Current, Potential Difference & Resistance Practice Questions

Complete the table to show the relative mass and the relative charge of the missing particles.

particle	relative mass	relative charge
proton	1	+1
neutron	1
electron		−1

State where in the atom the neutrons are found.

The diagram shows one circuit symbol.

Which component does this symbol represent?

Put a cross ( ☒ ) in the box next to your answer.

☐ A diode

☐ B light-emitting diode (LED)

☐ C light-dependent resistor (LDR)

☐ D thermistor

Draw the circuit symbol for a variable resistor.

State what is meant by an electric current.

Name the particles that carry the charge through the copper wires.

The alarm sounds for $3.0$ minutes.

Calculate the charge that flows through the buzzer in this time.

charge = ............................................... C

Determine the reading on ammeter A3.

reading on A3 = ............................................... A

The switch is opened. All three ammeters now read zero.

Explain why.

Calculate the resistance of the resistor.

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

The potential difference across the resistor is increased to $9.0$ V. The resistance of the resistor does not change.

Calculate the new current in the resistor. Give your answer in mA.

current = ............................................... mA

State what is meant by the potential difference across the motor.

When a charge of $450$ C passes through the motor, $5400$ J of energy is transferred.

Calculate the potential difference across the motor.

potential difference = ............................................... V

Draw a circuit diagram of a circuit the student could use to measure the current in the motor and the potential difference across the motor.

The student now adds a variable resistor in series with the motor.

Explain what happens to the current in the motor when the resistance of the variable resistor is increased.

An electric toothbrush is charged using a constant current of $0.35$ A. A charge of $2520$ C flows into the battery during a full charge.

Calculate, in hours, the time taken for the battery to charge fully.

time = ............................................... hours

Use the readings taken at $6.0$ V to calculate the resistance of the wire.

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

Suggest one advantage of taking readings at three different potential differences rather than at only one.

Calculate the charge that flows through the lamp in this time.

charge = ............................................... C

Calculate the energy transferred by the lamp in this time.

energy transferred = ............................................... J

The student writes this conclusion:

'The current in the wire is directly proportional to the potential difference across it.'

Comment on the student's conclusion. Use information from the table in your answer.

Estimate the current in the wire when the potential difference across it is $10.0$ V. Assume the temperature of the wire stays constant.

current = ............................................... A

An electric fence energiser sends a short pulse of charge along the fence wire. During one pulse the potential difference is $5000$ V and $0.60$ J of energy is transferred. The pulse lasts $0.20$ ms.

Calculate the average current during the pulse.

current = ............................................... A

Describe how the student could use this equipment to obtain an accurate value for the resistance of a $50$ cm length of the nichrome wire.

Include a circuit diagram in your answer.