PhysicsUK Connections

Connections.EXPLORE · CONNECT · UNDERSTAND YOUR COURSEOCR A · AS Physics Browse topics →
All apps ↗
55 ideas · 69 connections
Charge flow and electrical power Kirchhoff’s second law tracks energy per charge Internal resistance separates e.m.f. from terminal voltage Where does a battery’s power go? Accelerating voltage becomes electron kinetic energy LED voltage links electrical and photon energy A straight-line graph reveals a source’s properties Charge and current4.1 Energy, power and resistance4.2 Analysing1.1.3 Kinetic and potential energies3.3.2 E.m.f. and potential difference4.2.2 Power in circuits4.2.5 Series and parallel circuits4.3.1 Internal resistance4.3.2 Photons4.5.1
100%
PHYSICSUK CONNECTIONS
Physics connection

Internal resistance separates e.m.f. from terminal voltage

OCR A AS Physics · Two ideas, one explanation

A real source transfers some energy internally when current flows. The terminal potential difference is therefore below its e.m.f. when the source supplies current.

V = ε − Ir

Follow the reasoning

  1. Identify the e.m.f. and internal resistance of the source.
  2. Find the current in the complete circuit.
  3. Subtract the internal voltage drop to find terminal voltage.
Specification outcomes (5)
  • 4.2.2(b) Define electromotive force (e.m.f.) of a source such as a cell or power supply.
  • 4.2.2(c) Distinguish between e.m.f. and p.d. in terms of energy transfer.
  • 4.3.2(a) Define source of e.m.f. and internal resistance.
  • 4.3.2(b) Define terminal potential difference and 'lost volts'.
  • 4.3.2(c)(i) Use and apply E = I(R + r) and E = V + Ir for internal resistance.
Open the official OCR AS specification ↗

H156 v2.0 · May 2026

See it in an exam

A curated collection of checked examples. Coverage is growing; this is not a complete past-paper catalogue.

Put the ideas to work

More practice is on its way

No PhysicsUK question linked yet. New eligible questions appear here as the bank grows.