Current, resistance & potential difference

A student investigated how the resistance of a light dependent resistor (LDR) varied with light intensity.

Figure 8 shows the circuit used.

The student connected cells together to make the battery.

How many 1.5 V cells did the student use to make the 6.0 V battery?

Tick () one box.

2 cells 3 cells 4 cells

When the potential difference across the LDR was 3.0 V, the resistance of the LDR was 2000 Ω.

Calculate the current in the LDR.

Use the equation:

The resistor and the LDR were connected in series.

How does the potential difference across the battery compare with the total potential difference across the resistor and LDR?

Tick () one box.

The potential difference across the battery is less.

The potential difference across the battery is the same.

The potential difference across the battery is greater.

The potential difference across the battery was 6.0 V.

The potential difference across the LDR was 3.0 V.

How should the student calculate the potential difference across the resistor?

Tick () one box.

The student plotted a graph to show how the resistance of the LDR varied with light intensity.

Figure 9 shows the results.

What was the resistance of the LDR when the light intensity was 50 arbitrary units?

Which two conclusions can the student make from Figure 9?

Tick () two boxes.

Resistance and light intensity have a non-linear relationship.

Resistance and light intensity have a positive correlation.

Resistance decreases as light intensity increases.

Resistance is directly proportional to light intensity.

Resistance is not affected by light intensity.

LDRs are often used in control circuits.

Which circuit would need an LDR?

Tick () one box.

A circuit to monitor the temperature of an oven.

A circuit to keep the contents of a fridge cold.

A circuit to switch lights on at night.

A student investigated how the resistance of a light dependent resistor (LDR) varies with light intensity.

Figure 4 shows the circuit.

The potential difference across the battery was 6.0 V.

Determine the potential difference across each cell.

When the LDR was in a dark room, the reading on the voltmeter was 3.0 V.

What was the resistance of the LDR?

Give a reason for your answer.

Tick () one box.

1000 Ω 2000 Ω 4000 Ω

The student directed a bright light onto the LDR in the circuit.

Explain why the reading on the voltmeter decreased.

Another student set the circuit up incorrectly.

Figure 5 shows the incorrect circuit.

The student placed the circuit in a dark room and then directed a bright light onto the LDR.

Explain what the reading on the voltmeter would be.

A student investigated how the current in a filament lamp varies with the potential difference across the lamp.

Figure 9 shows the circuit used.

Figure 10 shows the results.

Describe a method the student could have used to obtain the results in Figure 10.

How does an increase in the temperature of a filament lamp affect the resistance of the filament lamp?

Tick () one box.

The resistance of the filament lamp decreases.

The resistance of the filament lamp stays the same.

The resistance of the filament lamp increases.

The results for other components are different from the filament lamp.

Draw one line from each component to the correct graph.

A student investigated how the resistance of a filament lamp varies with the current in the lamp.

Figure 17 shows the circuit used.

Describe a method the student could use to show how the resistance of the filament lamp varies with the current.

When the potential difference across the filament lamp was 12.0 V, the resistance of the lamp was 30 Ω.

Calculate the power output of the lamp when the potential difference across the lamp was 12.0 V.

Use the Physics Equations Sheet.

A student investigated how the current in a filament lamp varies with the potential difference across the filament lamp.

Figure 11 shows the circuit used.

What is component P ?

Tick (✓) one box.

A battery

A variable resistor

An open switch

The student measured different values of potential difference and the corresponding values of current for the filament lamp.

Describe how the student could use the circuit in Figure 11 to make these measurements.

Figure 12 shows the reading on the ammeter at one point in the investigation.

Figure 12

What is the reading on the ammeter?

The student repeated the investigation for two other components.

The student plotted a graph of current against potential difference for each component.

Draw one line from each component to the correct graph.

Component Graph

A student investigated how the resistance of a wire varies with the length of the wire.

Figure 6 shows how the student connected the wire to a circuit.

Which piece of equipment should the student use to measure the length of wire between the crocodile clips?

The student used readings from the circuit to calculate the resistance of the wire at different lengths.

Figure 7 shows the results.

Draw a line of best fit on Figure 7.

A 100 cm length of wire is placed between the crocodile clips.

Predict the resistance of the 100 cm length of wire.

Use Figure 7.

Describe how the results on Figure 7 show that resistance is directly proportional to length.

The student switched the circuit off between readings.

Another student did the same investigation but did not switch the circuit off between readings.

What would happen to the temperature of the wire if the circuit was not switched off between readings?

What would happen to the resistance of the wire if the circuit was not switched off between the readings?

When the student switched the circuit off the ammeter reading was 0.02 A.

What type of error caused the ammeter reading to be 0.02 A?

Tick (✓) one box

A human error

A random error

A zero error

A thermistor is an electrical component.

What is the circuit symbol for a thermistor?

