Practical Physics

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HIGHER SECONDARY PRACTICAL PHYSICS

LIST OF EXPERIMENTS

SECTION A

No Name of Experiment Page No

1 Vernier Calipers..…………………………………………………… 2

2 Screw Gauge……………………………………………………….. 4

3 Moment Bar…………………………………………………………. 6

4 Common Balance ………………………………………………….. 7

5 Concurrent Forces………………………………………………….. 8

6 Concurrent Forces - Relative Density……………………………. 9

7 Simple Pendulum …………………………………………………... 10

8 Helical Spring I………………………………………………………. 11

9 Helical Spring II……………………………………………………… 13

10 Resonance Column I……………………………………………….. 14

11 Resonance Column II………………………………………………. 15

12 Sonometer I………………………………………………………….. 16

13 Sonometer II……………………………………………………….... 17

SECTION B

14 Ohm’s Law..……….………………………………………………… 18

15 Metrebridge I………………………………………………………... 20

16 Metrebridge II……………………………………………………….. 21

17 Potentiometer I ……………………………………………………... 23

18 Potentiometer II……………………………………………………… 23

19 Galvanometer – Resistance and Figure of Merit ……………….. 24

20 P-N Junction Diode……………….………………………………… 25

21 Mapping of Magnetic field I (North Pole Pointing South)……….. 27

22 Mapping of Magnetic field II (North Pole Pointing North)………. 28

23 Concave Mirror……………………………………………………… 29

24 Convex Lens………………………………………………………… 31

25 Convex Mirror…..………………………………………………….... 33

26 Refraction Through a Prism ……………………………………….. 34

27 Refractive Index of Glass ………………………………………….. 35

* Experiments 6, 21, 22 are not included in the syllabus

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SECTION A 1. VERNIER CALIPERS

Aim

1 To measure the diameter of a sphere and hence to calculate its volume 2 To measure the diameter of a cylinder and hence to calculate its volume 3 To measure the internal diameter and depth of a calorimeter and hence to determine its

internal volume Apparatus

Vernier calipers, sphere, cylinder, calorimeter etc Principle Least count (LC) = _Value of one main scale division_ No. of divisions on the vernier scale

Total Reading = MSR + (VSR x LC) MSR → Main Scale Reading VSR → Vernier Scale Reading

Volume of Sphere = 34

3rπ r → radius of the sphere

Volume of cylinder = 2r lπ r → radius of the cylinder

l → length of the cylinder

Volume of calorimeter = 2r hπ r → internal radius of the calorimeter

h → depth of the calorimeter

Procedure To find the least count (LC) The value of one main scale division and the number of divisions on the vernier are noted. The least count of the instrument is calculated. Volume of sphere and cylinder The given sphere is gently gripped between the jaws. If a main scale division is exactly coinciding with the zero of vernier scale that is taken as the MSR, otherwise the main scale division immediately before the zero of vernier scale is taken as MSR. The vernier division which exactly coincides with any one of the main scale division is also noted (VSR). Total reading is calculated. The experiment is repeated by keeping the jaws at different diametrically opposite positions of the sphere and the mean diameter is determined. The volume of the sphere is calculated. Similarly the length and diameter of the cylinder are determined by properly gripping it in between the jaws and its volume is calculated. Volume of calorimeter The inner jaws are inserted into the calorimeter and are pulled apart till they touch the inner wall of the calorimeter at diametrically opposite points. The MSR and VSR are noted and the internal diameter is calculated. The experiment is repeated and the mean value is determined. To find the depth of calorimeter, the right edge of main scale is placed on the upper edge of the calorimeter. The jaws are pulled apart till the tip of the metallic pointer touches the bottom of the calorimeter. The MSR and VSR are noted and the depth is calculated. The experiment is repeated and the mean value of depth is determined. Knowing diameter and depth the volume of the calorimeter is calculated.

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Observations and calculations Value of one main scale division = mm = cm Number of divisions of the vernier = Least count (LC) = _Value of one main scale division_ No. of divisions on the vernier scale = = cm To find the volume of the sphere

No MSR VSR Total Reading =

MSR + (VSR x LC) Mean

cm cm cm

Mean diameter of the sphere = m Radius of the sphere (r) = m

Volume of the sphere = 34

3rπ

= = m

3

To find the volume of the cylinder

Dimensions No MSR VSR Total Reading =

MSR + (VSR x LC) Mean

cm cm cm

Diameter

Length

Mean diameter of the cylinder = m Radius of the cylinder (r) = m

Mean length of the cylinder ( l ) = m

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Volume of the cylinder = 2r lπ

= = m

3

To find the volume of calorimeter

Dimensions No MSR VSR Total Reading =

MSR + (VSR x LC) Mean

cm cm cm

Diameter

Depth

Mean diameter of the calorimeter = m Radius of the calorimeter(r) = m Depth of the calorimeter (h) = m

Volume of the calorimeter = 2r hπ

= = m

3

Result Volume of the sphere = m³ Volume of the cylinder = m³ Volume of the Calorimeter = m³

2. THE SCREW GAUGE Aim

1 To measure the diameter of a wire of known length and hence to calculate its volume 2 To measure the diameter of a sphere and hence to calculate its volume. 3 To find the volume of a glass plate by measuring its thickness using screw gauge and surface area using graph paper Apparatus Screw Gauge, wire, sphere, glass plate, graph paper, metre scale etc Principle Pitch = Distance moved No. of rotations Least Count (L C) = Pitch . No. of divisions on the head scale Total Reading = Pitch Scale Reading + (Corrected Head Scale Reading x Least Count) = PSR + (Corrected HSR x LC) Corrected Head Scale Reading = Head Scale Reading + Zero Correction

Volume of the wire =2r lπ r → radius of the wire

l → length of the wire

Volume of Sphere = 34

3rπ r → radius of the sphere

Volume of the glass plate = Area x Thickness

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Procedure Determination of Least count A certain number of rotations (say 5) are given to the screw and the distance moved by it is noted on the pitch scale. Pitch is calculated. Pitch divided by the number of divisions on the head scale gives the least count. Estimation of Zero Correction The screw is gently rotated till the faces A and B come in contact. If zero of the head scale coincides with the reference line, there is no zero correction. If the zero is above the reference line, correction is positive and if it is below, correction is negative. Determination of the volume of the wire

