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55 ideas · 69 connections
Velocity graphs reveal momentum changes Gradients and areas connect motion to data analysis A force–time graph measures impulse Internal resistance separates e.m.f. from terminal voltage Where does a battery’s power go? A straight-line graph reveals a source’s properties Compare a result with evidence, not just an accepted number A spring experiment tests both a model and a gradient Electrical circuits4.3 Analysing1.1.3 Evaluating1.1.4 Kinematics3.1.1 Newton’s laws of motion3.5.1 E.m.f. and potential difference4.2.2 Power in circuits4.2.5 Internal resistance4.3.2 Force–extension graphs
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A straight-line graph reveals a source’s properties

OCR A AS Physics · Two ideas, one explanation

The source equation has the form of a straight line. A graph of terminal voltage against current separates the e.m.f. from the internal resistance.

V = ε − rI

Follow the reasoning

  1. Plot terminal voltage vertically and current horizontally.
  2. Read the voltage intercept as e.m.f.
  3. Take the magnitude of the negative gradient as internal resistance.
Specification outcomes (4)
  • 4.3.2(c)(i) Use and apply E = I(R + r) and E = V + Ir for internal resistance.
  • 4.3.2(c)(ii) Use techniques and procedures to determine the internal resistance of a cell or power supply.
  • 1.1.3(d)(i) Selection and labelling of axes with appropriate scales, quantities and units.
  • 1.1.3(d)(ii) Measurement of gradients and intercepts from experimental results.
Open the official OCR AS specification ↗

H156 v2.0 · May 2026

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