Series & parallel circuits

A student investigated how the resistance of a light dependent resistor (LDR) varied with light intensity.

Figure 8 shows the circuit used.

The student connected cells together to make the battery.

How many 1.5 V cells did the student use to make the 6.0 V battery?

Tick () one box.

2 cells 3 cells 4 cells

When the potential difference across the LDR was 3.0 V, the resistance of the LDR was 2000 Ω.

Calculate the current in the LDR.

Use the equation:

The resistor and the LDR were connected in series.

How does the potential difference across the battery compare with the total potential difference across the resistor and LDR?

Tick () one box.

The potential difference across the battery is less.

The potential difference across the battery is the same.

The potential difference across the battery is greater.

The potential difference across the battery was 6.0 V.

The potential difference across the LDR was 3.0 V.

How should the student calculate the potential difference across the resistor?

Tick () one box.

The student plotted a graph to show how the resistance of the LDR varied with light intensity.

Figure 9 shows the results.

What was the resistance of the LDR when the light intensity was 50 arbitrary units?

Which two conclusions can the student make from Figure 9?

Tick () two boxes.

Resistance and light intensity have a non-linear relationship.

Resistance and light intensity have a positive correlation.

Resistance decreases as light intensity increases.

Resistance is directly proportional to light intensity.

Resistance is not affected by light intensity.

LDRs are often used in control circuits.

Which circuit would need an LDR?

Tick () one box.

A circuit to monitor the temperature of an oven.

A circuit to keep the contents of a fridge cold.

A circuit to switch lights on at night.

A student investigated how the resistance of a light dependent resistor (LDR) varies with light intensity.

Figure 4 shows the circuit.

The potential difference across the battery was 6.0 V.

Determine the potential difference across each cell.

When the LDR was in a dark room, the reading on the voltmeter was 3.0 V.

What was the resistance of the LDR?

Give a reason for your answer.

Tick () one box.

1000 Ω 2000 Ω 4000 Ω

The student directed a bright light onto the LDR in the circuit.

Explain why the reading on the voltmeter decreased.

Another student set the circuit up incorrectly.

Figure 5 shows the incorrect circuit.

The student placed the circuit in a dark room and then directed a bright light onto the LDR.

Explain what the reading on the voltmeter would be.

A hairdryer contains a heating element and a motor.

The motor is connected to a fan.

Figure 2 shows part of the electrical circuit inside the hairdryer.

How does the current in the motor compare with the current in the heating element?

Give a reason for your answer.

Tick (✓) one box.

The current is greater in the motor.

The current in both components is the same.

The current is less in the motor.

The potential difference across the motor is 20 V.

What is the potential difference across the heating element?

Give a reason for your answer.

Tick (✓) one box.

20 V 50 V
210 V
230 V

The hairdryer transfers 460 000 J of energy in 250 seconds.

Calculate the power of the hairdryer.

Use the equation:

The current in the hairdryer is 8.0 A.

Calculate the time taken for 1200 C of charge to flow past a point in the hairdryer circuit.

Use the equation:

The hairdryer is connected to the mains electricity supply.

What is the frequency of the UK mains electricity supply?

Tick (✓) one box.

50 Hz 60 Hz
100 Hz
230 Hz

A student investigated electrical circuits.

The student changed the position of the voltmeter.

Figure 14 shows the new circuit.

The student connected the voltmeter across the 15 Ω fixed resistor.

The student used the variable resistor to vary the potential difference across the fixed resistor.

The potential difference across the fixed resistor can only be varied between 6 V and 12 V using the circuit in Figure 14.

Explain why.

Give one way the student could vary the potential difference across the fixed resistor below 6 V.

A student carried out an investigation using an electrical circuit.

Figure 8 shows the circuit used.

The student increased the resistance of the variable resistor.

Describe what happened to the potential difference across resistor R and the current in resistor R.

The student investigated how the current in resistor R varied with the potential difference across resistor R.

To keep the temperature of resistor R constant, the student opened the switch after taking each reading.

Figure 9 shows the results.

Explain what happens to the resistance of resistor R as the potential difference across resistor R increases.

Use information from Figure 9.

After the reading was taken at 4.0 V, the student did not open the switch before taking the reading at 5.0 V.

Explain why the current was lower than expected when the 5.0 V reading was taken.

Figure 8 is repeated below.

The student had more resistors with the same resistance as resistor R.

Describe a method to investigate how the number of resistors in parallel affects the total resistance of the resistors in parallel.