The wire is gently gripped between the faces A and B. The pitch scale reading is noted (PSR). The division on the head scale which coincides with the reference line is noted (HSR). The zero correction is applied to the observed HSR to get the Corrected HSR. Total reading is calculated. The experiment is repeated and hence mean diameter is calculated. The length of the wire is measured using a metre scale and hence the volume of the wire is calculated. Determination of volume of the Sphere The sphere is gently gripped between the faces A and B. Taking PSR and HSR at different orientations the mean diameter and hence volume is calculated. Determination of volume of the Glass plate The glass plate is gently gripped between the faces A and B. Taking PSR and HSR at different positions, mean thickness is calculated. The glass plate is then placed on a graph sheet and its outline is traced. Counting the number of squares trapped in the outline, the surface area of the glass plate is calculated. Knowing the thickness and area, volume is calculated. Observations and calculations

Distance moved for 5 rotations = mm Pitch = Distance moved for 5 rotations 5 = = mm Least Count (L C) = Pitch . No. of divisions on the head scale = = mm Zero Coincidence = Zero correction = div To find the volume of the wire

No PSR HSR Corrected

HSR

Total Reading = PSR + (corrected HSR x

LC) Mean

mm mm mm

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Mean diameter of the wire = m Radius of the wire (r) = m

Length of the wire ( l ) = cm

= m

Volume of the wire = 2r lπ

= = m

3

To find the volume of the sphere

No PSR HSR Corrected

HSR

Total Reading = PSR + (corrected HSR x

LC) Mean

mm mm mm

Mean diameter of the sphere = m

Radius of the sphere (r) = m

Volume of the sphere = 34

3rπ

= = m

3

To find the volume of glass plate

No PSR HSR Corrected

HSR

Total Reading = PSR + (corrected HSR x

LC) Mean

mm mm mm

Thickness of the glass plate (t) = m Area of glass plate (A) = cm

2

= m2

Volume of the glass plate = A x t = = m

3

Result Volume of the wire = m

3

Volume of the sphere = m3

Volume of the glass plate = m3

3. MOMENT BAR Aim To determine the mass of the given body using the principle of moments Apparatus Metre scale, stand, slotted weights, given body, string etc Principle

From the figure, M x OP = W x OQ

M = W x OQ OP

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Procedure The metre scale is suspended through its centre of gravity. The unknown mass (M) is suspended from the point P. Slotted weights (W) are suspended from the other side of the scale so that the scale again remains horizontal. The distances PO and OQ are measured and the unknown mass is calculated. The experiment is repeated by changing the slotted weights and the mean value of the mass (M) is calculated Observations and Calculations Centre of gravity O = cm

No Known Mass

W Distance

OQ Distance

OP M = W x OQ

OP Mean M

g cm cm g g

Mean mass of the body M = kg

Result

Mass of the given body = kg

4. COMMON BALANCE Aim To determine the mass of given body by sensibility method. Apparatus Common balance, weight box, given body etc. Principle

Sensibility of the common balance S =

0 1

0.01

R R− Ro = zero resting point

R1 = resting point with 10mg on the right pan. Correct mass of the body W = Wo + S (R - Ro)

Wo = Mass placed on the right pan.

R = resting point when the body is placed on the left pan and sufficient mass on the right pan.

Procedure

The balance is gently released by turning the handle. The scale pans are kept empty. The nuts at the ends of the beam are adjusted so that the pointer moves almost equally to either side of the central division. The beam is arrested. The balance case is now closed and the beam is again released. Five successive turning points on the scale are noted (three on the left and two on the right). The average of the turning points on the left and the average of the turning points on the right are found. Then mean of these two averages gives the zero resting point (RO). Now 10mg is added to the right pan. The resting point R1 is determined as before. The sensibility of the balance is calculated

Now the given body is placed on the left pan and

sufficient mass (Wo) are added in the right pan so that the

pointer swings over the scale almost equally. The resting point (R) is determined. The correct mass of

the body is calculated.

Scale of the balance

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Observations and calculations

Load in Pans Turning Points Mean Turning Points

Left Right Left Right Left Right Resting Point

Nil

Nil R0 =

Nil

10 mg R1 =

g mg

Given Body Total W0

= g

R =

Sensibility S = 0.01 R0 – R1

= = g / div Mass of the Body W = Wo + S (R - Ro) = = g = kg Result

Sensibility of the balance = g / div Mass of the given body = kg

5. CONCURRENT FORCES Aim

To find the weight of a given body using Parallelogram law of forces. Apparatus The parallelogram law apparatus (Gravesands apparatus), strings, weight hanger with slotted weights, Pins, Paper, given body etc. Principle

Let P and Q are the magnitudes of two vectors acting at a point and θ be the angle between them, the resultant vector.

R=2 2 2P Q PQCosθ+ +

If OC is the diagonal of parallelogram with P and Q as sides R = OC x Scale Procedure

A thread of suitable length, carrying two weight hangers at its ends is passed over the pulleys. Another thread is tied to the first at the point O between the two pulleys, so as to have a common knot at O.The weights P,Q and the body W are attached to the ends of the thread. A sheet of paper is fixed on the board behind the thread. The position of the common knot, directions OX, OY and OZ of the thread are marked on the paper. The paper is taken out. Choosing a suitable scale, OA and OB are marked on the paper, to represent P and Q respectively. The parallelogram OACB is completed. The diagonal OC is drawn. The length OC is measured and is multiplied by the scale factor to get the weight W of the body. The angle θ between the forces P and Q are measured and the weight of the body is calculated Observations and Calculations

Scale 1 cm = g wt

Forces No

P Q OA OB

Diagonal OC

Wt. of the Body=

OC x scale

θ = ∟XOY

R= 2 2 2P Q PQCosθ+ +

gwt gwt cm cm cm gwt degree gwt

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Weight of the given body: By measuring diagonal = gwt = kgwt By measuring angle = gwt = kgwt Result Weight of the given body By measuring diagonal = kgwt By measuring angle = kgwt

6. CONCURRENT FORCES – Relative Density Aim

To determine the relative density of the material the given body Apparatus Parallelogram law apparatus, given body, beaker containing water etc Principle Relative density of solid = Wt. of the solid in air Loss of Wt. in water

= a

a w

W

W W− aW - Wt of body in air

wW - Wt of body in water

The weight of the body is calculated using parallelogram law Procedure

The weight of the given body in air (aW ) is determined using the parallelogram law apparatus.

Now the given body is immersed in water without touching the bottom or sides of the beaker. The

weight of the body is determined ( wW ). The relative density is calculated.

