Current, Potential Difference & Resistance Practice Questions

Name the components A, B and C.

Draw the circuit symbol for a thermistor.

Calculate the time the motor is switched on for, in seconds.

Calculate the charge flow through the motor.

Charge flow = ..................................... $\mathrm{C}$

Write down the reading on ammeter A2.

Explain your answer to part (a).

State what a circuit must contain for electrical charge to flow through it.

Describe how the resistance of a thermistor changes as its temperature increases.

Name the component whose resistance decreases as the light intensity on it increases.

Give one use of a thermistor in a circuit.

Calculate the potential difference across the resistor.

Potential difference = ..................................... $\mathrm{V}$

The resistor is replaced by one with a larger resistance. The potential difference across the new resistor is the same as in part (a).

Explain the effect this has on the current in the resistor.

The two meters in Figure 3 are connected incorrectly. Describe the changes needed so that the circuit can be used to measure the resistance of the resistor.

The student corrected the circuit. The voltmeter then read $6.0\ \mathrm{V}$ and the ammeter read $0.15\ \mathrm{A}$.

Calculate the resistance of the resistor.

Resistance = ..................................... $\Omega$

Plot the data from Table 1 on Figure 4 and draw a line of best fit.

Figure 4

The resistor is an ohmic conductor. Explain how the results show this.

Calculate the resistance of the resistor. Use data from Table 1.

Resistance = ..................................... $\Omega$

Which graph, A or B, was obtained using the filament lamp? Give a reason for your answer.

Explain, in terms of the filament, why the graph for the filament lamp has this shape.

Describe how the current in the diode varies as the potential difference across it is increased from zero in the forward direction.

The student then reversed the connections to the diode and increased the potential difference again. State what the ammeter reading showed and explain why.

In the forward direction, the potential difference across the diode was $0.80\ \mathrm{V}$ when the current was $0.040\ \mathrm{A}$.

Calculate the resistance of the diode at this point.

Resistance = ..................................... $\Omega$

Draw the circuit diagram the student should use. The circuit must allow the student to measure the potential difference across the length of wire and the current in the wire.

Give two variables the student should control in this investigation.

The student opened the switch between each pair of readings. Explain why this improves the investigation.

State what is meant by an electric current.

When the engine is started, there is a current of $120\ \mathrm{A}$ in the starter motor for $3.0$ seconds.

Calculate the charge flow through the starter motor.

Charge flow = ..................................... $\mathrm{C}$

A charge of $9000\ \mathrm{C}$ flows through the car's headlamp circuit in $30$ minutes.

Calculate the current in the headlamp circuit.

Current = ..................................... $\mathrm{A}$

Describe the pattern shown by the data in Table 2.

Explain how the LDR causes the street lamp to switch on when it gets dark.

State how the resistance of the thermistor changes when the temperature in the greenhouse falls.

Explain how the thermistor allows the thermostat to keep the greenhouse at a constant temperature.

Calculate the resistance of the filament lamp at $1.0\ \mathrm{V}$ and at $5.0\ \mathrm{V}$.

Resistance at $1.0\ \mathrm{V}$ = ..................................... $\Omega$

Resistance at $5.0\ \mathrm{V}$ = ..................................... $\Omega$

Explain why the resistance of the lamp is different at these two potential differences.

One of the results is anomalous. Identify the anomalous result and suggest one reason why it may have occurred.

Ignoring the anomalous result, state and justify the relationship between the resistance of the wire and its length.

Explain why the student should keep the temperature of the wire constant, and describe one way of doing this.

Calculate the current in the heating element.

Current = ..................................... $\mathrm{A}$

The heating element is switched on for $10$ minutes. Calculate the charge that flows through the element in this time.

Charge flow = ..................................... $\mathrm{C}$

The element is replaced by a different element, still connected to the $12\ \mathrm{V}$ supply. A charge of $240\ \mathrm{C}$ now flows through the element in $10$ minutes.

Calculate the resistance of the new element.

Resistance = ..................................... $\Omega$

Calculate the resistance of the thermistor at $15\ ^\circ\mathrm{C}$ and at $45\ ^\circ\mathrm{C}$.

Resistance at $15\ ^\circ\mathrm{C}$ = ..................................... $\Omega$

Resistance at $45\ ^\circ\mathrm{C}$ = ..................................... $\Omega$

Use your answers to part (a) to explain what the results show about the thermistor.

Suggest how a thermistor could be used in a circuit that sounds an alarm when a fire starts in a room.