State the equation linking voltage, current and resistance (1)

voltage = current x resistance

Calculate the voltage across the 4.0 resister

1.2 x 4.0 = 4.8V

Show that the voltage across the heater coil is about 7V

12 - 4.8 = 7.2V

what is the formula linking energy transferred, voltage, time, current

energy transferred = voltage x time x current

At first, the temperature of the water increases.

After a while, the temperature reaches a steady value below the boiling point of water

Explain why the temperature reaches a steady value (2)

Rate of energy losses = rate of energy supply (at steady temp)

X - Series

Y - Parallel

Describe the advantages and disadvantages of design X when used as a heater in a car window (3)

- It is a series circuit

- Series circuits have fewer wires and lower resistance

- In series, if one fails, the circuit fails, no independent control

Time - 5 minutes

Voltage - 7.2 V

Current - 1.2 A

Work out the energy transferred (3)

(5 x 60) = 300

300 x 1.2 x 7.2 = 2592

= 2600J

At first, the temperature of water increases

After a while, the temperature reaches a steady value below the boiling point of water.

Explain why the temperature reaches a steady value (2 marks)

- Energy losses occur

- Rate of energy loss = Rate of energy supply (at steady temp)

Advantages and disadvantages of using a series circuit when used as a heater in a car window (3 marks)

- Advantages : Fewer wires, lower resistance

- Disadvantages : One fault causes entire circuit to fail, no independent control

Describe the method a student should use to investigate how the resistance of a wire depends on its length [5 marks]

- Connect the circuit / connect (crocodile) clip to wire

- Read ammeter; Read voltmeter

For known length; measure length with a ruler

- Repeat readings / average

- Take readings for different lengths

- Check meters for zero errors

- Switch off between readings to avoid heating the wire;