Tick (✓) one box.

A student investigated how the resistance of a thermistor varies with temperature.

Figure 15 shows the results.

Suggest why the student was not able to take measurements at temperatures below 20 °C.

The student used an ammeter and a voltmeter to take measurements to determine the resistance of the thermistor.

Describe a method the student could have used to obtain the results shown in Figure 15.

Figure 15 is repeated below

Use the Physics Equations Sheet to answer Questions 10.4 and 10.5.

Write down the equation which links current (I), potential difference (V) and resistance (R).

The potential difference across the thermistor was 6.0 V.

Determine the current in the thermistor when the temperature of the thermistor was 40 °C.

Use Figure 15.

A thermistor is an electrical component.

What is the circuit symbol for a thermistor?

Tick (✓) one box.

A student investigated how the resistance of a thermistor varies with temperature.

Figure 7 shows the results.

Suggest why the student was not able to take measurements at temperatures below 20 °C.

The student used an ammeter and a voltmeter to take measurements to determine the resistance of the thermistor.

Describe a method the student could have used to obtain the results shown in Figure 7.

Figure 7 is repeated below.

Use the Physics Equations Sheet to answer Questions 03.4 and 03.5.

Write down the equation which links current (I), potential difference (V) and resistance (R).

The potential difference across the thermistor was 6.0 V.

Determine the current in the thermistor when the temperature of the thermistor was 40 °C.

Use Figure 7.

A solar cell generates a potential difference when light shines on its surface. A student investigated how the potential difference varied with the light intensity at the surface of the solar cell.

Figure 13 shows some of the equipment used by the student.

The voltmeter displayed the potential difference generated by the solar cell.

The student varied the light intensity by changing the height of the torch above the solar cell.

Figure 14 shows the results.

Describe a method the student could have used to obtain the results shown in Figure 14.

The circuit symbol for a solar cell is:

Figure 15 shows the solar cell in a circuit with an LED and a resistor.

Figure 16 shows how the current in the LED varies with the potential difference across the LED.

What is the range of potential difference values for which the LED emits light in Figure 16 ?

Range of values = ______________________ to ______________________ V

Use the Physics Equations Sheet to answer questions 09.3 and 09.4.

Which equation links current (I), potential difference (V) and resistance (R)?

Tick (✓) one box.

Determine the resistance of the LED when the potential difference across the LED is 2.7 V.

Use Figure 16.

Describe how the resistance of the LED varies as the p.d. increases from 0 V to 3.7 V.

Use data from Figure 16.

A solar cell generates a potential difference when light shines on its surface. A student investigated how the potential difference varied with the light intensity at the surface of the solar cell.

Figure 3 shows some of the equipment used by the student.

The voltmeter displayed the potential difference generated by the solar cell.

The student varied the light intensity by changing the height of the torch above the solar cell.

Figure 4 shows the results.

Describe a method the student could have used to obtain the results shown in Figure 4.

The circuit symbol for a solar cell is:

Figure 5 shows the solar cell in a circuit with an LED and a resistor.

Figure 6 shows how the current in the LED varies with the potential difference across the LED.

What is the range of potential difference values for which the LED emits light in Figure 6 ?

Range of values = ______________________ to ______________________ V

Use the Physics Equations Sheet to answer questions 02.3 and 02.4.

Which equation links current (I), potential difference (V) and resistance (R)?

Tick (✓) one box.

Determine the resistance of the LED when the potential difference across the LED is 2.7 V.

Use Figure 6.

Describe how the resistance of the LED varies as the p.d. increases from 0 V to 3.7 V.

Use data from Figure 6.

A normal bicycle can be converted into an electric bicycle.

Figure 1 shows a converted bicycle.

Figure 2 shows the circuit diagram for the bicycle.

The circuit symbol for a motor is: M

The potential difference across the motor is 36 V.

The power output of the motor is 252 W.

Calculate the current in the motor.

Use the equation:

The bicycle battery can be recharged using the mains electricity supply.

A battery supplies direct current.

Mains electricity supplies alternating current.

Which graph shows an alternating current?

Tick (✓) one box.

A diode is used to change the alternating current to a direct current.

Which graph shows how the current in a diode varies with potential difference?

Tick (✓) one box.

The mean charging current from the mains is 5.0 A for 7200 seconds.

Calculate the charge flow to the battery.

Use the equation:

charge flow = current × time

Choose the unit from the box.

Calculate the work done in charging the battery when the power input is 1150 W for 7200 seconds.

Use the equation:

work done = power × time

A normal bicycle can be converted into an electric bicycle.

Figure 9 shows a converted bicycle.

Figure 10 shows the circuit diagram for the bicycle.

The circuit symbol for a motor is: M

The switch is used to turn the motor on or off.

Explain how the variable resistor is used to control the speed of the motor.

The battery can be recharged using the mains electricity supply.

