Electrical energy Revision Notes for AQA GCSE Physics

Electrical energy

What is electrical energy?

Electrical energy is the energy that flows through circuits to make appliances work. Every electrical device in your home transfers energy from one form to another.

You need to understand how energy, charge and potential difference work together.

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The relationship between energy, charge, and potential difference is fundamental to understanding how all electrical devices operate in your home.

Power of a device

Power tells you how quickly a device transfers energy. The power of any electrical device depends on two things:

The potential difference (voltage) across it
The current flowing through it
The energy transferred over a given time

Key fact: A device that transfers more energy in a shorter time has higher power.

Power and stored energy

Different appliances have different power ratings:

A kettle might have a power rating of 2000W (2kW)
A light bulb might have a power rating of 10W

The kettle transfers much more energy to heat each second than the light bulb transfers to light. This is why the kettle heats water quickly but uses more electricity.

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Power ratings help you understand how much electricity different appliances use. Higher power means faster energy transfer but also higher electricity costs.

The energy equation

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Energy transferred = Charge flow × Potential difference

$E = Q × V$

Where:

E = energy transferred in joules (J)
Q = charge flow in coulombs (C)
V = potential difference in volts (V)

Triangle reminder

You can use a triangle to remember this formula:

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    E
   ___
  Q × V

Cover up the quantity you want to find. The position of the other two tells you the formula.

How charge flows

Work is done when charge flows in a circuit.

You can calculate charge using: $Q = I × t$

I = current in amps (A)
t = time in seconds (s)

Circuit connections

When measuring in circuits, remember:

Voltmeters measure potential difference across components (connected in parallel)
Ammeters measure current through components (connected in series)

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Always connect measuring instruments correctly:

Voltmeters in parallel to measure potential difference
Ammeters in series to measure current

Worked example

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Worked Example: Energy Transfer in a Motor

Question: A charge of 25C passes through a motor. The potential difference across the motor is 6V. Calculate the energy transferred.

Answer:

$E = Q × V$
$E = 25C × 6V = 150J$

The motor transfers 150 joules of electrical energy.

Practice calculations

Try these examples:

lightbulbExample

Worked Example 1: Energy Transfer in a Light Bulb

A current of 1.2A flows through a bulb for 2 minutes. The potential difference is 12V. How much energy is transferred?

Steps:

First find charge: $Q = I × t = 1.2A × 120s = 144C$
Then find energy: $E = Q × V = 144C × 12V = 1728J$

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Worked Example 2: Checking Energy Calculations

An LED transfers 144J of energy when 24C of charge flows through it at 6V. Check this makes sense.

$E = Q × V = 24C × 6V = 144J$ ✓

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Key Points to Remember:

$E = Q × V$ is the key equation for electrical energy
Energy is measured in joules (J)
Charge is measured in coulombs (C)
Potential difference is measured in volts (V)
Higher power devices transfer more energy per second
Work is done whenever charge flows through a circuit

Electrical energy (AQA GCSE Physics): Revision Notes