Observations and Calculations

Forces Body No

P Q OA OB

Diagonal OC

Wt. of the Body=

OC x scale

Mean Wt

gwt gwt cm cm cm gwt

In Air

aW =

In water

wW =

Relative density of solid = a

a w

W

W W−

=

= Result

Relative density of the solid =

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7. SIMPLE PENDULUM Aim 1 To determine the acceleration due to gravity at the place. 2 To find the length of the seconds pendulum 3 To find the period of simple pendulum whose length is 105 cm Apparatus

A metallic bob, a thread of length 140cm, stand, meter scale, stopwatch etc. Principle:

For small oscillations, the period of oscillation

2 l

Tg

π=

where l the length of the pendulum and g is the acceleration due to gravity.

From the above relation

2

2g 4

l

Tπ=

Procedure

Radius of the bob is measured. One end of the thread is attached to the hook of the bob and the other end is passed through the cork fixed on the clamp stand. The length of the

pendulum l is the length from the point of suspension to the

centre of the bob. The length of the pendulum is made 50 cm. Using stopwatch time for 20 oscillations (t) is found out. The period

of the pendulumt

T=20

. Period of the pendulum is measured

for lengths 60cm, 70 cm, 80cm, 90 cm, 100cm, and 110 cm. In

each trial 2

l

T is

found to be a constant. Mean

2

l

Tis

calculated and hence g is calculated.

A graph is plotted with l along X axis and T2 along Y-axis. From the graph

AB

BCgives

2

l

T. Hence g

is calculated from the graph. Length of seconds pendulum and period of the pendulum for 105 cm can be calculated from the graph. Observations and calculations

Radius of the bob r = cm

Time for 20 oscillations

No

Distance between the

point of suspension and the bottom of the

bob

( l r+ )

Length Of the

Pendulum

( l ) 1 2 Mean

(t)

Period

tT=

20

T

2

2

l

T

Mean

2

l

T

cm cm s s s s s2 cm / s

2 cm / s

2

Mean 2

l

T = cm / s

2

= m / s2

Acceleration due to gravity 2

24

lg

Tπ=

= = m / s

2

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From the graph AB= cm = m BC= s

2

Acceleration due to gravity g = 4π2 AB

BC = = m / s

2

Length of the seconds pendulum (OD) = cm = m

Period of the pendulum whose length is 105 cm = OE

= = s Result Acceleration due to gravity at the place (1) by calculation = m / s

2

(2) from graph = m / s2

Length of seconds pendulum = m Period of simple pendulum whose length is 105 cm = s

8. HELICAL SPRING I Aim 1 To determine the spring constant of the helical spring by load – extension method 2 To determine the unknown mass Apparatus Helical spring apparatus, slotted weights, a body of unknown mass etc. Principle According to Hooke's law, within the elastic limit of a spring Load = K, the spring constant Extension

If l is the extension produced by a mass m, then

mg

Kl

=

If 'l is the extension produced by an unknown mass 'm , then

'

'Kl

mg

=

Procedure The position of the pointer on the scale is noted with the weight hanger (dead mass m0) alone. Suitable masses are added to the weight hanger in steps and in each case the position of the pointer on the scale is noted. The masses are then removed in steps and the corresponding readings of the pointer are

again noted. Now the extension ( l ) for each mass (m) is

determined by taking the difference between the corresponding scale reading and the dead position of the pointer. In each case

mg

lis determined. The mean value of

mg

lgives the spring constant K.

A graph is plotted taking mass along the X-axis and extension along the Y-axis. A straight line graph is obtained. From the graph, spring constant can be calculated. The unknown mass m' is suspended to the weight hanger and the

corresponding extension 'l is determined as before. Knowing the spring constant K

and the extension 'l , the mass of the body can be determined. The unknown mass

can be calculated from the graph also.

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Observations and Calculations

Pointer Reading

No Mass

suspended On loading

On unloading

Mean

Extension

l

Mass Producing Extension

m

K = mg

l

g cm cm cm cm g N m-1

1 Dead load m0

x0 =

2 m0 +

x1 =

x1 – x0 =

3 m0 +

x2 = x2 – x0 =

4 m0 +

x3 = x3 – x0 =

5 m0 +

x4 = x4– x0 =

6 m0 +

x5= x5 – x0 =

Mean K = N m-1

To find the unknown mass

Pointer Reading No Mass suspended

On loading On unloading Mean

Extension

'l

g cm cm cm cm

1 Dead load m0

x0 =

2 m0 +

unknown mass (m’)

x’=

x’– x0 =

Extension for unknown mass 'l = cm

= m

Unknown mass '

'Kl

mg

=

= = kg From graph, AB = g = kg BC = cm = m Spring constant K = AB x g BC = = N m

-1

Unknown mass from graph = g = kg Result Spring constant of the spring, (1) By calculation = N m

-1

(2) From graph = N m-1

Unknown mass (1) By calculation = kg (2) From graph = kg

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9. HELICAL SPRING II Aim To determine the spring constant of the given helical spring by the method of vertical oscillations Apparatus Helical spring apparatus, slotted weights, stop clock etc Principle

The period of vertical oscillation of a spring T when a mass M is suspended at its end is given by

2M

TK

π= K → Spring constant

Spring constant 2

2K= 4

M

Tπ

Procedure A known mass (M) is attached at the lower end of the spring. The Mass attached is slightly pulled down and released to execute vertical oscillations. The time taken for 20 oscillations is noted twice using a stop clock and their mean value (t) is found out. The period of oscillation T is

determined. Using M and T, 2

M

Tis calculated. The

experiment is repeated by increasing the mass and the mean

value of 2

M

Tis estimated. The spring constant of the spring is

calculated. A graph is drawn taking M along the X axis and T

2along the Y axis. The graph is a straight line. Spring constant can be calculated from the graph also.

Observations and Calculations

Time for 20 Oscillations

No Mass

suspended M 1 2 Mean (t)

Period

20

tT =

T2

2

M

T

Mean

2

M

T

kg s s s s s2 kg s

-2 kg s

-2

Spring constant 2

2K= 4

M

Tπ

= = Nm

-1

From Graph AB = kg BC = s

2

K = 24AB

BCπ

= = Nm

-1

Result Spring constant of the spring 1 By calculation = Nm

-1

2 From graph = Nm-1

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10. RESONANCE COLUMN I Aim 1 To find the velocity of sound in air at room temperature and hence to find the velocity of sound at 0

0 C.

2 To determine the unknown frequency of the given tuning fork. Apparatus

Resonance column apparatus filled with water, tuning forks, rubber hammer, metre scale, thermometer etc. Principle

If the first and second resonating lengths for a tuning fork of frequency n is 1l and 2l , the

velocity of sound at room temperature is given by

( )2 12tV n l l= −

Velocity of sound at 0 0C, Vo

=Vt - 0.6 t ( approx.) , when Vt is expressed in m/s

t → temperature in 0C.

