Energy Transferred Calculator (E = QV)

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Find energy transferred, charge flow or potential difference using E = Q × V. Enter kilojoules or millicoulombs if the question uses them.

Quick answer

Energy transferred = charge flow × potential difference. Use coulombs and volts to get joules. For example, 20 C through a 12 V lamp transfers 20 × 12 = 240 J. If you are given current and time, find Q = It first.

By Mehmood Kakar · Updated

E = Q × V
Find:

How to calculate energy transferred

Potential difference tells you how much energy each coulomb of charge transfers. One volt is one joule per coulomb. So the total energy transferred is:

energy transferred = charge flow × potential difference

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

If 20 C of charge flows through a 12 V lamp, the energy transferred is 20 × 12 = 240 J.

Exam questions often give current and time instead of charge. Work out the charge first with Q = It, then use E = QV. If you have power and time instead, use E = P × t from the power calculator.

Common mistakes that cost marks

  1. Using current instead of charge. E = QV needs charge in coulombs. If you have current, multiply by time in seconds first.
  2. Leaving time in minutes when working out the charge. 1 minute is 60 s.
  3. Not converting kJ. 4.6 kJ is 4600 J.
  4. Mixing up E = QV and E = Pt. Both give energy in joules. Choose the one that matches the quantities you are given.

Practice questions

Try each one on paper first, then reveal the worked answer.

Q120 C of charge flows through a lamp with a potential difference of 12 V. Calculate the energy transferred.[2 marks]
  1. E = Q × V
  2. E = 20 × 12
  3. E = 240 J
Q2A toaster on the 230 V mains transfers 4600 J of energy. Calculate the charge that flows.[2 marks]
  1. Rearrange: Q = E ÷ V
  2. Q = 4600 ÷ 230
  3. Q = 20 C
Q3A current of 0.50 A flows through a 9.0 V motor for 60 s. Calculate the energy transferred.[4 marks]
  1. Step 1: Q = I × t = 0.50 × 60 = 30 C
  2. Step 2: E = Q × V
  3. E = 30 × 9.0
  4. E = 270 J

Frequently asked questions

What is the equation for energy transferred in a circuit?

Energy transferred = charge flow × potential difference (E = QV). Energy is in joules (J), charge in coulombs (C) and potential difference in volts (V).

What does a potential difference of 1 volt mean?

One joule of energy is transferred for every coulomb of charge that flows. So 1 V = 1 J/C.

What if the question gives current and time?

Find the charge first with Q = It, using time in seconds. Then use E = QV.

What is the difference between E = QV and E = Pt?

Both give energy in joules. Use E = QV when you know charge and potential difference, and E = Pt when you know power and time.