid. Two markers A and B are stickled on the top and the bottom of the glass tube respectively.




Exercise : C_8A cart is accelerated from rest across a horizontal table. The cart is connected with a mass A by a string through a pulley at the corner of the table. The cart has a vertical post at one side, on which a ball is held by an electromagnet at a height of 0.50 m above the cart. When the mass A is released, it falls vertically and pulls the cart to move horizontally on the table.




Assessing areaD. Theory (optional) : Using physics’ theory to explain the experiment and derive the equation.

Exercise : D_1In a laboratory a small weight is attached by a piece of string of length l to a fixed point and set into circular motion in a horizontal plane. The set-up is shown below.

Question : Derive an expression for the angle of inclination of the string with the vertical q in terms of g, l and ω. (4 marks)

AnswerT is tension in string, F centripetal force.Resolving (1) vertically, mg = T cosq, Forces (2) horizontally F = T sin q. 1A+1A

As F = ml sinq w2 , hence, cosq = . 1A+1A

Exercise : D_2To study a circular motion, a small rubber bung of mass m is attached to one end of a piece of string passing through a thin glass tube, which has a weight W hanging at its other end. The rubber bung is set into a horizontal circular motion by a student holding the glass tube.


Question : Show that the weight W equals mω2L in theory, where ω is the angular speed and L is the length of the string beyond the upper opening of the glass tube. (3 marks)

AnswerThe string dips so that the vertical component of the tension balances the weight of the rubber bung.

W cosθ = mω2 r (as T = W) 1A W cosθ = mω2 (L cosθ) 1A

W = mω2 L 1A

Exercise : D_3

The diagram shows a set-up used to measure the speed of a bullet in the laboratory.

The bullet (of mass m, in the form of a small metal ball) is ‘fired’ horizontally towards a block of wood (of mass M, in which a hole has been drilled) suspended from two vertical inextensible strings (each of length L). On striking the block, the bullet is embedded and the block rises by swinging through an angle θ as shown.Question : By applying conservation laws, show that the speed of the bullet is given by the

relation where g is the acceleration due to gravity.

(4 marks)

Answer1. The horizontal momentum of the system is conserved, therefore mv = (m + M)V where V is the

common velocity just after impact. 1A


2. After the collision, the only forces acting on the system (block + bullet) are the weight and the string tensions (which do no work), therefore the mechanical energy is conserved. 1A

3. From energy conservation, (m + M)V2 = (m + M)gh . 1A

As h = L(1 – cosθ), by eliminating V, we hav . 1A

Exercise : D_4

For an experiment of a vertical mass-spring oscillating system, we know that T = . In order

to plot a linear graph, we plot T x against m. Find the value of x and the meaning of the slope of this graph. (2 marks)

Answer

x = 2 and slope = . 1A+1A

Exercise : D_5

For an experiment of a simple pendulum, we know that T = . In order to plot a linear graph,

we plot T y against l. Find the value of y and the meaning of the slope of this graph. (2 marks)

Answer

y = 2 and slope = . 1A+1A

Exercise : D_6A block of mass m moves freely on a horizontal ground with a dynamic coefficient of friction μ. If the initial speed of the block is u, derive a expression for the stopping distance of the block in terms of u, μ and g, where g is the gravitational acceleration constant. (4 marks)

AnswerAs friction f = –μN = –μmg 1A


So F = ma, –μmg = ma, a = –μg. 1AAlso v2 = u2 + 2as

0 = u2 + 2(–μg)s 1A

s = 1A

Exercise : D_7Figure below shows an experiment of a man of mass m standing against the wall of a cylindrical compartment called a ‘rotor’. The level of the rotor’s floor can be adjusted. The diameter of the rotor is d.

The rotor is spun at a certain speed about its central vertical axis so that, at this angular speed, the man remains ‘pinned’ against the wall even if the floor of the rotor is pulled downwards. FA is the friction and FB is the normal reaction by the wall. It is known that the maximum value of FA equals μFB. Derive an expression of the minimum angular speed ω, of the rotor needed to keep the ‘pinned’ against the wall in terms of d,μ and the gravitational acceleration constant g. (4 marks)

AnswerFA = mg 1A

max FA =μFB 1Amg ≦μmω2r 1A

ω2 ≧

ω ≧ 1A

Exercise : D_8

In an experiment, two identical pans, each of mass m, are connected by a light string which passes


over a light pulley suspended from the ceiling. The pulley can rotate smoothly about a horizontal axis through its centre. Two different weights m1 and m2 (m2 > m1) are placed on the pans as shown below.

Neglecting the air resistance, derive an expression for the vertical acceleration a of the weight m1 in terms of g, m, m1 and m2. (3 marks)

AnswerNet downward force = (m + m2) g – (m + m1) g = (m2 – m1) g. 1M+1A

Downward acceleration a = . 1A


Assessing areaE. Procedures : The procedures showing a logical ordering of steps. You may write them in points

form.

Exercise : E_1Experiment investigating the dependence of the stopping distance of a vehicle on its initial kinetic energy under the action of a constant resistive force.

Set up the tilting runway as shown. Arrange a light gate for measuring the speed of the trolley near the lower end of the tilting runway. The speed of the trolley is calculated from the time taken for the card to pass the light gate. Measure the stopping distance of the trolley, which is from the light gate up to the place where it stops. Repeat the experiment by releasing the trolley at different heights. Plot a graph of stopping distance against the square of the speed recorded (representing the kinetic energy of the trolley). A linear graph should be obtained showing the stopping distance is directly proportional to the kinetic energy.

Question : Write down the procedures of this experiment. (2 marks)

Answer1. Set up the tilting runway as shown. Arrange a light gate for measuring the speed of the trolley

near the lower end of the tilting runway.2. Measure the time taken for the card to pass the light gate and hence calculate the speed of the

trolley.3. Measure the stopping distance of the trolley, which is from the light gate up to the place where

it stops.4. Repeat steps 1 to 3 for releasing the trolley at different heights. 5. Plot a graph of stopping distance against the square of the speed recorded (representing the

kinetic energy of the trolley). A linear graph should be obtained showing the stopping distance is directly proportional to the kinetic energy.


Exercise : E_2An experiment measuring the moment of the inertia of a flywheel.

A mass M is attached to the end of string which has its other end threaded through a hole in the axle A of the flywheel W, the string being wound around the axle. When the mass M dropped the string is unwound and when M reaches the ground the string just slips off axle, allowing it to continue to turn. Let no. of revs. of W until M hits ground be n and the further no. of revs. after this until W comes to rest be n’ - and time t is taken by a stopwatch. The no. of revs. can be obtained by observing a mark on rim of flywheel, R.


