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AS · Practice questions · Potential difference and power

Energy per coulomb.

Six original Cambridge-style questions on V = W/Q and the three power formulas.

Original questions All questions on this page are original work, written in the Cambridge AS & A Level style. They are not from past papers. They test the same concepts and skills the syllabus rewards.
Keep these straight

Three forms of power.

01
Analysis
[2 marks]

Define potential difference and state its unit.

  • Potential difference is the energy transferred per unit charge, V = W/Q ✓
  • The unit is the volt (V), equal to one joule per coulomb ✓
02
Analysis
[2 marks]

A charge of 5.0 C transfers 60 J of energy through a component. Find the potential difference.

  • V = W/Q = 60/5.0 ✓
  • V = 12 V ✓
03
Analysis
[2 marks]

A device operates at 240 V and draws a current of 0.50 A. Find its power.

  • P = VI = 240 × 0.50 ✓
  • P = 120 W ✓
04
Analysis
[3 marks]

A current of 3.0 A flows through an 8.0 Ω resistor. Find the power dissipated and the energy transferred in 2.0 minutes.

  • P = I²R = 3.0² × 8.0 = 72 W ✓
  • Energy = Pt = 72 × 120 = 8640 J ✓
05
Analysis
[2 marks]

A 12 V supply is connected across a 6.0 Ω resistor. Find the power dissipated using P = V²/R.

  • P = V²/R = 12²/6.0 ✓
  • P = 144/6.0 = 24 W ✓
06
Analysis
[3 marks]

An electric heater rated 1150 W runs from a 230 V supply. Find the current it draws and its resistance.

  • I = P/V = 1150/230 = 5.0 A ✓
  • R = V/I = 230/5.0 = 46 Ω ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.