If 1 'l and

2 'l represent first and second resonating lengths for a tuning fork of unknown fre-

quency n',

( )2 12 ' ' 'tV n l l= −

( )2 1

'2 ' '

tVnl l

=−

Procedure Determination of velocity of sound in air Length of the air column in the resonance column apparatus is reduced to minimum. A tuning fork of frequency n is excited and is kept near the mouth of the resonance tube. The length of the air column in the tube is slowly increased. At a particular length maximum

sound is heard. The length of the air column 1l is measured. Keeping

the vibrating tuning fork at the mouth of the tube, the length of the air

column is again increased to 2l to get maximum sound. The velocity

of sound in air at room temperature is calculated. The experiment is repeated with tuning forks of different frequencies and the mean value of Vt is determined. The room temperature t is measured using a thermometer. Knowing Vt and t, the velocity of sound in air at 0°C is calculated Determination of unknown frequency Using the given tuning fork, the first and second resonating lengths are determined. Knowing the velocity of sound at room temperature (Vt) and the resonating lengths, the unknown frequency of the tuning fork is calculated Observations and Calculations Determination of velocity of sound in air

First Resonance length ( 1l ) Second Resonance length ( 2l )

No

Frequency of

Tuning fork n

1 2 Mean 1 2 Mean

Velocity of sound Vt =

( )2 12n l l−

Hz cm cm cm cm cm cm cm/s

Mean Vt = cm/s Velocity of sound at room temperature Vt = m/s Room temperature (t) =

0C

Velocity of sound at 0 0C, Vo

= Vt - 0.6 t

= = m/s

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Determination of unknown frequency

First Resonance length (1' l ) Second Resonance length (

2 'l )

1 2 Mean 1 2 Mean

Unknown frequency

( )2 1

'2 ' '

tVnl l

=−

cm cm cm cm cm cm Hz

Result Velocity of sound in air at room temperature ( …….

0C ) = m/s

Velocity of sound in air at 0 0C = m/s

Unknown frequency of tuning fork = Hz

11. RESONANCE COLUMN II Aim To compare the frequencies of two tuning forks using resonance column and to find the end correction. Apparatus Resonance column apparatus filled with water, tuning forks, rubber hammer, metre scale etc Principle

If the first and second resonating lengths for a tuning fork of frequency n1 is 1l and

2l , the

velocity of sound at room temperature is given by

( )1 2 12tV n l l= −

If 1 'l and

2 'l are the first and second resonating lengths for another tuning fork of frequency n2

( )2 2 12 ' 'tV n l l= −

( )( )2 11

2 2 1

' 'l ln

n l l

−=

−

The end correction

2 13

2

l le

−= Or 2 1

' 3 '

2

l le

−=

Procedure Length of the air column in the resonance column apparatus is reduced to minimum. The tuning fork of frequency n1 is excited and is kept near the mouth of the resonance tube. The length of the air column in the tube is slowly increased. At a particular length maximum sound is heard. The length of the

air column 1l is measured. Keeping the vibrating tuning fork at the mouth of the tube, the length of the air

column is again increased to get maximum sound. The second resonating length 2l is determined.

Knowing 1l and 2l the end correction are calculated. The experiment is repeated with the second

tuning fork of frequency n2. The first and second resonating lengths 1 'l and

2 'l are determined. Using

1 'l and 2 'l the end correction are again calculated. Knowing the first and second resonating lengths

corresponding to the two tuning forks, ratio of their frequencies is also calculated Observations and Calculations

First Resonance length Second Resonance length Frequency of

Tuning fork 1 2 Mean 1 2 Mean

End correction

e

ratio of frequencies

( )( )2 11

2 2 1

' 'l ln

n l l

−=

−

Hz cm cm cm cm cm cm cm

n1

1l = 2l =

n2

1 'l = 2 'l =

Mean e = cm = m

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Result Ratio of frequencies = End correction = m

12. SONOMETER I

Aim 1 To establish the relation between frequency and length of a stretched string when the linear density of the string and tension in the string are constant. 2 To find the unknown frequency Apparatus The sonometer, tuning forks of different frequencies, slotted weights etc Principle When stationary waves are set up on a stretched string, the frequency of vibration

l→ Length of the wire segment in unison with the fork

T → tension in the string m → linear density of the string If n and T are kept constant

n x l = K, a constant

If L is the length of the wire segment in unison with the tuning fork of unknown frequency N N = K

L Procedure Suitable weight is attached to the free end of the sonometer wire passing over the knife edges and pulley. The movable knife edges are kept near to each other. A small paper rider is kept on the wire, in between the knife edges. The given tuning fork of known frequency n is excited and the stem is kept on the sonometer box. Distance between the knife edges is slowly increased. At a particular distance, the paper rider is just thrown off. This happens when the vibrating wire segment is in unison with the vibrating tuning fork. The length between the knife edges

( l ) is measured and n x l is calculated. Experiment is repeated

with tuning forks of different frequencies. In all the cases it is found

that n x l = a constant

A graph is plotted taking n along the X-axis and 1

lalong the

Y-axis. It is found to be a straight line. To find the unknown frequency

Mean value of n x l = K is calculated. Vibrating length of the

wire segment in unison with the tuning fork of unknown frequency (L) is noted. From this the unknown frequency of the tuning fork (N) can be calculated using the relation N = K L The unknown frequency can be calculated from the graph also. Observations and Calculations

Length in unison with the fork ( l ) No Frequency

1 2 Mean K = n x l

1

l

Hz cm cm cm Hz cm cm -1

Mean K = Hz cm

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To find unknown frequency

Length in unison with the fork (L)

1 2 Mean

N = K L

1

L

cm cm cm Hz cm -1

Result 1 The relation between the frequency and length of a stretched string is established

n x l = a constant.

1

nl

− graph is a straight line

2 Unknown frequency of the tuning fork (i) by calculation = Hz (ii) from graph = Hz

13. SONOMETER II Aim To establish the relation between length and tension of a stretched string with uniform linear density for a constant frequency using sonometer Apparatus

Sonometer, tuning fork, slotted weights etc Principle When stationary waves are set up on a stretched string, the frequency of vibration

l→ Length of the wire segment in unison with the fork

T → tension in the string m → linear density of the string

If n and m are kept constants, 2

T

l = constant

T = Mg

2

Mg

l = constant

2

M

l = constant

Procedure

Suitable mass M is attached at the free end of the sonometer wire. The bridges are brought close to each other. A paper rider is placed at the mid point of the wire segment between the knife edges. A tuning fork of known frequency is excited and placed on the sonometer box. The distance between the knife edges is adjusted till the wire segment vibrates in unison with the fork. At this

time the paper rider will be thrown off. The length l of the

wire segment is measured. 2

M

lis calculated. The

experiment is repeated for different masses and the

mean value of 2

M

lis calculated. A graph is plotted

taking M along the X-.axis and 2l along the Y-axis. The graph is found to be a straight line.