Answer1. Set up the apparatus as shown.2. Attach a mass M to the end of string which has its other end threaded through a hole in the axle

A of the flywheel W, the string being wound around the axle. 1A3. Release the mass M and the string is unwound. 1A4. When M reaches the ground the string just slips off axle, allowing it to continue to turn. 1A5. Measure n, no. of revs. of W until M hits ground and n’, the further no. of revs. after this until

W comes to rest by observing a mark on rim of flywheel, R 1A6. At the same time, measure time t by a stopwatch. 1A

Exercise : E_3


Two identical loudspeakers connected to the same signal generator are placed inside a room as shown. All the surfaces of the room are covered with sound-absorbing materials. Point O is equidistant from the loudspeakers and line XOY is parallel to the line joining the loudspeakers. The variation of sound intensity along XOY is shown below :


Answer1. Set up the apparatus as shown.2. Connect the two identical loudspeakers to the same signal generator. 1A3. Cover all the surfaces of the room with sound-absorbing materials. 1A4. Measure the variation of sound intensity along XOY. 1A

Exercise : E_4Finding the speed of sound in air by using Kundt’s tube together with a loudspeaker.

The loudspeaker produces progressive longitudinal waves travelling towards the end of the cylinder


where they are reflected to interfere/superpose the incident waves. The frequency of the sound/signal generator is varied until resonance occurs. The stationary wave formed is revealed by the lycopodium powder which swirls away from the antinodes (where the air is vibrating strongly) and heaps are formed at the nodes. By measuring the average separation between the heaps (or nodes), d. The speed of sound in air equals f (2d) where f = frequency of the sound waves.


Answer1. Set up the apparatus as shown.2. Vary the frequency of the sound/signal generator until resonance occurs. 1A3. Observe the stationary wave formed from the lycopodium powder which swirls away from the

antinodes (where the air is vibrating strongly) and heaps are formed at the nodes. 1A4. Measure the average separation between the heaps (or nodes), d. 1A5. Calculate the speed of sound in air which equals f(2d) where f = frequency of the sound waves.

1AExercise : E_5An experiment demonstrating the wave nature of light and estimating the wavelength of the light.

The filament lamp acts as a single slit, and the diffracted light beams from the two narrow slits overlap in the region beyond the slits (accept idea presented using diagram). Use a filter to obtain monochromatic light so that alternate bright and dark, equally spaced interference fringes are observed (at the cross-wires of the travelling eyepiece). This shows the wave nature of light. The average fringe spacing y is found by measuring across as many fringes as possible with the travelling eyepiece. A metre rule is used to measure the separation d between the double slit and the


travelling eyepiece. The slit separation a is measured directly with a travelling microscope. The

wavelength λ of the monochromatic light is approximated by λ = .


Answer1. Set up the apparatus as shown.2. Use a filter to obtain monochromatic light and observe alternate bright and dark, equally

spaced interference fringes at the cross-wires of the travelling eyepiece. This shows the wave nature of light. 1A

3. Measure across as many fringes as possible with the travelling eyepiece, find the average fringe spacing y. 1A

4. Use a metre rule to measure the separation d between the double slit and the travelling eyepiece. Measure the slit separation a directly with a travelling microscope. 1A

5. Calculate the wavelength λ of the monochromatic light approximatly by λ = . 1A

Exercise : E_6An experiment measuring the wavelength of monochromatic light using a spectrometer and a diffraction grating

Usual adjustments are first made on (i) cross-wires, (ii) telescope and (iii) collimator of the spectrometer so that the collimator produces parallel light and the telescope focuses it at the cross-wires. The table with the grating are turned so that the incident light falls on the grating normally. The telescope is rotated, say to T1, and the reading corresponding to the first-order image is taken. The first-order reading on the other side of the normal, say at T2, is also taken.


Halve the angle between these two readings gives θ, from which λ can be calculated using nλ = d sinθ where d is the grating spacing and n = 1.


Answer1. Set up the apparatus as shown.2. Make usual adjustments on (i) cross-wires, (ii) telescope and (iii) collimator of the

spectrometer so that the collimator produces parallel light and the telescope focuses it at the cross-wires. 1A

3. Turn the table with the grating so that the incident light falls on the grating normally. 1A4. Rotate the telescope, say to T1, and take the reading corresponding to the first-order image. 1A5. Also take the first-order reading on the other side of the normal, say at T2, 1A6. Halve the angle between these two readings gives θ, hence calculate λ by nλ = d sinθwhere d

is the grating spacing and n = 1. 1A

Exercise : E_7An experiment investigating the variation of magnetic flux density along the axis of a solenoid by using a Hall probe.


Place the solenoid along east-west direction so that it is perpendicular to the earth’s magnetic field. (or, before making any measurement, adjust the potentiometer in the control box to set the millivoltmeter to zero.) The current should be kept constant. Slightly move the semiconductor slice inside the solenoid and record the maximum Hall voltage to ensure that the slice is perpendicular to the magnetic field in the solenoid. Repeat the procedure at different positions along the solenoid, so as to obtain the variation of magnetic flux density along the axis of the solenoid.


Answer1. Set up the apparatus as shown.2. Place the solenoid along east-west direction so that it is perpendicular to the earth’s magnetic

field. (or, before making any measurement, adjust the potentiometer in the control box to set the millivoltmeter to zero.) 1A

3. Keep the current constant. 1A4. Slightly move the semiconductor slice inside the solenoid and record the maximum Hall

voltage to ensure that the slice is perpendicular to the magnetic field in the solenoid. 1A5. Repeat step 4 at different positions along the solenoid, so as to obtain the variation of magnetic

flux density along the axis of the solenoid. 1A

Exercise : E_8Using a simple current balance, an experiment investigates how the magnetic force depends on the length of the current-carrying conductor in the magnetic field.


Set up the current balance and place one pair of magnadur magnets around the current-carrying arm.With one rider placed on the arm, adjust the current by shifting the rheostat to restore the balance.With the current remains unchanged, place another pair of magnadur magnets next to the first one.Equilibrium can be restored by placing another rider on the arm.This shows that the magnetic force (i.e. no. of riders) is directly proportional to the length of current-carrying conductor in the magnetic field.


Answer1. Set up the apparatus as shown.2. With one rider placed on the arm, adjust the current by shifting the rheostat to restore the

balance. 1A3. With the current remains unchanged, place another pair of magnadur magnets next to the first

one. 1A4. Place another rider on the arm to restore equilibrium. 1A5. This shows that the magnetic force (i.e. no. of riders) is directly proportional to the length of

current-carrying conductor in the magnetic field. 1A


Assessing areaF. Precautions : The precautions with relevant explanations.

Exercise : F_1The viscosity of a liquid can be measured by using Stokes’ law. Ball-bearings are dropped into a long vertical glass tube containing the liquid and their respective terminal velocities are measured for calculating the coefficient of viscosity of the liquid.

