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Home · IGCSE 0625 · Electricity and magnetism · EMF and p.d. · Practice
Core · Practice questions · EMF and p.d.

Energy per coulomb.

Six original Cambridge-style questions on e.m.f. and potential difference: defining both as energy per charge, the unit and the voltmeter, and using the e.m.f. as the sum of the p.d.s.

Original questions All questions on this page are original work, written in the Cambridge IGCSE style. They are not from past papers. They test the same concepts and skills the syllabus rewards.
The ideas that earn the marks

Push in, drops out, energy balances.

01
Recall
[2 marks]

State what is meant by the potential difference across a component, and name the unit in which it is measured.

  • The energy transferred from each unit of charge (each coulomb) as it passes through the component. ✓
  • It is measured in volts (V). ✓
02
Recall
[2 marks]

A student wants to measure the p.d. across a lamp.

(a) Name the instrument used.
(b) State how it must be connected.

(a) A voltmeter. ✓

(b) In parallel, connected across the lamp. ✓

03
Calculation
[2 marks]

A cell of e.m.f. 9.0 V is connected to two lamps in series. The p.d. across the first lamp is 4.0 V. Calculate the p.d. across the second lamp.

e.m.f. = V1 + V2, so V2 = 9.0 − 4.0

V2 = 5.0 V

04
Recall
[2 marks]

Explain the difference between the e.m.f. of a cell and the p.d. across a component, in terms of energy and charge.

  • The e.m.f. is the energy the cell gives to each coulomb of charge. ✓
  • The p.d. is the energy each coulomb gives up as it passes through that component. ✓
05
Calculation
[3 marks]

Three components are connected in series with a battery. The p.d.s across them are 2.0 V, 3.5 V and 1.5 V. Calculate the e.m.f. of the battery, and state the principle you have used.

e.m.f. = 2.0 + 3.5 + 1.5

e.m.f. = 7.0 V

conservation of energy: the e.m.f. equals the sum of the p.d.s

06
Analysis
[3 marks]

A student connects a voltmeter in series with a lamp, expecting it to read the p.d. across the lamp. Explain why this is wrong, and describe the correct connection. State, in energy terms, what the reading represents when done correctly.

  • A voltmeter must be connected in parallel, across the lamp, not in series. ✓
  • Connected in series it would not measure the p.d. across the lamp (and would block the current). ✓
  • Read correctly, it shows the energy transferred from each coulomb passing through the lamp. ✓

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.