book page 84 87 syllabus2.12 2 - wordpress.com •describe how resistance varies with conditions for...

Special resistors Book page 84 ndash 87

Syllabus212 ndash 213

copycgrahamphysicscom 2016

Multiple-choice quiz


What am I

LDR LED or thermistor


Starter

LDRrsquos and thermistors are both types of resistor which can change their resistances

What change in conditions do you think might cause each to change its resistance


Aim bull Describe how resistance varies with conditions for

LDRrsquos and thermistors and how this can be investigated experimentally

Key words

bull LDR (Light Dependent Resistor) 조명 의존형 저항기 - diode

bull Thermistor 서미스터 저항기

bull Conditions 상태 조건


How do street lights automatically switch on and off

Have you ever wondered

The big picture


What is a diode A diode is a component made

from a semiconducting material

such as silicon

Diodes have the unique

property of only allowing

current to pass through them

in one direction

Some diodes emit light when they

conduct electricity These are called

Light Emitting Diodes (LEDs)

The arrowhead on the symbol

shows the direction of current flow

diode and its symbol

LDRs LEDs and Thermistors copycgrahamphysicscom 2016

The resistance of a light

dependent resistor (LDR)

is not fixed It is dependent

on the intensity of incident light

res

ista

nc

e (k

)

light intensity

LDRs light and resistance

An LDR has a high

resistance in the dark but a

low resistance in the light

This means that LDRs can be

used in light sensing circuits

because their output is dependent

on the light conditions

The graph shows how the

resistance of an LDR decreases

as the light intensity increases

LDR symbol


The resistance of a

thermistor varies

depending on temperature

Thermistors temperature and resistance

This is unusual as resistance

normally increases with

increasing temperature

Thermistors are useful in the

sensor circuits of a

thermostat as their output

varies with temperature

fluctuations

It has a high resistance

when cold but a low

resistance when hot

res

ista

nc

e (k

)

temperature (degC)

thermistor

symbol


LDR Task You have - 1 LDR - An ammeter - Power packs and wires - 3 pieces of paper of known thickness I have 3 pieces of paper of unknown thickness You need to tell me Easy How the resistance of an LDR changes with light level Harder The thicknesses of my pieces of paper


Thermistor Task You have - 1 Thermistor - An ammeter - Power packs and wires - 3 containers of water at known temperatures I have a glass of water of unknown temperature You need to tell me Easy How the resistance of a thermistor changes with

temperature Harder The temperature of my water


Light Dependent Resistor LDR Its resistance decreases as the light intensity increases (The higher the illumination the higher the current

Temperature Dependent Resistor Thermistor Its resistance decreases as the temperature increases (The higher the temperature the higher the current)

Thermistors and LDRs can work as Sensors A sensor is a component that allows a physical quantity to change its resistance and hence control the amount of current flowing in a circuit

A

In this circuit the LDR can work as a lightmeter The higher the ammeter reading the higher the illumination

A

In this circuit the thermistor can work as a thermometer The higher the ammeter reading the higher the temperature


Summary

bull Thermistors have a resistance that decreases with increasing temperature

bull Resistance of an LDR decreases as greater levels of light fall on it


1 Match the follow electrical symbols for components with their names

cell power supply filament lamp switch fixed resistor voltmeter

2 Draw the symbols for the following components a) LDR b) variable resistor c) thermistor d) ammeter

3 As the intensity (brightness) of the light increases the resistance of the LDR _________________

4 As the temperature increases the resistance of the thermistor _________________

Plenary Resistance of LDR and thermistor

increases decreases

increases decreases

A

V


Resistor quiz


A

B

C

Circuit 1

which bulb will light up (notice the position of the diodes)