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Observations and Calculations

Length in unison with the fork ( l ) No

Mass Suspended

M 1 2 Mean 2l 2

M

l

kg cm cm cm cm2 kg cm

-2

Mean 2

M

l = kg cm

-2

Result The relation between the length and tension for constant frequency is established

2

M

l = a constant

M - 2l graph is a straight line

SECTION B

14. OHM’S LAW Aim

To verify Ohm's law and hence to find the resistivity of the material of the given wire. Apparatus

Ammeter, voltmeter, battery, rheostat, key, the given resistance wire, screw gauge etc. Principle According to Ohm's law, at constant

temperature the current flowing through a

conductor is directly proportional to the

potential difference across its ends.

VR

I= , the resistance of the conductor.

If R is the resistance of a wire having

length l and radius r, the resistivity of the

material of the wire is given by

2r R

l

πρ =

Procedure

Connections are made as shown in the figure. The circuit is switched on and the current is fixed at a certain value with the help of the rheostat. Corresponding voltage is noted. The ratio of voltage to current is calculated. The experiment is repeated for different currents and the mean value of resistance is obtained. The radius of the wire is measured using a screw gauge and the length using a meter scale. Hence the resistivity of the material of the wire is calculated.

A graph is plotted with I along the X-axis and V

along the Y-axis. Slope of the graph gives the resistance of the conductor

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19

. Observations and Calculations

No

Current

I

Voltage V

ResistanceV

RI

= Mean R

A V Ω Ω

From graph, AB = A BC= V

R = BC

AB

=

= Ω To find radius of the wire Distance moved for 5 rotations = mm Pitch = Distance moved for 5 rotations 5 = = mm Least Count (L C) = Pitch . No. of divisions on the head scale = = mm Zero Coincidence = Zero correction = div

No PSR HSR Corrected

HSR

Total Reading = PSR + (corrected HSR x

LC) Mean

mm mm mm

Mean diameter of the wire = m

Radius of the wire (r) = m

Length of the wire ( l ) = cm

= m

Resistivity

2r R

l

πρ =

=

= mΩ

Result Resistance of the given wire

By Calculation = Ω

From graph = Ω

Resistivity of the material of the given wire = mΩ

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20

15. METRE BRIDGE I Aim To determine the resistance and hence the resistivity of the given wire using metre bridge Apparatus Metre Bridge, battery, key, resistance box, resistance wire, galvanometer, high resistance screw gauge etc. Principle

If R is the resistance in the resistance box and l is the balancing length from the side of

unknown resistance, by Wheatstone’s principle

100

X l

R l=

−

100

R lX

l=

−

Resistivity of the material of the wire is given

by

2r X

L

πρ =

r - Radius of the wire L - length of the wire

Procedure Connections are made as shown in the figure with the unknown resistance X in the left gap and the resistance box in the right gap. To check the circuit a suitable resistance R is introduced in the resistance box and the key K is closed. The jockey is pressed at the ends of the wire AB. If the deflections in the galvanometer are in opposite directions the circuit is correct. The jockey is moved along the wire AB till the galvanometer shows zero deflection. Then the point of the wire in contact with

the jockey is the balancing point. The balancing length AJ is noted as 1l . The resistance R and X are

interchanged and the balancing length BJ is noted as 2l . The mean balancing length l is calculated

and the unknown resistance X is determined. The experiment is repeated for different values of R and the mean value of the unknown resistance X is calculated. The radius of the wire is determined using the screw gauge. The length L of the wire is measured using a metre scale. The resistivity of the material of the wire is calculated. Observations and Calculations

Balancing length when X is

No Resistance

R In the left gap

1l

In the right gap

2l

1 2

2

l ll

+=

100

R lX

l=

−

Ω cm cm cm Ω

Mean X = Ω

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21

To find the radius of the wire Distance moved for 5 rotations = mm Pitch = Distance moved for 5 rotations 5 = = mm Least Count (L C) = Pitch . No. of divisions on the head scale = = mm Zero Coincidence = Zero correction = div

No PSR HSR Corrected

HSR

Total Reading = PSR + (corrected HSR x

LC) Mean

mm mm mm

Mean diameter of the wire = m Radius of the wire (r) = m Length of the wire (L) = cm = m

Resistivity

2r X

L

πρ =

=

= mΩ

Result

Resistance of the given wire = Ω

Resistivity of the material of the given wire = mΩ

16. METRE BRIDGE II Aim

To verify the laws of combination (series and parallel) of resistances using metre bridge Apparatus Metre Bridge, two resistance wires, resistance box, galvanometer, high resistance, battery, plug key etc. Principle If R is the resistance in the resistance box and

l is the balancing length from the side of unknown

resistance, by Wheatstone’s principle

100

R lX

l=

−

When two resistances X1 and X2 are connected in series, the effective resistance

1 2seriesX X X= +

When they are connected in parallel

1 2

1 2

parallel

X XX

X X=

+

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22

Procedure Connections are made as shown in figure. The first resistance wire X1 is connected in the left gap and resistance box R in the right gap. A suitable resistance R is introduced in the

resistance box. The balancing length1l is measured. By interchanging X1 and R in the gaps,

balancing length 2l also is measured. The mean balancing length l is calculated. Hence X is

calculated. The experiment is repeated for different values of R and the mean value of X1 is calculated. X1 is replaced by X2 in the circuit and the mean value of X2 is also determined. To determine the effective resistance of series combination X1 and X2 are joined end to

end (in series). The mean balancing length is calculated by measuring 1l and

2l . HenceseriesX is

determined. X1 and X2 are joined in parallel. The mean value of effective resistance parallelX is

determined.Theoretical values ofseriesX and parallelX are calculated and are compared with the experi-

mental values Observations and Calculations

Balancing length when X is Mode of

connection of unknown resistance

No

Resistance R

In the left gap

1l

In the right gap

2l

1 2

2

l ll

+=

100

R lX

l=

− Mean X

Ω cm cm cm Ω Ω

X1 alone

X2 alone

X1 and X2 in series

X1 and X2

in parallel

Resistance of the first wire X1 = Ω

Resistance of the second wire X2 = Ω

Theoretical value of 1 2seriesX X X= +

=

= Ω

Experimental value of seriesX = Ω

Theoretical value of 1 2

1 2

p a r a l le l

X XX

X X=

+

=

= Ω

Experimental value parallelX = Ω

Result

Effective resistance in series combination

Theoretical value = Ω

Experimental value = Ω Effective resistance in parallel combination

Theoretical value = Ω

Experimental value = Ω Hence the laws of combination of resistances verified

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23

1 1

2 2

E l

E l=

17. POTENTIOMETER I Aim To compare the emfs of the given two primary cells using potentiometer Apparatus

Potentiometer, rheostat, two way key, battery, galvanometer, the given cells, high resistance

etc

Principle

When a steady current is

maintained in the potentiometer

wire, the emf is directly proportional

to the balancing length.

