Calculating Electric Energy (Edexcel GCSE Physics)
Revision Note
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Calculating Electric Energy
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 × t
Where:
E = energy transferred in joules (J)
P = power in watts (W)
t = time in seconds (s)
Since P = IV, this equation can also be written as:
E = I × V × 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
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 × V × t
Step 3: Substitute in the values
E = 0.7 × 4 × 60 = 168 J
Examiner Tips and Tricks
'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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