Question : What are the precautions of this experiment ? (3 marks)

AnswerAny THREE of the bellows @ 1A.1. The diameter of the tube is large compared with the diameters of ball-bearings so that

streamline conditions are satisfied.2. Marker A is far enough below the liquid surface for the ball-bearing to have its terminal

velocity at A.3. Dip the ball-bearing in the liquid and thereby coated, before dropping so as to reduce the

chance of air bubbles adhering to the falling ball-bearing.4. Avoid using ball-bearings of large radii as their terminal velocities are high and vortices may

form.5. Release the ball-bearing at the centre of the tube to reduce the effect of the wall of the tube on

the streamlines.6. Marker B is at a considerable distance from the bottom of the tube so as to reduce the effect of

the bottom of the tube on the streamlines.

Exercise : F_2Young’s double slit experiment shows that light propagates as a wave motion.



AnswerAny THREE of the bellows @ 1A.1. Light source should be strong (or black out the laboratory as much as possible) and properly

shielded so that no stray light falls on the screen.2. A monochromatic light source can be used in order to obtain sharper fringes.3. Both slits S1 and S2 should be as narrow as possible so that the light emerging from the slits

undergoes significant diffraction.4. The slits should be separated by a very small distance (~ 0.5 mm) so that the light from the two

slits overlap somewhere in front of the screen.5. The screen should be placed at an appreciable distance (1 ~ 2 m) from the slits so that the

separation of fringes is observable while the intensity is not too low.6. Make sure that the filament is parallel to the slits S1 and S2. (or if a source slit is used it should

be parallel to the two slits S1 and S2.)

Exercise : F_3Using a simple current balance, an experiment investigates how the magnetic force depends on the length of the current-carrying conductor in the magnetic field.


ProceduresSet up the current balance and place one pair of magnadur magnets around the current-carrying arm.With one rider placed on the arm, adjust the current by shifting the rheostat to restore the balance.With the current remains unchanged, place another pair of magnadur magnets next to the first one.Equilibrium can be restored by placing another rider on the arm.This shows that the magnetic force (i.e. no. of riders) is directly proportional to the length of current-carrying conductor in the magnetic field.Question : What are the precautions of this experiment ? (3 marks)

AnswerAny THREE of the bellows @ 1A.1. To avoid overheating, the current should be switched off as soon as observations have been

made and measurements taken.2. Make sure the direction of the magnetic field is perpendicular to the current-carrying arm.3. Shield the set-up from the disturbance of wind.4. Minimize the effect of the earth’s magnetic field by aligning the current-carrying arm along the

N-S direction.5 The set-up should be far from any current-carrying conductors so as to avoid the effect of stray

magnetic fields.

Exercise : F_4Experiment comparing viscosities of two liquids.


Ball bearings of radius a dropped in liquids and passage timed between marks A and B, where they should have reached a constant terminal velocity v0, using a stop-watch.Question : What are the precautions of this experiment ? (3 marks)

AnswerAny THREE of the bellows @ 1A.1. Ensure terminal velocity reached (vary position of A).2. Drop ball bearings vertically and along axis of cylindrical container.3. Use wide container or make correction for walls (could be estimated using different sizes).4. Timing accuracy could be increased by using laser beams/photo-diode ‘gates’ in positions A

and B and counting cycles of an a.c. oscillator ( f ~1 kHz).

5. Rub ball bearings in liquid before dropping in to prevent air bubbles from adhering onto the ball bearings.

Exercise : F_5

The above figure shows a simple pendulum experiment which consists of a bob suspended by a light, inextensible string of length L from a fixed point. If the bob is slightly displaced to one side and then released, it will perform s.h.m. The set-up can be used to measure the acceleration due to gravity g.


Measure the period T of the simple pendulum using a stop watch for different values of L. A graph of T2 against L is plotted which is a straight line passing through the origin.Question : What are the precautions of this experiment ? (2 marks)

AnswerAny TWO of the bellows @ 1A.1. Ensure the pendulum oscillates with small amplitude (less than 10∘).2. Make sure the pendulum oscillates on the same vertical plane.3. In measuring period T, at least 20 oscillations should be counted.

Exercise : F_6A student tries to measure the density of steel. He puts 20 identical steel ball bearings into a measuring cylinder half filled with water. Figure below shows the readings of the water level before and after placing the bearings into the cylinder. The ruler used is graduated in mm.


AnswerAny TWO of the bellows @ 1A.1. Avoid the formation of bubbles adhering the ball bearings, which will affect the volume

measured.2. Tilting the measuring cylinder and let the bearings run along the wall of the cylinder.3. Avoid the splashing of water when putting the bearings into the cylinder.

Exercise : F_7Your group decides to investigate the magnetic field pattern around two parallel current-carrying wires by using the following experiment. The set-up is shown below. With the time base of the CRO


switched off, a vertical trace is observed on the screen of the CRO. The measured result is very weak.


AnswerAny THREE of the bellows @ 1A.1. The length of the wire should be as long as possible ~ 2 m.2. The two wires should be well away from any magnetic materials.3. Set-up should be well away from any stray fields, such as those from mains socket.4. Twist the two connecting wires.5. Adjust the orientation of the coil so that the peak-to-peak value of the trace on the CRO is

maximum6. Avoid placing the coil near the ends of the wires

Exercise : F_8In this experiment, we study the equipotential lines and electric field lines by plotting equipotential lines on a high-resistance conducting surface.

Fix one fixed probe and one movable probe to the center-zero galvanometer. Hold the movable


firmly with your hand. Mark the position of the fixed probe on Move the movable probe on the conducting plate. The two probes are at the same potential when the galvanometer shows zero reading. Repeat it to obtain at least 7 points of the same potential. Draw a smooth line across these points. This line is an equipotential line.Question : What are the precautions of this experiment ? (2 marks)

AnswerAny TWO of the bellows @ 1A.1. The probe and the electrode never be too close together.2. The movable probe is hold firmly.3. Make sure the electrodes, probes and the plate are in conduction.


Assessing areaG. Results : All the original data and observation presented in appropriate forms such as tables.

Beware of the different units used for different apparatus, don’t mix them up. Keep the accuracy of the measured value consistent with the apparatus, i.e. you cannot use a metre rule to get a data 1.00047 m!