If the balancing lengths of

the two cells having emfs 1E and 2E

are 1l and 2l , then

1 1

2 2

E l

E l=

Procedure Connections are made as shown in the figure. The potentiometer wire in series with the accu-mulator and rheostat forms the primary circuit. The primary circuit is closed. One of the cells is introduced in the secondary circuit with the help of a two way key. The jockey is moved along the potentiometer wire to get zero deflection in the galvanometer. The length of the wire from the common point A and to the position of the jockey is measured. This gives the balancing length of the first cell. Changing the key plug to the other slot the second cell is put in the secondary circuit. As above the balancing length of the second cell is also determined. The ratio of these balancing lengths gives the ratio of their emfs. The experiment is repeated by adjusting the rheostat. Observations and Calculations

Balancing length for

No

Leclanche cell (1E )

1l

Daniel cell (2E )

2l

Mean 1

2

E

E

cm cm

Result The ratio of the emfs of the given primary cells =

18. POTENTIONMETER II Aim To determine the internal resistance of the given primary cell using potentiometer Apparatus Potentiometer, battery, given primary cell (Leclanche Cell), rheostat, galvanometer, resistance box, high resistance, plug keys etc

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24

Principle

If 1l is the balancing length when no current is drawn from the cell

1E l∝

If 2l is the balancing length when the

cell is in a closed circuit with an external resistance R

2

ERl

R r∝

+

From the two equations,

Internal resistance 1 2

2

( )R l lr

l

−=

Procedure

The primary circuit is closed. Keeping the key K1 open the balancing length 1l is measured. A

suitable resistance R is introduced in the resistance box. The key K1 is closed and the balancing

length 2l is measured. Hence the internal resistance is calculated. The experiment is repeated for

different values of R and in each case internal resistance is calculated. Observations and calculations

Balancing length

No Resistance

R When K1 is open

1l

When K1 is closed

2l

1 2

2

( )R l lr

l

−=

Ω cm cm Ω

Result The internal resistance of the ………………... cell is determined for different values of external

resistance. Value of internal resistance lies between ………….Ω and ………….Ω .

19. GALVANOMETER –Resistance and Figure of Merit Aim

To determine the resistance of a galvanometer by half deflection method and hence to find the figure of merit of the galvanometer Apparatus

Galvanometer, resistance boxes, battery, commutator etc.

Principle Let d the deflection in the galvanometer of resistance G when a current

I flows through it. When a resistance (R) equal to the resistance of the galvanometer is connected in series with G the current becomes

2

Iand the deflection becomes

2

d

Figure of merit of the Galvanometer

1

E P

KP Q G d

=+

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25

Procedure

The connections are made as in figure. A high resistance is introduced in Q and a small resistance in P

Resistance in R is kept zero. The circuit is closed. Number of divisions deflected by the galvanometer

needle towards one side (d) is noted. A suitable resistance is introduced in R so that the deflection

becomes2

d.

Now R = G. The direction of current is reversed using commutator. The deflection on the

other side is noted and the value of R required for half deflection is determined again. Mean value of the

resistance of the galvanometer (G) is calculated. Figure of merit of the galvanometer is calculated. The

experiment is repeated for different values of P and Q.

Observations and Calculations

E.m.f. of the cell = V

Deflection in galvanometer

d

Resistance in R for half

Deflection, G No Resistance

P Resistance

Q Left Right Mean Left Right Mean

Figure of merit

1

E PK

P Q G d=

+

Ω Ω Ω Ω Ω A / div

Mean G = Ω

Mean K = A / div

Result

Resistance of the galvanometer G = Ω

Figure of merit K = A / div

20. P- N JUNCTION DIODE Aim To draw the characteristics of a semiconductor diode and hence to determine its knee voltage static resistance and dynamic resistance Apparatus A p-n junction diode, rheostat, voltmeter, milliammeter, DC source etc Principle A diode conducts when it is forward biased. A negligible current is observed up to the knee voltage and thereafter current increases sharply with voltage Static resistance (d c resistance)

f

dc

f

VR

I=

Dynamic resistance (ac resistance)

f

ac

f

VR

I

∆=∆

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26

Procedure

The connections are made as shown in figure. The potential difference ( fV ) across the diode

is increased gradually in steps with the help of potential divider arrangement. The forward current

(fI ) are noted in each case. The ratio

f

f

V

I is calculated in each case. It is found that the static

resistance dcR varies with the current

A graph is drawn with forward voltage fV

along the X-axis and forward current fI along the

Y axis. The graph is the forward characteristic curve of the diode. The forward current increases sharply at a particular value of forward voltage known as knee voltage. Knee voltage Vk is noted. To determine the dynamic resistance two points A and B are marked on the curve above the bent

portion. The change in voltage fV∆ and change

in current fI∆ are determined from the graph and

the dynamic resistance is calculated Observations and Calculations Least count of the voltmeter = V Least count of the milliammeter = mA

No Forward Voltage

fV

Forward Current

fI

Static Resistance

f

dc

f

VR

I=

V mA Ω

From graph,

Knee Voltage (Vk ) = V

fV∆ = AB = V

fI∆ = BC = mA= A

Dynamic resistance (ac resistance) f

ac

f

VR

I

∆=∆

=

= Ω Result

The characteristic curve for a forward biased diode is drawn Static resistance of the diode for different currents are tabulated

Dynamic resistance of the diode = Ω

Knee voltage (Vk ) = V

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27

21. MAPPING OF MAGNETIC FIELD – I (North Pole Pointing South)

Aim To map the combined magnetic field of earth and that of a bar magnet placed along the magnetic meridian with its north pole pointing south and hence to find the moment and pole strength of the magnet Apparatus Bar magnet, compass needle, drawing board, etc Principle

