Calculating Energy Transfers (Edexcel IGCSE Science)

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

$E=0.7\times4\times60$

$E=168J$

Exam Hint '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.