Exercise : G_1A student do an experiment. The followings are the raw data.L = 0.6 m, 50 T = 41, 43, 46 s. L = 0.8 m, 50 T = 51, 47, 48 s. L = 1.0 m, 50 T = 55, 53, 58 s.m =0.20 kg.Question : Fill in the table below with the raw data and make the necessary calculation. (2 marks)Length of string L / m

Time for 50 revolutions 50 T / sFirst trial

Second trialThird trial

Average time for 50 revolutions 50 T / s

/ rad s-1

mω2L / NAnswerCorrectly fill in the measured data 1A, correctly calculate the results 1A.Length of string L / m 0.60 0.80 1.00

Time for 50 revolutions 50 T / sFirst trial 41 51 55

Second trial 43 47 53Third trial 46 48 58

Average time for 50 revolutions 50 T / s 43 49 55

/ rad s-17.3 6.4 5.7

mω2L / N 6.4 6.6 6.5

Exercise : G_2A student do an experiment. The followings are the raw data.m = 0.2 kg, T1 = 30 s, T2 = 31 s. m = 0.3 kg, T1 = 37 s, T2 = 35 s. m = 0.4 kg, T1 = 39 s, T2 = 44 s.Question : Fill in the table below with the raw data and make the necessary calculation. (2 marks)

Load, m ( )T1 ( )T2 ( )mean T

T2


AnswerCorrectly fill in the measured data 1A, correctly calculate the results 1A.

Load, m (kg) 0.2 0.3 0.4T1 (s) 30 37 39T2 (s) 31 35 44

mean T 30.5 36 41.5T2 930 1296 1722

Exercise : G_3A student do an experiment. The followings are the raw data.For wire A : Maximum load = 30 kg, Breaking stress = 2 000 N/m2, Young modulus = 206 N/m2.For the longer wire B : Maximum load = 40 kg, Breaking stress = 1 900 N/m2, Young modulus = 124 N/m2.Question : Fill in the table below with the raw data and make the necessary calculation. (2 marks)

First wire Shorter wireMaximum load ( )Breaking stress ( )Young modulus( )


First wire Shorter wireMaximum load (kg) 30 40

Breaking stress (N/m2) 2 000 1 900Young modulus (N/m2) 206 124

Exercise : G_4A student do an experiment. The followings are the raw data.1 : 3.0 V, 200 Hz, 20.5 mA. 2 : 3.0 V, 300 Hz, 31.2 mA. 3 : 3.0 V, 400 Hz, 39.5 mA.4 : 4.5 V, 200 Hz, 29.8 mA. 5 : 4.5 V, 300 Hz, 47.2 mA. 6 : 4.5 V, 400 Hz, 60.2 mA.C (mF) = I / ( V f )Question : Fill in the table below with the raw data and make the necessary calculation. (2 marks)Trial 1 2 3 4 5 6Battery e.m.f. V0 ( )Frequency f ( )Average current I ( )Capacitance C ( )

Mean capacitance C ( )AnswerCorrectly fill in the measured data 1A, correctly calculate the results 1A.


Trial 1 2 3 4 5 6Battery e.m.f. V0 (V) 3.0 3.0 3.0 4.5 4.5 4.5Frequency f (Hz) 200 300 400 200 300 400Average current I (mA) 20.5 31.2 39.5 29.8 47.2 60.2Capacitance C (mF) 0.034 0.035 0.033 0.033 0.035 0.033

Mean capacitance C (mF) 0.034

Exercise : G_5An experiment is done. The followings are the raw data.(t, VC) = (0 s, 0 V), (10 s, 2.0 V), (20 s, 3.8 V), (30 s, 5.4 V), (40 s, 7.0 V), (50 s, 7.8 V),

(60 s, 8.4 V).Question : Fill in the table below with the raw data and make the necessary calculation. (2 marks)

t ( )VC ( )ln (VC)


t (s) 0 10 20 30 40 50 60VC (V) 0 2 3.8 5.4 7.0 7.8 8.4ln (VC) - 0.69 1.34 1.69 1.95 2.05 2.13

Exercise : G_6An experiment is done. The followings are the raw data.Start measure VC at t = 0 s and take it in a 10 s interval.VC = 0 V, 0.40 V, 0.79 V, 1.21 V, 1.55 V.Initial charging current, I0 = 0.025 A and Q (C) = I0 t.Question : Fill in the table below with the raw data and make the necessary calculation. (2 marks)

t ( )VC ( )Q ( )


t (s) 0 10 20 30 40VC (V) 0 0.40 0.79 1.21 1.55Q (C) 0 0.25 0.50 0.75 1.00

Exercise : G_7An experiment is done. The followings are the raw data.For the first two trials, t = 30 s, 31 s, n1 = 20, 19, n2 = 31, 30.


The mean t = 30 s, n1 = 19, n2 = 31.Question : Fill in the table below with the raw data and make the necessary calculation. (2 marks)

First trial Second trial Third trial MeanTime t / s

No. of revolutions n1

No. of revolutions n2


First trial Second trial Third trial MeanTime t / s 30 31 29 30

No. of revolutions n1 20 19 18 19No. of revolutions n2 31 30 29 31

Exercise : G_8An experiment is done. The followings are the raw data.For l = 30 cm, T1 = 40 s and T2 = 42 s. For l = 40 cm, T1 = 33 s, T2 = 34 s.For l = 50 cm, T1 = 32 s and T2 = 31 s. For l = 60 cm, T1 = 27 s, T2 = 28 s.Question : Fill in the table below with the raw data and make the necessary calculation. (2 marks)

Length, l ( )T1 ( )T2 ( )mean T

T2


Length, l (cm) 30 40 50 60T1 (s) 40 33 32 27T2 (s) 42 34 31 28

mean T 41 33.5 31.5 27.5T2 1700 1100 990 760


Assessing areaH. Measured data : Getting the correct result by calculation and interpret it.

Exercise : H_1For an experiment measuring the moment of inertia of the flywheel, we have the following results:

First trial Second trial Third trial MeanTime t / s 8.5 7.9 8.3

No. of revolutions n1 11 12 10No. of revolutions n2 22 21 23

Complete the table above and find the moment of inertia of the flywheel (unit = kg m2) by the

equation : , where m = 1.2 kg, r = 0.4 m, h = 0.8 m and g = 9.8 N/kg.