At the null points the horizontal component of the earth’s magnetic field Bh is equal and

opposite to the field due to the magnet

( )0

22 2

2

4h

mdB

d l

µπ

=−

Moment of the magnet

( )22 2

0

4

2h

d lm B

d

πµ

−= 0µ → Permeability of free space =

7 14 x 10 Hmπ − −

2d → Distance between the null points

2l→ Length of the magnet

40.38 10hB T−= ×

( )22 2190 d l

md

−=

Pole strength of the magnet 2

mp

l=

Procedure The bar magnet is placed symmetrically with its axis along the magnetic meridian with its north pole pointing geographic south. Its outline is drawn and the poles are marked. A point is marked near the north pole of the magnet. The magnetic needle is placed with its south pole above the point.The other end of the compass needle is marked. The magnetic needle is moved so that its south pole is against the point. A new point is marked against the north pole of needle and the process is repeated till the magnetic needle reaches the south pole of the magnet. Earth’s line of force is also drawn. To locate the null points, the compass needle is moved slowly along the axial line. At the null points the needle just begins to rotate. The trace of the needle is

taken. The distance ( 2d ) between the null points and the

length of the magnet ( 2l ) are measured. Knowing Bh, the moment and the pole strength

of the magnet can be calculated. Observations and Calculations

Length of the magnet 2l = cm

= m

l = m

Distance between the null points 2d = cm

= m

d = m

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28

Dipole moment of the magnet ( )22 2190 d l

md

−=

= = Am

2

Pole strength of the magnet 2

mp

l=

= = Am Result

The combined magnetic field is plotted and the null points are located Dipole moment of the magnet = Am

2

Pole strength of the magnet = Am

22. MAPPING OF MAGNETIC FIELD – II (North Pole Pointing North)

Aim To map the combined magnetic field of earth and that of a bar magnet placed along the magnetic meridian with its north pole pointing north and hence to find the moment and pole strength of the magnet Apparatus Bar magnet, compass needle, drawing board, etc Principle

At the null points the horizontal component of the earth’s magnetic field Bh is equal and

opposite to the field due to the magnet

( )0

32 2 24

h

mB

d l

µπ

=+

Moment of the magnet

( )3

2 2 2

0

4h

m d l Bπµ

= + 0µ → Permeability of free space =7 14 x 10 Hmπ − −

2d → Distance between the null points

2l→ Length of the magnet

40.38 10hB T−= ×

( )3

2 2 2380m d l= +

Pole strength of the magnet 2

mp

l=

Procedure

Setting up of the drawing board and drawing of axial and equitorial lines are done. The bar magnet is placed with its north pole pointing geographic north. Its outline is drawn and the poles are marked. The magnetic lines of forces of the magnet and the earth are drawn. To locate the null points, the magnetic needle is moved slowly from the centre of the magnet along the equitorial line. The null points are located and moment and pole strength are calculated

Practical Physics

29

Observations and Calculations

Length of the magnet 2l = cm

= m

l = m

Distance between the null points 2d = cm

= m

d = m

Dipole moment of the magnet ( )3

2 2 2380m d l= +

= = Am

2

Pole strength of the magnet 2

mp

l=

= = Am Result The combined magnetic field is plotted and the null points are located Dipole moment of the magnet = Am

2

Pole strength of the magnet = Am

23. CONCAVE MIRROR Aim To determine the focal length of the given concave mirror

1. By distant object method 2. By normal reflection method 3. By u-v method 4. From u-v graph

5. From 1 1

u v− graph

Apparatus Concave mirror, mirror stand, illuminated wire gauze, screen, metre scale etc Principle Distant object method

When the object is at infinity, the image is formed at the principal focus. The distance between the mirror and the screen gives the focal length. Normal reflection method (Normal incidence method) When the object is at the centre of curvature of the concave mirror, image is formed at the same position. The distance between the mirror and the object gives the radius of curvature (R) of the mirror

Focal length 2

Rf =

u-v method If u is the object distance and v the image distance

uv

fu v

=+

u-v graph

4

OA OBf

+= OA and OB are the co-ordinates when u = v

1 1

u v− graph

2

fOA OB

=+

OA and OB are the intercepts on the X and Y axes

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30

Procedure Distant object method

The concave mirror is turned towards a distant object. The screen is placed in front of the mirror. The position of the screen is adjusted till a clear image is formed on it. The distance between the centre of the mirror stand and the screen gives the focal length. The experiment is repeated and the mean focal length is calculated. Normal Reflection method (Normal incidence method) The concave mirror is placed in front of the illuminated wire gauze and its position is adjusted so that a clear image of the wire gauze is formed by the side of the illuminated wire gauze. The distance between the mirror and the wire gauze gives the radius of curvature R. The experiment is repeated and the mean value of focal length is calculated. u-v method

The concave mirror is placed in front of the illuminated wire gauze at a distance (u) greater than the focal length of the mirror. A screen is placed in front of the mirror and its position is adjusted to get a clear image on it. The distance (v) between the mirror and the screen is measured. The focal length is calculated. The experiment is repeated and the mean focal length is calculated u-v graph A graph is plotted with u along X axis and v along Y axis taking the same scale for both the axes. A bisector is drawn which meets the graph at C. From the graph OA = OB = 2f. Hence focal

length 4

OA OBf

+=

1 1

u v− graph

A graph is plotted with 1

u

along X-axis and

1

v

along Y-axis

taking same scale for both the axes. The graph intercepts the X axis at A and Y axis at B. Focal length is calculated using the relation

2f

OA OB=

+

Observations and Calculations Distant Object method

No Distance between the mirror and the image

Mean focal length f Mean f

cm cm m

Normal Reflection method

No Distance between

the mirror and object R

Focal length

2

Rf =

Mean focal length f Mean f

cm cm cm m

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31

u-v method

No

Distance between the object and the mirror

u

Distance between the image and the mirror

v

Focal length

uvf

u v=

+

Mean focal length f

1

u

1

v

cm cm cm cm cm -1

cm -1

Mean focal length f = m

From u-v graph, OA = cm OB = cm

4

OA OBf

+=

= = cm = m

From 1 1

u v− graph,

OA = cm

-1 OB = cm

-1

2

fOA OB

=+

= = cm = m Result Focal length of the concave mirror

1 By distant object method = m 2 By normal reflection method = m 3 By u-v method = m 4 From u-v graph = m

5 From 1 1

u v− graph = m

24. CONVEX LENS Aim To determine the focal length of the given convex lens

1 By distant object method 2 By u-v method 3 From u-v graph

4 From 1 1

u v− graph

Apparatus Convex lens, lens stand, illuminated wire gauze, screen, metre scale etc Principle Distant object method When the object is at infinity, the image is formed at the principal focus. The distance between the lens and the screen gives the focal length.

