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AS · Practice questions · Potential dividers

Tapping off a voltage.

Six original Cambridge-style questions on the divider equation, design and sensor circuits.

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

Scale by the ratio.

01
Analysis
[2 marks]

State the potential divider equation for the output across the lower resistor R₂.

  • Vₒᵤₜ = V × R₂ / (R₁ + R₂) ✓
  • where V is the supply voltage ✓
02
Analysis
[2 marks]

A 12 V supply is divided by two equal resistors. Find the output across one of them.

  • Equal resistors share the supply equally ✓
  • Vₒᵤₜ = 12 × ½ = 6.0 V ✓
03
Analysis
[3 marks]

A 9.0 V supply is connected across R₁ = 2.0 kΩ and R₂ = 1.0 kΩ in series. Find the output across R₂.

  • Vₒᵤₜ = V R₂/(R₁ + R₂) = 9.0 × 1.0/(2.0 + 1.0) ✓
  • Vₒᵤₜ = 9.0 × 1/3 = 3.0 V ✓
04
Analysis
[3 marks]

A potential divider must give 5.0 V across R₂ = 1.0 kΩ from a 15 V supply. Find the required value of R₁.

  • 5.0 = 15 × 1.0/(R₁ + 1.0), so R₁ + 1.0 = 3.0 ✓
  • R₁ = 2.0 kΩ ✓
05
Analysis
[2 marks]

In a potential divider the output is taken across a thermistor. As the temperature rises, explain what happens to the output voltage.

  • The thermistor resistance falls as it warms ✓
  • so its share of the total resistance falls, and the output voltage across it decreases ✓
06
Analysis
[2 marks]

State the purpose of the null method used with a potentiometer.

  • To compare two potential differences without drawing current at balance ✓
  • the potentiometer is adjusted until the galvanometer reads zero ✓

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.