(3 marks)

AnswerFirst trial Second trial Third trial Mean

Time t / s 8.5 7.9 8.3 8.2No. of revolutions n1 11 12 10 11No. of revolutions n2 22 21 23 22

Table 1A

= 53 kg m2. 1A+1A

Exercise : H_2For an experiment measuring dynamic coefficient of friction μ , we have the following results:

First trial Second trial Third trial MeanInitial speed u / m s-1 0.51 0.49 0.50

Stopping distance s / m 0.317 0.320 0.319Complete the table above and find the dynamic coefficient of friction μ by the equation :

s = , where g = 9.8 N/kg. (3 marks)


Initial speed u / m s-1 0.51 0.49 0.50 0.50


Stopping distance s / m 0.317 0.320 0.319 0.319Table 1A

s = , 0.319 = 0.0128 /μ,μ = 0.040. 1A+1A

Exercise : H_3For an experiment measuring maximum coefficient of friction μ , we have the following results:

First trial Second trial Third trial MeanAngular velocityω/ rad s-1 4.45 4.43 4.44

Diameter d / m 1.99 1.98 2.02Complete the table above and find the dynamic coefficient of friction μ by the equation :

ω = , where g = 9.8 N/kg. (3 marks)


Angular velocityω/ rad s-1 4.45 4.43 4.44 4.44Diameter d / m 1.99 1.98 2.02 2.00

Table 1A

ω = , 4.44 = ,μ = 0.50. 1A+1A

Exercise : H_4For an experiment measuring the gravitational acceleration g , we have the following results:

First trial Second trial Third trial MeanMass m / kg 0.205 0.210 0.200Mass m1 / kg 0.105 0.100 0.105Mass m2 / kg 0.110 0.105 0.110

Acceleration a / m s-2 0.079 0.077 0.078Complete the table above and find the gravitational acceleration g by the equation :

a = . (3 marks)



Mass m / kg 0.205 0.210 0.200 0.205Mass m1 / kg 0.105 0.100 0.105 0.103Mass m2 / kg 0.110 0.105 0.110 0.108

Acceleration a / m s-2 0.079 0.077 0.078 0.078Table 1A

a = , 0.078 = 0.00805 g, g = 9.69 m s-2. 1A+1A

Exercise : H_5For an experiment measuring the gravitational acceleration g , we have the following results:

First trial Second trial Third trial MeanLength l / m 0.40 0.39 0.39

Angular velocityω/ rad s-1 5.5 5.3 5.6Angleθ/ ∘ 34 37 35

Complete the table above and find the gravitational acceleration g by the equation : cosq = .

(3 marks)


Length l / m 0.40 0.39 0.39 0.39 Angular velocityω/ rad s-1 5.5 5.3 5.6 5.5

Angleθ/ ∘ 34 37 35 35Table 1A

cosq = , g = lω2 cosq = 0.39 ×5.52 ×cos35∘= 9.7 m s-2. 1A+1A

Exercise : H_6For an experiment measuring the angular velocity ω , we have the following results:

First trial Second trial Third trial MeanMass m / kg 0.10 0.09 0.08

Weight W / N 2.2 2.3 2.1Length L / kg 0.61 0.59 0.60

Complete the table above and find the angular velocityω by the equation : W = mω2 L. (3 marks)



Mass m / kg 0.10 0.09 0.08 0.09Weight W / N 2.2 2.3 2.1 2.2Length L / kg 0.61 0.59 0.60 0.60

Table 1AW = mω2 L, 2.2 = 0.09 ×ω2 ×0.60, ω = 6.4 rad s-1. 1A+1A

Exercise : H_7For an experiment measuring the speed v of a bullet, we have the following results:

First trial Second trial Third trial MeanMass of the bullet m / kg 0.020 0.019 0.018Mass of the block M / kg 1.00 1.01 1.02

Length L / m 0.50 0.49 0.50Angleθ/ ∘ 25 26 24

Complete the table above and find speed v of the bullet by the equation :

, where g = 9.8 N/kg. (3 marks)


Mass of the bullet m / kg 0.020 0.019 0.018 0.019Mass of the block M / kg 1.00 1.01 1.02 1.01

Length L / m 0.50 0.49 0.50 0.50Angleθ/ ∘ 25 26 24 25

Table 1A

= 50 m s-1. 1A+1A

Exercise : H_8An experiment demonstrating the interference of a 3 cm microwave using one microwave transmitter.


Interference occurs between the two wave-trains diffracted from the two slots that act as two coherent sources. The receiver detects the maxima and minima of the interference pattern as it is moved around. Constructive and destructive interference occur whenever the path difference of the

microwaves from the slots is nλ and respectively.

Question : How do you interpret the measured result? (2 marks)

Answer1. Interference do occurs in microwaves. 1A2. Wavelength of the microwaves can be found from the positions of constructive and destructive

interference. 1A


Assessing areaI1. Discussion : Interpretation of the graphical result.

Exercise : I1_1

The above figure shows a simple pendulum experiment which consists of a bob suspended by a light, inextensible string of length L from a fixed point. If the bob is slightly displaced to one side and then released, it will perform s.h.m. The set-up can be used to measure the acceleration due to gravity g.Measure the period T of the simple pendulum using a stop watch for different values of L. A graph of T2 against L is plotted which is a straight line passing through the origin.

Question : How do you interpret the graphical result? (1 mark)

Answer

T2 is proportional to L which is consistent with the theoretical formula T2 = . 1A

Exercise : I1_2An experiment illustrating the particle nature of light.

Monochromatic light (f varied using spectrometer) incident on metal X. Emitted photo-electrons collected by C and current measured by electrometer E. Vs is the stopping potential just stopping the collection of emitted photo-electrons.


Question : How do you interpret the graphical result? (2 marks)

Answer1. Vs is zero until a threshold of frequency f0 is attained by the frequency of the monochromatic

light. 1A2. After that, Vs increases linearly with frequency f. 1A

Exercise : I1_3Franck-Hertz experiment

The voltage +V is varied between the cathode and anode of a vacuum tube containing Hg vapor.A small retarding potential exists between an intermediate grid to prevent electrons reaching anode.


Answer1. As V increases, the current show periodic peaks and troughs. 1A2. The separation of adjacent peaks is 4.9 V. 1A3. Besides, the peaks and troughs increase as V increases. 1A

Exercise : I1_4From an experiment, a typical X-ray spectrum is obtained.



Answer1. Intensity is zero until a threshold of wavelength λmin is attained. 1A2. After that, intensity increases, follows by a gently decreases. 1A3. Besides, groups of sharp peaks are also observed. 1A

Exercise : I1_5An experiment measuring a radioactive half-life. Diagrams below show the set-up and the result.

The half-life t½ is the time for the number of disintegrating nuclei to fall to half itsinitial value.


Answer1. The radioactivity curve shows the typical decay characteristic. 1A2. The half-life can be found graphically by finding the length of t½. 1A


Exercise : I1_6Franck-Hertz experiment investigating the effect of varying the electron energy.


Answer1. As V increases, the current show periodic peaks and troughs. 1A2. Besides, the peaks and troughs increase as V increases. 1A

Exercise : I1_7An experiment showing the energy spectrum of the β-particles emitted naturally by some nuclei.


Answer1. As energy increases, the number of β-particles emitted increases and falls after attaining a

peak value. 1A2. The number of β-particles emitted drops to zero when energy increases to Emax. 1A


Exercise : I1_8For an experiment, a V/I against 1/I graph is plotted as below.

If V = ε – Ir, find the values of ε and r from the graph. (3 marks)

Answer

From V = ε – Ir, . 1A

So ε = slope of the graph = = 6.0 V, 1A

r = the magnitude of the y-intercept = 3.0 Ω. 1A


Assessing areaI2. Discussion : Error estimation of the measured result.

