Current, Potential Difference & Resistance (AQA GCSE Combined Science: Trilogy: Physics): Exam Questions

Figure 1 shows a graph of current against potential difference for a circuit component

Figure 1

What is the name of the component?

Explain how the resistance of the component changes as the potential difference across it increases.

LED lamps are considerably more energy efficient than the old filament bulbs that can be found in many houses.

What does 'more energy efficient' mean?

It is useful to be able to detect temperature, and then to turn on a heater when it gets cold.

A thermistor is a component that allows us to do this.

Part of a control circuit for doing this is shown in Figure 2.

Figure 2

The temperature decreases.

What happens to the resistance of the thermistor, the current through the thermistor and the potential difference across it?

Resistance ___________________

Potential difference ___________________

Current ___________________

What is the resistance of the thermistor when the potential difference across it is 3 V?

Give a reason for your answer.

Explain your answer.

Calculate the current through the thermistor when the resistance of the thermistor is 5000 Ω.

Give your answer to 2 significant figures.

The diagram in Figure 3 below shows a sensing circuit which is used to control a set of automatic lights.

Figure 3

What quantity is measured by the voltmeter?

Add an ammeter to the diagram which could measure the current through the LDR.

When the potential difference across the LDR is 6.4 V, the current in the circuit is 4.8 mA.

Calculate the resistance of the LDR.

Explain why the potential difference across the thermistor changes as the temperature in the house decreases.

The circuit is left to run for 10 minutes. Calculate the charge that flows in 10 minutes when the current in the circuit is 4.8 mA

A student investigated how current varies with potential difference for two different resistors.

Her results are shown in Figure 4 below.

Figure 4

Complete the circuit diagram for the circuit that the student could have used to obtain the results shown in the figure above.

Resistor 2 has the higher resistance.

Explain how this is shown by the graph above in Figure 4.

Both resistors behave like ohmic conductors for the full range of potential differences used in this investigation.

Explain what an ohmic conductor is.

Use the graph above in Figure 4 to calculate the resistance of both resistor 1 and resistor 2.

Resistor 1 and resistor 2 are placed in series with each other.

Calculate the Total resistance of this combination.

Thermistors can be used as digital thermometers if their resistance is known at a variety of different temperatures.  

The apparatus required to obtain the data necessary to carry out this calibration is shown in Figure 5 below.

Figure 5

In the space below, draw the circuit symbol for a thermistor.

Calculate the resistance of the thermistor at 15℃, using the data from Figure 5. 

Complete the sketch graph in Figure 6 below to show how the resistance of a thermistor changes between the temperatures of 15 ℃ and 100 ℃.

Figure 6

Give an example of a device that could include a thermistor

Ammeters, which are used in circuits have very low resistances.

Why is it important that ammeters have a very low resistance?

A student plans to change the experiment in Figure 6 to investigate how the resistance of an LDR changes with the intensity of light shone on it.

Once change the student makes is to replace the thermistor with an LDR. 

Suggest two further changes the student should make to the apparatus.

Some students are investigating the I-V characteristics of a fixed resistor.

The students are given the following equipment:

• An ammeter

• A voltmeter

• A variable resistor

• Fixed resistors of 100 Ω, 200 Ω, 400  and 500 Ω

• A power pack

• Wires

Draw a circuit using the equipment from the list that would enable the students to gather valid data.

Describe a method that would allow the students to obtain valid results.

The students plotted their data and produced the graph shown in Figure 1.

Figure 1

Write down an expression for the gradient of the graph in terms of resistance.

Use the graph to determine the resistance of the fixed resistor used by the students.

   Resistance = .................................... Ω

A student is investigating the I-V characteristic of a filament bulb. Figure 1 shows the circuit they set up to conduct the investigation.

Figure 1

The circuit shown in Figure 1 will not provide valid results.

Describe the errors the student has made and state how to rectify them.

The student's readings of current at all potential differences were significantly different to those recorded by another student in her class.

Suggest two possible reasons why.

The student plotted the graph shown in Figure 2 from her data.

Figure 2

Explain how the shape of the graph shows that the filament bulb is a non-ohmic conductor.  

Use the graph shown in Figure 2 to calculate the resistance of the filament lamp when the potential difference is 3 V.

Give your answer to an appropriate number of significant figures.

  Resistance of filament lamp = .................................... Ω

Draw the circuit symbol for a light-dependent resistor (LDR).

A student is designing an experiment to investigate the resistance of light dependent resistors.

This is the method the student has proposed.

1. Set up a circuit with a cell, an analogue ammeter, and an LDR in series, with an analogue voltmeter in parallel across the LDR

2. In a dark room, place a lamp 100 cm away from the LDR and turn it on

3. Measure the readings of current and potential difference

4. Move the lamp to 80 cm away and measure the current and potential difference

5. Repeat at 60 cm, 40 cm, 20 cm, and 0 cm

Suggest two improvements that the student could make and explain how the suggestions would improve the data collected.

Sketch the shape you would expect an IV graph to be for LDR.

Explain how the shape of the graph shows that the LDR is a non-ohmic conductor.

Describe the difference between conventional current and electron flow.

Figure 1 shows the variation in current with potential difference for two components, X and Y.

Figure 1

X and Y are two variants of the same component.

Name the component.

State which component in Figure 1 has the greatest resistance. Explain your answer.

Figure 1 shows an electric car being charged at a charging station.

Figure 1

As the car is being charged, there is a direct potential difference applied across the battery of the car.

Describe what is meant by the term 'direct potential difference'.

The battery of the electric car can store 2.16 ×10⁸ J of energy.

The power output of the charging station is 6.9 kW.

The battery indicator of the car show it to be at 21% when the car is plugged in.

Determine how long it will take to fully charge the car battery.

   Time required to fully charge = .................................... s

Figure 2 shows a simplified diagram of the circuit connecting the battery to the motor of the car.

Figure 2

A current of 13 A flows through the circuit.

There are 167 lithium ion cells, each with a potential difference of 3.2 V, are connected in series to form the battery pack. 

Calculate the resistance of the motor.

   Resistance = .................................... Ω

A charging station can provide a current of 50 A.

Charging an electric vehicle with a three-point plug from a residential mains supply provides 10 A of current.

Both methods use a potential difference of 230 V.

How does the time taken to charge the battery with the high speed charging station compare with the time taken using the mains supply?

Tick (✓) one box.   

Figure 1 shows two torches. Torch A uses a filament lamp. Torch B uses an LED.

Figure 1

Both torches contain a switch and three cells.

Write A in the box that shows the correct diagram for Torch A.

Write B in the box that shows the correct diagram for Torch B. 

The current flowing through Torch A is 45 mA.

The charge flow through the battery is 740 C.

Calculate how long the torch will work for before the cells need replacing.

Give your answer to the nearest minute.

   Time = .................................... minutes

The total power input for both torches is 0.22 W.

The useful power output of the LED is 0.17 W.

The ratio of efficiency of Torch B to Torch A is 3:1.

Calculate the useful power output of Torch A.

   Useful power output of Torch A = .................................... W