Download 2 - Science @ St John`s

P2.6a Varying the potential difference
How do the resistances of filament lamps and diodes change when the potential difference is
changed?
Apparatus
power supply
filament lamp
diode
connecting wires
ammeter
voltmeter
resistors
Method
A Set up a circuit as shown in the diagram. Put the resistor in position X.
B Ask your teacher to check your circuit before you switch on. Set your power supply to 2 V. Switch on
and write down the readings on the voltmeter and ammeter.
C Repeat step B with the power supply set to 4 V, 6 V, 8 V, 10 V and 12 V.
D Swap over the connections at the power supply and repeat steps B and C.
You will find that the ammeter and voltmeter give negative readings.
E Replace the resistor with a filament lamp and repeat steps B to D.
F Set up this circuit. The resistor is used to prevent too much current flowing
through the diode being tested and damaging it.
G Ask your teacher to check your circuit before you switch on. Repeat steps
B to D.
Recording your results
1
Draw up a table like this for each component you test.
Power
supply
setting (V)
2
Voltmeter
reading (V)
Ammeter
reading (A)
Resistance
()
2
Calculate the resistance for each set of readings you
have for each component. Use the formula: resistance =
voltage/current.
3
Plot a graph to show how the resistance of each
component changes as the potential difference
changes. Use axes like these:
Considering your results/conclusions
4
How does the resistance of each component change
when the potential difference changes?
© Pearson Education 2011. Edexcel Additional GCSE Science Activity Pack
This document may have been altered from the original.
P2.6b Investigating LDRs and thermistors
Apparatus
power supply
LDR
thermistor
resistor
connecting wires
ammeter
voltmeter
table lamp
2 beakers
hot and cold water
thermometer
light meter
Health and safety
Beware of hot lamp housing.
Method
A Set up circuit X. Use a light meter to record the light level in the room. The
resistor is used to prevent too much current flowing through the LDR. Ask
your teacher to check your circuit before you switch on.
B Switch on and write down the readings on the voltmeter and ammeter.
C Place the table lamp so it is shining directly onto the LDR and switch it on.
Adjust its position so the light meter is showing a higher reading than for
your first measurement. Write down the readings on the ammeter and
voltmeter again.
D Move the lamp closer to the LDR and repeat step C. Keep doing this until
the lamp is right next to the LDR. You should be able to obtain four or five
different readings.
E Set up circuit Y. Switch on and write down the readings on the voltmeter
and ammeter. Use the thermometer to measure the temperature of the air in the room.
F Mix some hot and cold water so that the temperature of the mixture is about 10 °C hotter than the air
in the room.
G Switch off the circuit and carefully put the thermistor into the beaker of hot water. Take care not to spill
the water onto other electrical equipment. Wait for a minute to make sure the thermistor has warmed
up, then take it out of the water and quickly switch the circuit on. Write down the voltmeter and
ammeter readings without delay.
H Repeat steps F and G so you get a set of readings at steadily increasing temperatures.
Recording your results
1
Calculate the resistance for each set of readings you have for each component.
Use the formula: resistance = voltage/current
2
Plot a graph to show how the resistance of each component changes with changing conditions. Use
axes like these:
Considering your results/conclusions
3
How does the resistance of each component change when the conditions change?
© Pearson Education 2011. Edexcel Additional GCSE Science Activity Pack
This document may have been altered from the original.
P2.6c Components and graphs
Cut out the cards and match them up in groups of three to show each component’s name,
symbol and the graph of its characteristics. Label the axes on the graphs using words from the
box. You will need to use some words more than once.
current
light intensity
potential difference
resistance
© Pearson Education 2011. Edexcel Additional GCSE Science Activity Pack
This document may have been altered from the original.
temperature
P2.6d Components and resistances
1
Which component is each phrase describing? Choose your answers from the box. You do not need
all the words in the box.
fixed resistor
a
b
c
d
e
2
variable resistor
filament lamp
diode
light dependent resistor
thermistor
The resistance can be changed by moving a slider or a knob.
The resistance increases when there is a high potential difference.
The resistance gets less when it gets warmer.
It will only conduct electricity in one direction.
The resistance is highest in the dark.
You have a circuit with a variable resistor in it. How will the current in the circuit change if you
increase the resistance?
Use these equations to help you to answer the following questions.
potential difference = current × resistance
current =
potential difference
resistance
resistance =
potential difference
current
3
The potential difference across a resistor is 10 V. There is a 2 A current flowing through it. What is
the resistance of the resistor?
4
A light dependent resistor (LDR) has a resistance of 100 Ω.
a What current will flow through it if the potential difference is 5 V?
b You shine a light on the LDR. What will happen to its resistance?
c What will happen to the current in b if the potential difference stays the same?
5
A thermistor is in a circuit with a potential difference of 12 V. The current is 3 A.
a What is the resistance of the thermistor?
b The circuit is put in a freezer. What will happen to the resistance of the thermistor?
c What will happen to the current in b if the potential difference stays the same?
© Pearson Education 2011. Edexcel Additional GCSE Science Activity Pack
This document may have been altered from the original.
P2.6e Changing resistances
The table shows the results of an experiment to measure the current and potential difference for
a filament lamp. The lamp looked brighter and brighter as the voltage was increased.
Potential
difference (V)
0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
Current (A)
Resistance (Ω)
0.00
0.38
0.64
0.83
0.98
1.10
1.18
1.24
1
Copy the table and complete it to show the resistance of the filament lamp for each potential
difference.
2
What happens to the resistance of the filament lamp as the potential difference increases?
3
a Plot a graph of the potential difference and current. Put potential difference on the horizontal axis.
b How can you tell from the graph that the resistance increases as the potential difference
increases? Use the word 'gradient' in your answer.
Use your graph or the table to help you to work out the answers to these questions.
4
By how much does the current increase if you increase the potential difference:
a from 2 V to 4 V
b from 12 V to 14 V?
5
What do your answers to question 4 tell you about how the resistance of the filament lamp changes?
Explain your answer.
6
Sketch graphs to show how the resistance of the following components change:
a an LDR when the light levels change
b a thermistor when the temperature changes.
Extra challenge
7
Sketch a graph of potential difference (horizontal axis) against resistance for a diode.
© Pearson Education 2011. Edexcel Additional GCSE Science Activity Pack
This document may have been altered from the original.