Exercise : I2_1A micrometer screw gauge is used to measure the diameter of a piece of wire. The following readings were obtained :mean zero reading -0.05 0.02 mm, andmean apparent diameter +1.05 0.02 mm.Write down the diameter of the wire together with its error. (2 marks)

Answer1.10 0.04 mm. 1A+1A

Exercise : I2_2A vernier caliper is used to measure the diameter of a piece of wire. The following readings were obtained :mean zero reading -0.3 0.2 mm, andmean apparent diameter +11.3 0.2 mm.Write down the diameter of the wire together with its error. (2 marks)

Answer11.6 0.4 mm. 1A+1A

Exercise : I2_3To determine the area of cross-section of a metal wire, a student measures its diameter and obtains a value of 0.10 mm, subject to an error of 0.02 mm. Write down an expression of the result.

(3 marks)

Answer0.0079 0.0031 mm2 1M+1A+1A

Exercise : I2_4The period of oscillation, T, of a simple pendulum is related to its length, l, by the formula


. To find experimentally the acceleration of free fall by using a simple pendulum, a

student takes the following measurements :time for 10 oscillations : 10.1 0.2 s,length of the pendulum : 0.234 0.001 m.Write down an expression of the result. (3 marks)

Answer9.1 0.4 m s-2 1M+1A+1A

Exercise : I2_5In an experiment to determine the period of oscillation, T, of a simple pendulum, the time, t, for a number of complete oscillations is taken. It is found that the time for 20 complete oscillations is 19.7 0.2 s. Find an expression of the measured period T. (2 marks)

Answer0.99 0.01 s. 1A+1A

Exercise : I2_6The formula T2 = 4π2l/g is used to calculate the acceleration due to gravity g. If the maximum percentage error of l = 3 %, the maximum percentage error of T = 4 %. Find the maximum percentage error for g. (2 marks)

Answer11 % 1M+1A

Exercise : I2_7The diameter of the bore of a capillary tube can be determined by introducing a small quantity of mercury into the capillary. It is possible to measure the length of the mercury thread to within 3 % and the mass of the mercury used to within 7 %. Assuming negligible error in the density of


mercury, find the maximum percentage error in the calculated diameter of the capillary bore. (2 marks)

Answer5 % 1M+1A

Exercise : I2_8In an experiment to measure the density of steel, a steel sphere was used. The following measurements were obtained :Mass of the sphere = 540 mg 1 mgDiameter of the sphere = 0.51 cm 0.01 cmEstimate the percentage error in the calculated value of the density of steel. (2 marks)

Answer6 % 1M+1A


Assessing areaI3. Discussion : Error estimation of the graphical result.

Exercise : I3_1

For an experiment of a vertical mass-spring oscillating system, we know that T 2 = . The

measured results are :Load, m (kg) 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

T 2 (s2) 0.24 0.55 0.81 1.02 1.35 1.59 1.82 2.07 2.53 2.69By plotting T 2 against m, find the measured value of k. Also by measuring the maximum and minimum slope of the graph, find the maximum percentage error of k. (4 marks)

AnswerMeasured value of k = 15 N/m. 1A+1APlot the maximum and minimum slope graphs 1A, calculate the maximum percentage error 1A.

Exercise : I3_2

For an experiment of a simple pendulum, we know that T 2 = . The measured results are :

Length, l (m) 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0T 2 (s2) 0.85 1.56 2.28 3.35 4.01 4.88 5.57 6.25 7.34 8.12

By plotting T 2 against l, find the measured value of g. Also by measuring the maximum and minimum slope of the graph, find the maximum percentage error of g. (4 marks)

AnswerMeasured value of g = 9.8 N/kg. 1A+1APlot the maximum and minimum slope graphs 1A, calculate the maximum percentage error 1A.

Exercise : I3_3For an experiment finding the stress-strain graph of copper wire. The cross-sectional area and the natural length of the copper wire are 0.126 mm2 and 2 m respectively. The results are shown below :

Load (N) 5 10 15 20 25 30 35 40 45 50Extension(mm) 0.61 1.27 1.94 2.58 3.17 3.87 4.44 5.12 5.77 6.39Stress (107 N/m2)Strain (10-3)

Complete this table. As Young modulus = stress / strain. By plotting stress against strain, find the


measured value of the Young modulus. Also by measuring the maximum and minimum slope of the graph, find the maximum percentage error of the Young modulus. (5 marks)

AnswerStress (107 N/m2) 3.99 7.94 11.90 15.87 19.84 23.81 27.78 31.75 35.71 39.68Strain (10-3) 0.31 0.64 0.97 1.29 1.59 1.94 2.22 2.56 2.89 3.20

Table 1AThe measured Young modulus is 1.24 ×1011 N/m2. 1A+1APlot the maximum and minimum slope graphs 1A, calculate the maximum percentage error 1A.

Exercise : I3_4For an experiment charging a capacitor at a constant rate. The results are shown below:

VC (V) 0 0.40 0.79 1.21 1.55Q (C) 0 0.25 0.50 0.75 1.00

Plot a Q against VC curve. Find the slope of the graph and the maximum error of it. (3 marks)

AnswerSlope = 0.65 C/V. 1APlot the maximum and minimum slope graphs 1A, calculate the maximum percentage error 1A.

Exercise : I3_5For an experiment discharging a capacitor by a resistor. The followings are the results:

t (s) 0 10 20 30 40 50 60 70Q (C) 5.05 3.45 2.55 1.85 1.35 0.92 0.69 0.47ln Q

Complete the table above and plot a ln Q against t curve. Find the slope of the graph and the maximum error of it. (4 marks)

Answert (s) 0 10 20 30 40 50 60 70

Q (C) 5.05 3.45 2.55 1.85 1.35 0.92 0.69 0.47ln Q 1.62 1.24 0.94 0.62 0.30 -0.08 -0.37 0.76

Table 1ASlope = -0.033 1A


Plot the maximum and minimum slope graphs 1A, calculate the maximum percentage error 1A.

Exercise : I3_6For an experiment discharging a capacitor via a resistor. The followings are the results:

t (s) 0 5 10 15 20 25 30 35Q (C) 5.05 3.45 2.55 1.85 1.35 0.92 0.69 0.47

Plot a Q against t graph and find the half-life of the graph. (2 marks)

AnswerThe half-life of the graph is about 10.4 s. 1A+1A

Exercise : I3_7In an experiment with an illuminated photocell using caesium as the cathode, a small current is detected by the microammeter even when the anode is made slightly negative with respect to the cathode, using the circuit as shown below.

The current falls to zero only when the reverse p.d. across the tube reaches a value Vs, which varies with the frequency f of the radiation used to illuminate the cathode. The following table shows the variation of Vs with f.

