10.3 B Direct current work and power of current worksheet 1 variant

Calculating power: Worksheet 1

The power of an appliance is the amount of energy it transfers every second.

We can write this as an equation:

·      power (W) = potential difference (V) × current (A)

Use this information to solve the following:

1.   A kettle draws a current of 12 A from the mains supply, at 230 V.

a)   Calculate the power of the appliance in watts.

b)   Now write this in kilowatts.

2.   An oven has a power rating of 2.3 kW and is connected to the mains. Calculate the current drawn by the oven.

Appliances all provide resistance to the path of the electrical current passing through them. Therefore, it can be shown that the power rating of the appliance depends on both the current flowing through it and the resistance. This is given by the following equation:

·      power = (current)² × resistance

Use this equation and the equation at the top of the page to solve the following:

3.   An electric heater takes a current of 5 A when connected to the 230 V mains electricity supply.

a)   Calculate the power of the heater.

b)   Calculate the resistance of the heater.

4.   A hairdryer has a power rating of 2.3 kW and draws a current of 10 A from the 230 V mains supply. Calculate the resistance of the hairdryer.

5.   An electric drill has a power rating of 1.5 kW. It has a resistance of 10 Ω. Calculate the current passing through the electric drill.