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32

u-v method If u is the object distance and v the image distance

uv

fu v

=+

u-v graph

4

OA OBf

+= OA and OB are the co-ordinates when u = v

1 1

u v− graph

2

fOA OB

=+

OA and OB are the intercepts on the X and Y axes

Procedure Distant object method The convex lens is turned towards a distant object. The screen is placed on the other side of the lens. The position of the screen is adjusted till a clear image is formed on it. The distance between the centre of the lens stand and the screen gives the focal length. The experiment is repeated and the mean focal length is calculated. u-v method The convex lens is placed in front of the illuminated wire gauze at a distance (u) greater than the focal length of the mirror. A screen is placed on the other side of the lens and its position is adjusted to get a clear image on it. The distance (v) between the lens and the screen is measured. The focal length is calculated. The experiment is repeated and the mean focal length is calculated u-v graph A graph is plotted with u along X axis and v along Y axis taking the same scale for both the axes. A bisector is drawn which meets the graph at C. From the graph OA = OB = 2f. Hence focal

length 4

OA OBf

+=

1 1

u v− graph

A graph is plotted with 1

u

along X-axis and

1

v

along Y-axis

taking same scale for both the axes. The graph intercepts the X axis at A and Y axis at B. Focal length is calculated using the relation

2f

OA OB=

+

Observations and Calculations Distant Object method

No Distance between the lens

and the image Mean focal length f Mean f

cm cm m

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33

u-v method

No

Distance between the object and the lens u

Distance between the image and

the lens v

Focal length

uvf

u v=

+

Mean focal length f

1

u

1

v

cm cm cm cm cm -1

cm -1

Mean focal length f = m

From u-v graph, OA = cm OB = cm

4

OA OBf

+=

= = cm = m

From 1 1

u v− graph,

OA = cm -1

OB = cm -1

2

fOA OB

=+

= = cm = m Result Focal length of the convex lens

1 By distant object method = m 2 By u-v method = m 3 From u-v graph = m

4 From 1 1

u v− graph = m

25. CONVEX MIRROR

Aim

To determine the focal length of a convex mirror using a convex lens Apparatus

Convex mirror, convex lens, screen, illuminated wire gauze, metre scale, lens stand etc Principle When light rays fall normally on a convex mirror, it reflects the rays along the same path. So the image is obtained side by side with the object. If R is the radius of curvature of the convex mirror,

Focal length 2

Rf =

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34

Procedure The convex lens is mounted on a stand in front of illuminated wire gauze. A screen is placed on the other side and its position is adjusted to get a clear magnified image of the wire gauze on it. The given convex mirror is introduced in between the convex lens and the screen with its reflecting surface towards the lens. The position of the mirror is adjusted to get the image of the wire gauze side by side with the wire gauze itself. The distance between the mirror and the screen gives the radius of curvature (R) of the convex mirror. Focal length of the mirror is calculated. The experiment is repeated by changing the distance between the wire gauze and the lens and in each case focal length is calculated. Observations and Calculations

No Distance between the screen and the

mirror R Mean R

Focal length

2

Rf =

cm cm cm

Focal length of the convex mirror = m Result

Focal length of the given convex mirror = m

26. REFRACTION THROUGH A PRISM

Aim

1 To study the variation of the angle of deviation (d) with the angle of incidence (i) and to find the angle of minimum deviation (D).

2 To find out the refractive index of the material of the prism Apparatus

Glass prism, Drawing board, Pins, Protractor, etc Principle The refractive index of the material of the prism is given by

2

2

A DSin

nA

Sin

+ = A→ Angle of prism

D→ Angle of minimum deviation

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35

Procedure A paper is fixed on the drawing board. The outline ABC of the prism is marked on the paper. The prism is removed and normal N1N2 is drawn to the face AB at the point Q. Another line PQ is drawn at Q making an angle i with normal N1N2.Two pins P1 and P2 are fixed on this line. The prism is replaced on the outline ABC. Viewing the pins from the face AC of the prism, two other pins Q1 and Q 2 are fixed so that P1, P2, Q1 and Q 2 are in a line. The pins are removed. A line RS is drawn to meet on AC through the marks of Q1 and Q 2

. The line QR is joined. PQ and RS are produced to meet at E. The angle FER is the angle

of deviation (d). The experiment is repeated for different values of angle of incidence and the corresponding angles of deviations are measured. A graph is drawn with angle of incidence i along the X-axis and the angle of deviation d along the Y-axis. The angle of deviation corresponding to the lowest bend of the curve is the angle of minimum deviation D. Knowing the angle of prism, the refractive index of the material of the prism can be calculated.

Observations and Calculations

No Angle of incidence

i Angle of deviation

d

degree degree

Angle of minimum deviation D (From graph) = Angle of the prism A = Refractive index of the material of the prism,

2

2

A DSin

nA

Sin

+ =

= = Result

The variation of angle of deviation with angle of incidence is shown graphically. Angle of minimum deviation D = Refractive index of the material of the prism =

27. REFRACTIVE INDEX OF GLASS Aim

To determine the refractive index of the material of a glass slab using a travelling microscope.

Apparatus

Glass slab of known thickness, white paper, Travelling Microscope etc Principle

Refractive index of the material of glass slab

actual depthn

apparent depth=

Practical Physics

36

Procedure Least count (LC) of the travelling microscope is determined. A black dot is put on a white paper and is placed on the plane of the travelling microscope. By adjusting the microscope the dot is focussed well. The main scale reading (MSR) and vernier scale reading (VSR) on the vertical scale are noted. The total reading a = MSR + (VSR x LC) is calculated. The glass slab is placed on the black dot. The image in the microscope becomes blurred due to the apparent shift of the dot. By adjusting the tangential screw, the vertical scale is raised to focus the dot again. The MSR and VSR are again noted. The total reading b = MSR + (VSR x LC) is calculated. The difference in the readings gives the apparent shift (x). By changing the position of the glass slab, through which the dot is observed, the experiment is repeated. Mean value of x is determined. Actual depth = thickness of glass slab (h). Apparent depth = (h-x). Hence the reflective index is calculated. Observations and Calculations Value of one main scale division (MSD) of the microscope = mm = cm Number of divisions on the vernier scale (n) = Least count (LC) = 1 MSD n = = cm Observations and Calculations

Reading of the black dot Reading of the shifted dot No

MSR VSR Total a = MSR+(VSR x LC)

MSR VSR Total b = MSR+(VSR x LC)

Apparent Shift x=a-b

Mean shift

x

cm cm cm cm cm cm

Actual depth (thickness of glass slab) h = cm Mean shift x = cm Apparent depth = h – x = = cm

Refractive index of the material of glass slab

actual depthn

apparent depth=

= h

h x−

= = Result Refractive index of the material of the glass slab =