Vs (V) 0 0.25 0.50 0.75 1.00 1.25 1.50f (1014 Hz) 4.6 5.2 6.0 6.3 7.5 7.8 8.4

Plot a Vs against f curve. Find the slope of the graph and the maximum error of it. (3 marks)

AnswerSlope = 3.9 ×10-15 V s. 1APlot the maximum and minimum slope graphs 1A, calculate the maximum percentage error 1A.

Exercise : I3_8In an experiment to investigate the absorption of β and γ rays by materials, a source emitting β and γ rays is placed at a distance of about 5 cm from a G-M tube as shown in Figure below.


The count rates, N’, corrected for background, corresponding to different thicknesses, d, of lead absorber plates are tabulated as follows :

d / mm 1 2 3 4 5 6 7N’ / s-1 29.0 24.8 22.0 20.0 18.2 16.8 16.0ln N’

Complete the table on the previous page and plot a graph of ln N’ against d. Also find the slope of the graph and the maximum error of it. (4 marks)

Answerd / mm 1 2 3 4 5 6 7N’ / s-1 29.0 24.8 22.0 20.0 18.2 16.8 16.0ln N’ 3.37 3.21 3.09 3.00 2.90 2.82 2.77

Table 1A

Slope = = - 0.1 mm-1. 1A


Exercise : I3_9In an experiment, a student wants to determine the gravitational acceleration g at the earth’s surface. He releases a block from rest and uses a stroboscope to take a photograph of the block’s downward motion. The result is as shown. The time interval between successive exposure is 0.1 s and the first exposure is at t = 0s when the disc is released.

time t / s 0 0.1 0.2 0.3 0.4 0.5 0.6position s / m 0 0.03 0.22 0.45 0.79 1.29 1.79

time t2 / s2

Complete the above table and plot a graph of s against t2. By the equation , find measured

value of g and the maximum error of it from the graph. (5 marks)

Answertime t / s 0 0.1 0.2 0.3 0.4 0.5 0.6


position s / m 0 0.03 0.22 0.45 0.79 1.29 1.79time t2 / s2 0 0.01 0.04 0.09 0.16 0.25 0.36

Table 1A

Slope of the graph = 1.80 / 0.36 = 5 m s-2 = , hence the measured value of g = 10 m s-2. 1A+1A


Exercise : I3_10In order to detect the acceleration of a car, a driver starts the car from rest with constant acceleration. Another man on the ground use a laser detector to detect the speed of the car. The result is as shown. The first detection is at t = 0 s when the car starts its motion.

position s / m 0 0.14 0.62 1.35 2.36 3.79speed v / m s-1 0 1.5 3.0 4.5 6.0 7.5

speed v2

Complete the above table and plot a graph of s against v2. By the equation v2 = 2 a s, find measured value of a and the maximum error of it from the graph. (5 marks)

Answerposition s / m 0 0.14 0.62 1.35 2.36 3.79speed v / m s-1 0 1.5 3.0 4.5 6.0 7.5

speed v2 0 2.25 9.00 20.25 36.00 56.25Table 1A

As v2 = 2 a s, s = v2, so slope = . 1A

Slope of the graph = 3.76 / 56.3 = 0.0668 = , hence the measured value of a = 7.49 m s-2. 1A



Assessing areaI4. Source of errors : State the source of errors and limitations of the method used, suggestions for

improvement and further investigation. As you should try your best to eliminate the personnel error as stated in the precaution, personnel error, i.e. taking the data erratically, is not acceptable as a source of error.

Exercise : I4_1An experiment demonstrating the relation between the angular velocity of the bodyand the radius of the path.

The glass tube is held vertically, the bung is whirled around above his head by one student and the speed of bung is increased until the marker is just below tube. Another student times, say, 50 revolutions of the bung. By moving marker the length l of the string can be varied and the relation between l and the angular velocity (w) obtained.

Question : What are the sources of errors of this experiment? (3 marks)

AnswerAny THREE of the bellows @ 1A.1. Friction exists at the opening of the glass tube.2. The rubber bung is not swirled with constant speed.3. The string is not inextensible.4. The rubber bung is not swirled in a horizontal circle.

Exercise : I4_2An experiment verifying a pendulum undergoes s.h.m.


Ticker tape is attached to weight. Weight released from position (1) and swings to position (2), ticker timer having been switched on. The dots on tape indicate displacements for equal time intervals of 0.02s/0.01s. Using tape a displacement/time graph is plotted. Velocity at different times is obtained by drawing a tangent at particular point on plot and determining slope.


AnswerAny THREE of the bellows @ 1A.1. Not S.H.M. : Due to finite amplitude the approximation sin q = q does not hold.2. Damping of motion by ticker tape may seriously affect the period.3. Not a point mass and so there is difficulty in measuring l.4. Buoyancy of the air will reduce downward force on mass - affecting Period.

Exercise : I4_3Objective : Investigating the geometric factors affecting the capacitance of a parallel plate capacitor.


Reed switch, switches alternately between contacts (1) and (2), charging C and then discharging C with a frequency f. The generated current pulses are so rapid that the micro-ammeter deflection remains steady, indicating an average current I, where I = Qf. Q being charge stored in C. Hence capacitance of capacitor C = Q / V , V being measured by a voltmeter. Clearly the area of overlap of plates A and the separation d (using various spacer thicknesses) can be varied and effects on C determined.


AnswerAny THREE of the bellows @ 1A.1. R should prevent excessive current pulses but not be too large otherwise C does not completely

discharge2. Finding effect of electric field at edges of plates affects dependence of C on areas A.3. Stray capacitances to earth could affect the effective capacitance of C.4. Leakage of charge from capacitor5. Rebound of contact in reed switch.

Exercise : I4_4To study a circular motion, a small rubber bung of mass m is attached to one end of a piece of string passing through a thin glass tube, which has a weight W hanging at its other end. The rubber bung is set into a horizontal circular motion by a student holding the glass tube.



AnswerAny THREE of the bellows @ 1A.1. The string is extensible.2. The rubber bung is not swirled in a horizontal circle.3. Friction exists at the opening of the glass tube.4. The rubber bung is not swirled with constant speed.

Exercise : I4_5Experiment investigating the dependence of the stopping distance of a vehicle on its initial kinetic energy under the action of a constant resistive force.

Set up the tilting runway as shown. Arrange a light gate for measuring the speed of the trolley near the lower end of the tilting runway. The speed of the trolley is calculated from the time taken for the card to pass the light gate. Measure the stopping distance of the trolley, which is from the light gate up to the place where it stops. Repeat the experiment by releasing the trolley at different heights. Plot a graph of stopping distance against the square of the speed recorded (representing the kinetic energy of the trolley). A linear graph should be obtained showing the stopping distance is directly proportional to the kinetic energy.