The mains supply is alternating current.

Figure 11 shows a simplified version of the circuit that is used to recharge the battery.

Explain why charge only passes in one direction through the circuit.

The mains supply fully recharged the battery in 2 hours.

The mean charging current was 5.0 A.

The resistance of the battery was 0.18 Ω.

Calculate the energy dissipated due to the resistance of the battery in 2 hours.

Use the Physics Equations Sheet.

Two students investigated how the current in filament lamp L varied with the potential difference across the lamp.

Figure 9 shows the circuit used.

What is component P ?

Tick (✓) one box.

Battery

Cell

Fuse

The resistance of the variable resistor is increased.

How does increasing the resistance of the variable resistor affect the reading on the ammeter?

Tick (✓) one box.

The ammeter reading decreases.

The ammeter reading stays the same.

The ammeter reading increases.

Figure 10 shows the results.

Figure 11 shows the line of best fit drawn by each student.

Figure 11

Potential difference in volts
Potential difference in volts

Explain why student B ’s line of best fit is correct.

What type of error will have caused the point at 2 V to be above the line of best fit?

Tick (✓) one box.

A random error

A systematic error

A zero error

When the potential difference across the filament lamp is 1.5 V, the current in the lamp is 0.3 A.

Calculate the resistance of the filament lamp.

Use the equation:

The students investigated how the length of a wire affects the resistance of the wire.

Figure 12 shows the circuit used.

The temperature of the wire was kept constant.

Identify the variables in the investigation.

Tick (✓) one box in each row.

A student carried out an investigation using an electrical circuit.

Figure 8 shows the circuit used.

The student increased the resistance of the variable resistor.

Describe what happened to the potential difference across resistor R and the current in resistor R.

The student investigated how the current in resistor R varied with the potential difference across resistor R.

To keep the temperature of resistor R constant, the student opened the switch after taking each reading.

Figure 9 shows the results.

Explain what happens to the resistance of resistor R as the potential difference across resistor R increases.

Use information from Figure 9.

After the reading was taken at 4.0 V, the student did not open the switch before taking the reading at 5.0 V.

Explain why the current was lower than expected when the 5.0 V reading was taken.

Figure 8 is repeated below.

The student had more resistors with the same resistance as resistor R.

Describe a method to investigate how the number of resistors in parallel affects the total resistance of the resistors in parallel.

An oven is connected to the mains electricity supply using a three-core cable.

Figure 3 shows the three-core cable.

The insulation covering the earth wire has green and yellow stripes.

Give the colours of the insulation covering the live wire and the neutral wire.

A thermistor is used as part of a temperature sensor in the oven.

What is the circuit symbol for a thermistor?

Tick (✓) one box.

Figure 4 shows how the resistance of the thermistor in the oven varies with temperature.

Which statement describes the relationship shown in Figure 4 ?

Tick (✓) one box.

As temperature increases, resistance decreases.

As temperature increases, resistance stays the same.

As temperature increases, resistance increases.

Which temperature range shows the greatest decrease in the resistance of the thermistor?

Tick (✓) one box.

Between 50 and 100 °C

Between 100 and 150 °C

Between 150 and 200 °C

Between 200 and 250 °C

The resistance of the heating element in the oven is 5.0 Ω.

The current in the heating element is 12 A.

Calculate the power output of the heating element.

Use the equation:

power = (current)² × resistance

Calculate the energy transferred by the oven when 8000 C of charge flows through the heating element.

The potential difference across the heating element is 230 V.

Use the equation:

energy transferred = charge flow × potential difference

An LED on the oven is connected to an alternating current supply.

When the supply is switched on, the LED flashes on and off continuously.

Explain why.

A student investigated how the resistance of a piece of wire varied with the length of the wire.

Figure 12 shows an ammeter the student could have used in the investigation.

What is the resolution of the ammeter?

Which quantity must stay the same so the wire behaves as an ohmic conductor?

Tick (✓) one box.

Air pressure

Density of the wire

Temperature of the wire

Write down the equation which links current (I), potential difference (V) and resistance (R).

For one length of wire the potential difference across the wire was 1.68 V.

The current in the wire was 0.70 A.

Calculate the resistance of this length of wire.

Figure 13 shows the circuit used in the investigation.

The student plotted a graph of resistance against length of the wire.

Describe a method the student could use to obtain the data needed to plot the graph.

A student investigated how the resistance of a piece of wire varied with the length of the wire.

Figure 3 shows an ammeter the student could have used in the investigation.

What is the resolution of the ammeter?

Which quantity must stay the same so the wire behaves as an ohmic conductor?

Tick (✓) one box.

Air pressure

Density of the wire

Temperature of the wire

Write down the equation which links current (I), potential difference (V) and resistance (R).

For one length of wire the potential difference across the wire was 1.68 V.

