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55 ideas · 69 connections
Kirchhoff’s first law conserves charge Kirchhoff’s second law tracks energy per charge Build a resistor network from Ohm’s law A potential divider uses shared current Changing resistance makes a voltage sensor Read circuit connections, not the drawing’s shape Electrical circuits4.3 Charge4.1.1 Circuit symbols4.2.1 E.m.f. and potential difference4.2.2 Resistance4.2.3 Series and parallel circuits4.3.1 Potential dividers4.3.3
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A potential divider uses shared current

OCR A AS Physics · Two ideas, one explanation

Two series resistors carry the same current, so their potential differences are proportional to their resistances. This gives the potential-divider equation.

Vout = Vin R₂/(R₁ + R₂)

Follow the reasoning

  1. Identify the resistor across which output is measured.
  2. Find its fraction of the total series resistance.
  3. Multiply that fraction by the input voltage.
Specification outcomes (4)
  • 4.3.1(c) Calculate total resistance of resistors in series using R = R₁ + R₂ + …
  • 4.3.1(e) Analyse circuits with components including both series and parallel arrangements.
  • 4.3.3(a) Describe potential divider circuits with fixed components and potentiometers.
  • 4.3.3(c)(i) Use potential divider equations Vout = (R₂ / (R₁ + R₂)) × Vin and V₁ / V₂ = R₁ / R₂.
Open the official OCR AS specification ↗

H156 v2.0 · May 2026

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