Calculating Energy Transfers (Edexcel IGCSE Physics (Modular))

Revision Note

Author

Katie M

Expertise

Physics

Calculating energy transfers

Work is done when charge flows through a circuit
- Work done is equal to the energy transferred
The amount of energy transferred by electrical work in a component (or appliance) depends upon:
- The current, I
- The potential difference, V
- The amount of time the component is used for, t

When charge flows through a resistor, for example, the energy transferred is what makes the resistor hot
The energy transferred can be calculated using the equation:

$E = P \times t$

Where:
- E = energy transferred in joules (J)
- P = power in watts (W)
- t = time in seconds (s)

P = IV as explained in Electrical power & fuses
- So this equation can also be written as:

$E = I \times V \times t$

Where:
- I = current in amperes (A)
- V = potential difference in volts (V)

When charge flows around a circuit for a given time, the energy supplied by the battery is equal to the energy transferred to all the components in the circuit
You can read more about how energy is transferred in our revision note, Energy Stores & Transfers

Worked Example

Calculate the energy transferred in 1 minute when a current of 0.7 A passes through a potential difference of 4 V.

Answer:

Step 1: Write down the known quantities

Time, t = 1 minute = 60 s
Current, I = 0.7 A
Potential difference, V = 4 V

Step 2: Write down the relevant equation

$E = I \times V \times t$

Step 3: Substitute in the values

$E = 0.7 \times 4 \times 60$

$E = 168 J$

Exam Tip

'Energy transferred' and 'work done' are often used interchangeably in equations, don't panic, they mean the same thing! Always remember that the time t in the above equations must always be converted into seconds.

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