Question : What are the sources of errors of this experiment? (1 mark)

Answer


1. The friction at the wheels of the trolley is not constant. 1A

Exercise : I4_6A long spiral spring of force constant k hangs vertically from a fixed support with a weight of mass m attached to its bottom end. If the weight is pulled downwards and then released show that the subsequent motion is s.h.m., with the displacement from the equilibrium position at any time t given by x = a cosω0t, where a is a constant and ω0 the natural angular frequency of oscillation.


AnswerAny TWO of the bellows @ 1A.1. The mass oscillates with large amplitude such that the spring doesn’t obey Hooke’s law.2. The mass doesn’t oscillate vertically.3. In measuring period, only a few oscillations is counted.

Exercise : I4_7A student wants to use an ‘inertia table’ to determine the moment of inertia of a cylinder about its central axis. The inertia table consists of a circular platform suspended by a wire, and can be set into torsional oscillations. The cylinder is placed on the platform with its axis lying along the line AO.



AnswerAny THREE of the bellows @ 1A.1. Difficulty in locating axis of cylinder along OA.2. Cylinder may slip on the table during oscillation.3. Oscillation has too large amplitude.4. The motion is not purely torsional oscillation.

Exercise : I4_8A student use the apparatus shown below to determine the speed of sound in air. The distances between the loudspeaker L and the reflecting plate R are measured by a metre rule with different frequencies recorded from the screen of the signal generator.

Question : What are the sources of systematic errors of this experiment? (2 marks)

AnswerThere exists systematic error in the measurement of the positions of M by the metre rule and in the readings of the frequencies of the signal generator. 1A+1A


Assessing areaJ. Conclusion : State the conclusion supported by reasoned arguments. The final result together

with its error MUST be stated in the conclusion. Don’t just write one sentence for the conclusion, you should write a few sentences to explain the reasons supporting the conclusion.

Exercise : J_1A long solenoid carrying constant current will give a uniform magnetic field inside the solenoid. Set up the apparatus as shown.

Adjust the rheostat so that there is a current of about 1 A through the solenoid. Insert the Hall probe well inside the solenoid and adjust for zero deflection of the galvanometer before switching on the current. Switch on the current and set the galvanometer to give a (large) deflection. Move the probe about inside the solenoid over a cross-section and along the length of the solenoid.The deflection of the galvanometer remains unchanged, which indicates the magnetic field due to the solenoid is uniform.Question : What is the conclusion of this experiment? (1 mark)

AnswerConclusion : The magnetic field inside a solenoid is uniform. 1A

Exercise : J_2

A very penetrating radiation X (unaffected by magnetic fields and so not charged particles) was observed when beryllium was bombarded by -particles. This radiation was found to be capable of producing protons from paraffin-wax – a measure of their energy/velocity was obtained by inserting thin sheets of mica until no current registered by the ionisation chamber. Experiment was repeated with nitrogen in place of the paraffin-wax (hydrogen nuclei). Chadwick from a consideration of the


conservations of linear momentum/ energy to the proton collisions (assumed elastic) calculated the rest mass of a neutron ~ that of a proton.Question : What is the conclusion of this experiment? (1 mark)

AnswerConclusion : The rest mass of a neutron is approximately the same as that of a proton. 1A

Exercise : J_3

Connect a high resistance voltmeter (0 – 15 V) across the terminals of a low voltage power supply and adjust the output to 12 V, which is the e.m.f. E of the supply. The voltmeter reading drops slightly after connecting the ray-box lamp and the ammeter.Record the voltmeter reading V and the ammeter reading I. (I can also be estimated from the ratings of the lamp 12 V 24 W without using the ammeter) The internal resistance r of the supply is given

by r = where I is the current delivered.

Question : What is the conclusion of this experiment? (1 mark)

AnswerConclusion : The internal resistance of the supply is r. 1A

Exercise : J_4

Interference takes place between mono-chromatic X-rays reflected from atoms spaced throughout crystal and in some directions of reflection maxima are detected – enables the separation of atomic planes in a crystal to be determined, since 2d sin q = n.Question : What is the conclusion of this experiment? (1 mark)

AnswerConclusion : The separation of atomic planes in a crystal is d. 1A


Exercise : J_5Set up a friction-compensated runway. To investigate the relation between force and acceleration, a trolley is pulled by one, two and three identical elastic strings which are stretched by the same amount. The corresponding accelerations are recorded and a graph of the force (number of elastic strings) is plotted against the acceleration, which shows a straight line passing through the origin (linear relationship). To investigate the relation between mass and acceleration, use one elastic string to pull one, two and three trolleys. The corresponding accelerations are recorded and a

graph of is plotted against the acceleration, which shows a straight line passing through the

origin (linear relationship). Thus, acceleration . For a body of mass 1 kg and moves with

acceleration 1 m s-2, the force acting on it is 1 N.


AnswerConclusion : Force mass × acceleration. 1A

Exercise : J_6Experiment investigating the dependence of the stopping distance of a vehicle on its initial kinetic energy under the action of a constant resistive force.

Set up the tilting runway as shown. Arrange a light gate for measuring the speed of the trolley near the lower end of the tilting runway. The speed of the trolley is calculated from the time taken for the card to pass the light gate. Measure the stopping distance of the trolley, which is from the light gate up to the place where it stops. Repeat the experiment by releasing the trolley at different heights. Plot a graph of stopping distance against the square of the speed recorded (representing the kinetic energy of the trolley). A linear graph is obtained


AnswerConclusion : The stopping distance is directly proportional to the kinetic energy. 1A


Exercise : J_7Glass tube is lowered slowly into the beaker of water until the air inside the tube is heard to vibrate loudly (with the frequency of the tuning fork). Then a stationary wave motion of the air in the tube is produced form the superposition of the incident and reflected waves from the air/ water surface.Resonant frequency, f0 = v/4l, where l is the air column length and v velocity of sound. By measuring f0 and l, the velocity of sound in air is found.


AnswerConclusion : The velocity of sound in air is v. 1A

Exercise : J_8Experiment for observing the absorption spectrum of iodine using a diffraction grating.

A continuous spectrum consisting of some dark lines is observed. The light from the lamp is a continuous spectrum consisting of photons of a range of energies. When the light is incident on an iodine molecule, it can only absorb energy from a photon whose energy is just enough for exciting it to a higher energy state. When the excited molecule returns to ground state, it re-emits light of the same wavelength of the photon but equally in all directions. So the intensity of the radiation in the direction of the incident photon is reduced. However, photons of other wavelengths will pass straight through. Thus a dark line, whose wavelength is that of the absorbed photon, is seen on the background of a continuous spectrum.


AnswerConclusion : The absorption spectrum of iodine is a continuous spectrum consisting of some dark

lines is observed. 1A


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