10.3 B Direct current work and power of current worksheet 3 variant

Power and energy transfers: Worksheet 3

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

We can write this as an equation:

·      power (W) = energy (J) ÷ time (s)

·      1 minute = 60 seconds

·      1 kW = 1000 W

Use this information to answer the following questions:

1.   A 1500 W hairdryer is used for 10 minutes. Calculate:

a)   the time it was on for, in seconds

b)   the total amount of energy transferred by the hairdryer in this time.

2.   An electric oven with a power rating of 2.5 kW is switched on for 45 minutes. Calculate:

a)   the power rating, in watts

b)   the time it was on for, in seconds

c)   the total amount of energy transferred by the oven in this time.

When charge flows in a circuit, electrical work is done. We can calculate the amount of energy transferred by electrical work using the equation:

·      energy transferred (J) = charge flow (C) × potential difference (V)

Use this equation to solve the following:

3.   A charge of 30 C flows through a television that is connected to the mains supply of 230 V. Calculate the total energy transferred.

4.   A device that transfers 600 J of energy has a potential difference of 12 V across it. Calculate the amount of charge that flows through the device.