Current, Potential Difference & Resistance (AQA GCSE Physics)

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

Figure 1

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

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.

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

Her results are shown in Figure 4 below.

Figure 4

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.

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

Figure 6

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.

• • 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.

Figure 1

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

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.

Figure 2

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

Give your answer to an appropriate number of significant figures.

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.

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.

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.

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.

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.

The mains supply is 5 times faster
The charging station takes 1⁄5 of the time
The mains supply is slower by a factor of 4
The charging station is faster by a factor of 0.5

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.

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.