Electrical power (AQA GCSE Physics): Revision Notes
Electrical power
What is electrical power?
Electrical power shows how much electrical energy moves to different energy types every second. Think of it as the speed at which energy gets transferred from electricity to other forms like heat, light or movement.
Power is measured in watts (W). One watt means one joule of energy is transferred every second.
How to calculate power
There are three main equations you can use to work out power. Which one you choose depends on what information you already know.
Equation 1: Using current and voltage
- P = power in watts (W)
- I = current in amperes (A)
- V = potential difference in volts (V)
Use this when you know the current flowing through a device and the voltage across it.
Worked Example: Calculating Power from Current and Voltage
An electric oven uses 30A of current at 230V
Power = 30A × 230V = 6900W (or 6900 watts)
Equation 2: Using current and resistance
- P = power in watts (W)
- I² = current squared in amperes (A)
- R = resistance in ohms (Ω)
Use this when you know the current and the resistance of the device.
Worked Example: Calculating Power from Current and Resistance
A current of 4A flows through a 55Ω wire
Power = (4A)² × 55Ω = 16 × 55 = 880W
Equation 3: Using energy and time
- P = power in watts (W)
- E = energy transferred in joules (J)
- t = time taken in seconds (s)
Use this when you know how much energy was transferred over a certain time period.
Worked Example: Calculating Power from Energy and Time
A microwave transfers 300000J of energy in 35 seconds
Power = 300000J ÷ 35s = 8571W (or about 8571 watts)
Important facts to remember
Understanding these key concepts will help you work with electrical power effectively:
Key Points to Remember:
- Power = energy per second - it tells you the rate of energy transfer
- 1 watt = 1 joule per second
- You can rearrange these equations to find current, voltage, resistance, energy or time
- Higher power means more energy is being transferred each second
Remember!
- Electrical power is the rate at which electrical energy transfers to other energy types
- Three key equations: , , and
- Units matter: Power in watts (W), current in amperes (A), voltage in volts (V)
- Choose the right equation based on what values you know
- Power tells you how much energy transfers every second