The current in the wire was 0.70 A.

Calculate the resistance of this length of wire.

Figure 4 shows the circuit used in the investigation.

The student plotted a graph of resistance against length of the wire.

Describe a method the student could use to obtain the data needed to plot the graph.

A thermistor is used in an oven as part of a temperature sensor.

Draw the circuit symbol for a thermistor.

Figure 11 shows how the resistance of the thermistor varies with temperature.

Identify the temperature range when the thermistor is most sensitive to temperature change.

Tick (✓) one box.

Between 50 and 100 °C

Between 100 and 150 °C

Between 150 and 200 °C

Between 200 and 250 °C

The potential difference across the thermistor is 15 V.

The current in the thermistor is 0.015 A.

Calculate the energy transferred by the thermistor in 20 minutes.

The power output of the heating element in the oven is 0.72 kW.

The current in the heating element in the oven is 12 A.

Calculate the resistance of the heating element.

Figure 7 shows part of the magnetic field around a bar magnet.

Figure 7

Complete Figure 7 to show the magnetic field around the bar magnet.

You should:

• draw one more magnetic field line

• show the direction of the magnetic field.

A student made an electromagnet from a metal nail and a coil of wire.

Figure 8 shows the electromagnet held in a clamp and connected to a circuit.

When the switch was closed, the electromagnet attracted paper clips.

Which metal should be used for the nail?

Tick (✓) one box.

The student varied the number of turns of wire around the nail.

The student recorded how many paper clips the electromagnet could hold.

Table 1 shows the results.

Predict value X in Table 1.

The student increased the resistance of the variable resistor.

What is the circuit symbol for a variable resistor?

Tick (✓) one box.

Complete the sentences.

Choose answers from the box.

Each answer may be used once, more than once or not at all.

When the resistance of the variable resistor was increased, the current in

the electromagnet.

When the resistance of the variable resistor was increased, the number of paper

clips the electromagnet could hold.

Figure 9 shows an electromagnet being used at a scrapyard.

Give two advantages of using an electromagnet to sort scrap metal compared with using a permanent magnet.

Some street lights automatically switch on when it gets dark.

Figure 13 shows a street light.

The electrical circuit for the street light includes a light-dependent resistor (LDR).

The power supply for the street light uses alternating current.

What is alternating current?

Tick (✓) one box.

Figure 14 shows how the resistance of the LDR varies with light intensity.

Light intensity is measured in lux

How does light intensity affect the resistance of the LDR?

Write down the equation which links current (I), potential difference (V) and resistance (R).

The potential difference across the LDR is 30 V

The current in the LDR is 0.05 A

Calculate the resistance of the LDR.

Determine the light intensity incident on the LDR.

Use your answer to Question 07.4 and Figure 14.

This street light may stay switched on when it is not dark.

What is the most likely cause of this problem?

Tick (✓) one box.

This street light is replaced with one which is more efficient.

What does more efficient mean?

Tick (✓) one box.

A student investigated how the power output of a filament lamp varied with the current in the lamp.

Figure 15 shows part of the circuit the student used.

To calculate power output the student measured the current in the lamp and the potential difference across the lamp.

Complete Figure 15 by adding an ammeter and a voltmeter to make the measurements.

Use the correct circuit symbols.

Which energy store in the battery decreases when the lamp is switched on?

What happens to the energy transferred by the lamp?

Figure 16 shows the results.

Describe how varying the current affects the power output of the filament lamp.

Write down the equation which links current (I), power (P) and resistance (R).

Determine the resistance of the lamp when the current in the lamp is 0.22 A

Some security lights automatically switch on when it gets dark.

Figure 7 shows a security light.

Figure 8 shows part of a circuit that can be used to switch the security light on and off.

The circuit symbol for the LDR in Figure 8 is not correct.

Which is the correct circuit symbol for the LDR?

Tick (✓) one box.

The security light turns on when the potential difference across the LDR is 2.0 V

Determine the resistance of the LDR when the potential difference across the LDR is 2.0 V

Use Figure 8.

A charge of 3.24 C flows through the LDR in 40.0 minutes.

Calculate the current in the LDR.

Sometimes dirt can cover the LDR on the security light.

What effect would dirt on the LDR have on the security light?

Tick (✓) one box.

A student investigated how the resistance of a thermistor varies with temperature.

The student made measurements to determine the resistance of the thermistor at room temperature. He used an ammeter and a voltmeter.

Complete the circuit diagram to show a circuit the student could use.

The student repeated the measurements with the thermistor at different temperatures.

He plotted a graph of resistance against temperature.

Figure 6 shows the graph.

One set of readings was:

• potential difference = 5.60 V

• current = 0.04 A

Determine the temperature of the thermistor.

Explain how the graph shows that the thermistor is most sensitive to changes in temperature between 20 °C and 25 °C