Current, Potential Difference & Resistance (Edexcel GCSE Physics)

A resistor is connected to a power supply.

The potential difference across the resistor is 6.0 V.

i) Which of these corresponds to a potential difference of 6.0 V?

☐ A 6.0 joules per ohm

☐ B 6.0 amps per coulomb

☐ C 6.0 joules per coulomb

☐ D 6.0 amps per ohm

[1]

ii) The resistor remains connected for a period of time.

The current in the resistor is 200 mA.

A total charge of 42 C flows through the resistor.

Calculate, in minutes, the time taken for this amount of charge to flow through the resistor.

time = .......................................... minutes[3]

iii) Calculate the total energy transferred by the 6.0V power supply when a charge of 42 C flows through the resistor.

energy = ............................................... J[2]

The resistor becomes warm while there is a current in it.

Explain why the resistor becomes warm.

Figure 16 shows a cardboard tube with a wire coming out from each end.

Figure 16

There are two 10 ohm resistors inside the cardboard tube.

A potential difference of 6.0 V is connected between P and Q.

There is a current of 1.2 A in the wires.

Deduce how the resistors have been arranged inside the cardboard tube.

Which of these symbols is used to represent a thermistor in an electrical circuit?

A student investigates how the current in a lamp changes with the potential difference across the lamp.

The student uses the results to calculate the resistance of the lamp.

The results are shown in the table in Figure 17.

i) One value of resistance is missing from the table in Figure 17.

Calculate the value of resistance that is missing from the table.

[3]

ii) The student writes this conclusion:

‘The resistance of the lamp is directly proportional to the potential difference.’

Comment on the student’s conclusion. Use information from Figure 17 in your answer.

[3]

iii) The student used a power supply that had fixed output voltage settings.

Each of these outputs was a whole number of volts.

Describe how the student could add a component to the circuit that would provide a continuously variable voltage across the lamp.

[2]

Figure 18 shows a battery connected to a filament lamp.

Figure 18

Explain, in terms of the movement of charged particles, how energy is transferred from the battery, through the lamp, to the surroundings.

Figure 17 shows two different types of the same circuit component.

Figure 17

What is the name of this circuit component?

Which row in the table describes the way that ammeters and voltmeters should be connected with a component in a circuit?

Figure 18 shows the results from an experiment where the potential difference (voltage) across a filament lamp was varied.

The current and voltage were measured.

Figure 18

i) Describe the relationship between the current and the voltage as shown in the graph in Figure 18.

[2]

ii) Use the values of the voltage and current at point P and at point Q on the graph in Figure 18 to complete the table in Figure 19.

   Figure 19

iii) Calculate the resistance of the filament lamp when the voltage is 4.5 V and the current is 51 mA.

Use the equation

resistance = ............................................ Ω[2]

iv) Explain why the resistance of the filament lamp changes as the voltage across it increases.

[3]

Which of the following is not true about current?

Figure 1 shows a circuit constructed by a student.

Figure 1

Determine the readings on ammeters A₂ and A₃.

A₂ = .................................... A 

A₃ = .................................... A

Figure 2 shows another circuit the student built.

Figure 2

Determine the reading on the ammeter and voltmeter.

ammeter = .................................... A 

voltmeter = .................................... V

Figure 3 shows another circuit constructed by the student.

Figure 3

Determine the resistance of resistor Z.

   resistance = .................................... Ω

A student investigates resistors connected in series in an electrical circuit. The student has

• a 3.0V battery

• a 22 Ω resistor

• a resistor marked X.

The student does not know the value of the resistor marked X.

The student decides to measure the potential difference (voltage) across resistor X.

Figure 15 shows the circuit that the student connected.

Figure 15

The circuit is connected incorrectly.

Describe how the student should correct the mistake.

The student corrects the mistake.

The voltage across resistor X is 2.1 V.

The circuit is connected to a 3 V battery.

(i) State the value of the voltage across the 22 Ω resistor.

voltage across 22 Ω resistor = ...................................... V[1]

ii) The current in resistor X is 0.041 A.

The voltage across resistor X is 2.1 V.

Show that the resistance of resistor X must be about 50 ohms.

Use the equation

V = I × R

[2]

iii) Calculate the power in resistor X when the voltage across X is 2.1 V and the current in resistor X is 0.041 A.

power = .............................................................. W[2]

iv) Calculate the overall resistance of the 22 ohm resistor and resistor X.

overall resistance = ................................................ Ω[2]

v) The current in the circuit is 0.041 A.

The voltage across the battery is 3.0 V.

Calculate the energy transferred in 2 minutes.

Use the equation

E = I × V × t

energy = .................................................... J[2]

Figure 19 shows two electrical devices for heating water.

Figure 19

i) The current in the element of the immersion heater is 14 A.

The power of the immersion heater is 130 W.

Calculate the resistance of the immersion heater.

Give your answer to two significant figures.

resistance of immersion heater = .................................... Ω[3]

ii) The current in the heating element of the kettle is 8.3 A.

State two differences between the movement of charge in the heating element of the kettle and the movement of charge in the immersion heater.

[2]

Figure 20 shows the three-pin plug used to connect the kettle to the mains.

Figure 20

A fault occurs in the kettle causing the live wire to touch the metal case of the kettle.

Explain how the safety features of the plug operate when this fault occurs.

A light-emitting diode (LED) is a diode that emits light when there is a current in it. 

Draw a circuit diagram showing an LED, connected so that it is lit, in series with a battery and a fixed resistor.

The voltage across the LED when lit is 3.1 V and the current in the LED is 0.030 A.

i) Add to the diagram in (a) to show how these readings were obtained.

[2]

ii) Calculate the value of the resistance of the LED when lit.

[2]

iii) Explain the effect of adding connected an identical LED in series with the first LED.

[2]

The diagram shows a power supply with a voltage of 12 V connected in series with a lamp and a heater.

The voltage across the lamp is 3.2 V and the current in the lamp is 1.5 A.

i) Calculate the resistance of the heater.

[3]

ii) Calculate the power of the heater.

[2]