A

B

C

answer

Circuit 1

A amp B only


A

B

C

Circuit 2



A

B

C

answer

Circuit 2

None of them


A

B

C

Circuit 3



A

B

C

answer

Circuit 3

A amp C only


Key words bull LDR (Light Dependent Resistor) ndash A type of variable

resistor that is sensitive to light intensity As light intensity increases its resistance decreases

bull Diode ndash A resistor that only allows current to flow through it in one direction

bull Thermistor ndash A type of variable resistor that is sensitive to temperature As temperature increases its resistance decreases

bull Conditions ndash an event will happen if some other thing is taken place If temperature increases (condition) then resistance will decrease (thing taken place)


Multiple-choice quiz


What am I



Starter






Key words







The big picture




such as silicon




in one direction












res

ista

nc

e (k

)

light intensity


An LDR has a high










LDR symbol


The resistance of a

thermistor varies










fluctuations


when cold but a low

resistance when hot

res

ista

nc

e (k

)

temperature (degC)

thermistor

symbol










A


A



Summary










increases decreases

increases decreases

A

V


Resistor quiz


A

B

C

Circuit 1



A

B

C

answer

Circuit 1

A amp B only


A

B

C

Circuit 2



A

B

C

answer

Circuit 2

None of them


A

B

C

Circuit 3



A

B

C

answer

Circuit 3

A amp C only








What am I



Starter






Key words







The big picture




such as silicon




in one direction












res

ista

nc

e (k

)

light intensity


An LDR has a high










LDR symbol


The resistance of a

thermistor varies










fluctuations


when cold but a low

resistance when hot

res

ista

nc

e (k

)

temperature (degC)

thermistor

symbol










A


A



Summary










increases decreases

increases decreases

A

V


Resistor quiz


A

B

C

Circuit 1



A

B

C

answer

Circuit 1

A amp B only


A

B

C

Circuit 2



A

B

C

answer

Circuit 2

None of them


A

B

C

Circuit 3



A

B

C

answer

Circuit 3

A amp C only








Starter






Key words







The big picture




such as silicon




in one direction












res

ista

nc

e (k

)

light intensity


An LDR has a high










LDR symbol


The resistance of a

thermistor varies










fluctuations


when cold but a low

resistance when hot

res

ista

nc

e (k

)

temperature (degC)

thermistor

symbol










A


A



Summary










increases decreases

increases decreases

A

V


Resistor quiz


A

B

C

Circuit 1



A

B

C

answer

Circuit 1

A amp B only


A

B

C

Circuit 2



A

B

C

answer

Circuit 2

None of them


A

B

C

Circuit 3



A

B

C

answer

Circuit 3

A amp C only










Key words







The big picture




such as silicon




in one direction












res

ista

nc

e (k

)

light intensity


An LDR has a high










LDR symbol


The resistance of a

thermistor varies










fluctuations


when cold but a low

resistance when hot

res

ista

nc

e (k

)

temperature (degC)

thermistor

symbol










A


A



Summary










increases decreases

increases decreases

A

V


Resistor quiz


A

B

C

Circuit 1



A

B

C

answer

Circuit 1

A amp B only


A

B

C

Circuit 2



A

B

C

answer

Circuit 2

None of them


A

B

C

Circuit 3



A

B

C

answer

Circuit 3

A amp C only










The big picture




such as silicon




in one direction












res

ista

nc

e (k

)

light intensity


An LDR has a high










LDR symbol


The resistance of a

thermistor varies










fluctuations


when cold but a low

resistance when hot

res

ista

nc

e (k

)

temperature (degC)

thermistor

symbol










A


A



Summary










increases decreases

increases decreases

A

V


Resistor quiz


A

B

C

Circuit 1



A

B

C

answer

Circuit 1

A amp B only


A

B

C

Circuit 2



A

B

C

answer

Circuit 2

None of them


A

B

C

Circuit 3



A

B

C

answer

Circuit 3

A amp C only










such as silicon




in one direction












res

ista

nc

e (k

)

light intensity


An LDR has a high










LDR symbol


The resistance of a

thermistor varies










fluctuations


when cold but a low

resistance when hot

res

ista

nc

e (k

)

temperature (degC)

thermistor

symbol










A


A



Summary










increases decreases

increases decreases

A

V


Resistor quiz


A

B

C

Circuit 1



A

B

C

answer

Circuit 1

A amp B only


A

B

C

Circuit 2



A

B

C

answer

Circuit 2

None of them


A

B

C

Circuit 3



A

B

C

answer

Circuit 3

A amp C only












res

ista

nc

e (k

)

light intensity


An LDR has a high










LDR symbol


The resistance of a

thermistor varies










fluctuations


when cold but a low

resistance when hot

res

ista

nc

e (k

)

temperature (degC)

thermistor

symbol










A


A



Summary










increases decreases

increases decreases

A

V


Resistor quiz


A

B

C

Circuit 1



A

B

C

answer

Circuit 1

A amp B only


A

B

C

Circuit 2



A

B

C

answer

Circuit 2

None of them


A

B

C

Circuit 3



A

B

C

answer

Circuit 3

A amp C only








The resistance of a

thermistor varies










fluctuations


when cold but a low

resistance when hot

res

ista

nc

e (k

)

temperature (degC)

thermistor

symbol










A


A



Summary










increases decreases

increases decreases

A

V


Resistor quiz


A

B

C

Circuit 1



A

B

C

answer

Circuit 1

A amp B only


A

B

C

Circuit 2



A

B

C

answer

Circuit 2

None of them


A

B

C

Circuit 3



A

B

C

answer

Circuit 3

A amp C only
















A


A



Summary










increases decreases

increases decreases

A

V


Resistor quiz


A

B

C

Circuit 1



A

B

C

answer

Circuit 1

A amp B only


A

B

C

Circuit 2



A

B

C

answer

Circuit 2

None of them


A

B

C

Circuit 3



A

B

C

answer

Circuit 3

A amp C only








Summary










increases decreases

increases decreases

A

V


Resistor quiz


A

B

C

Circuit 1



A

B

C

answer

Circuit 1

A amp B only


A

B

C

Circuit 2



A

B

C

answer

Circuit 2

None of them


A

B

C

Circuit 3



A

B

C

answer

Circuit 3

A amp C only














increases decreases

increases decreases

A

V


Resistor quiz


A

B

C

Circuit 1



A

B

C

answer

Circuit 1

A amp B only


A

B

C

Circuit 2



A

B

C

answer

Circuit 2

None of them


A

B

C

Circuit 3



A

B

C

answer

Circuit 3

A amp C only








Resistor quiz


A

B

C

Circuit 1



A

B

C

answer

Circuit 1

A amp B only


A

B

C

Circuit 2



A

B

C

answer

Circuit 2

None of them


A

B

C

Circuit 3



A

B

C

answer

Circuit 3

A amp C only








A

B

C

Circuit 1



A

B

C

answer

Circuit 1

A amp B only


A

B

C

Circuit 2



A

B

C

answer

Circuit 2

None of them


A

B

C

Circuit 3



A

B

C

answer

Circuit 3

A amp C only








A

B

C

answer

Circuit 1

A amp B only


A

B

C

Circuit 2



A

B

C

answer

Circuit 2

None of them


A

B

C

Circuit 3



A

B

C

answer

Circuit 3

A amp C only








A

B

C

Circuit 2



A

B

C

answer

Circuit 2

None of them


A

B

C

Circuit 3



A

B

C

answer

Circuit 3

A amp C only








A

B

C

answer

Circuit 2

None of them


A

B

C

Circuit 3



A

B

C

answer

Circuit 3

A amp C only








A

B

C

Circuit 3



A

B

C

answer

Circuit 3

A amp C only








A

B

C

answer

Circuit 3

A amp C only








book page 84 87 syllabus2.12 2 - wordpress.com •describe how resistance varies with conditions for...

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