Potential dividers
Cambridge A-Level Physics (9702) · Unit 10: D.C. circuits · 7 flashcards
Potential dividers is topic 10.3 in the Cambridge A-Level Physics (9702) syllabus , positioned in Unit 10 — D.C. circuits , alongside Practical circuits. In one line: A potential divider circuit divides a voltage source into smaller output voltages. The output voltage across a resistor in the series is proportional to its resistance relative to the total resistance in the circuit. V_out = V_in * (R_out / R_total).
Marked as AS Level: examined at AS Level in Paper 1 (Multiple Choice), Paper 2 (AS Structured Questions) and Paper 3 (Advanced Practical Skills). The same content may also be assumed in Paper 4 (A Level Structured Questions).
The deck below contains 7 flashcards — 2 definitions, 3 key concepts and 2 calculations — covering the precise wording mark schemes reward. Use the 2 definition cards to lock down command-word answers (define, state), then move on to the concept and calculation cards to handle explain, describe, calculate and compare questions.
Principle of a potential divider circuit
A potential divider circuit divides a voltage source into smaller output voltages. The output voltage across a resistor in the series is proportional to its resistance relative to the total resistance in the circuit. V_out = V_in * (R_out / R_total)
What the Cambridge 9702 syllabus says
2025-2027 syllabus, in our words · AS LevelWhat the syllabus expects you to be able to do in this topic, in plain English. For the exact wording, see the official syllabus (PDF).
- Understand how a potential divider circuit works.
- Recall the principle of a potentiometer used to compare potential differences, and apply it.
- Understand how a galvanometer is used in null methods.
- Explain how a thermistor or a light-dependent resistor in a potential divider gives a p.d. that varies with temperature (thermistor) or with light intensity (LDR).
Cambridge syllabus keywords to use in your answers
These are the official Cambridge 9702 terms tagged to this section. Mark schemes credit responses that use the exact term — weave them into your answers verbatim rather than paraphrasing.
Tips to avoid common mistakes in Potential dividers
- › Remember that at the balance point, no current flows through the cell being measured, so there are no 'lost volts' across its internal resistance.
State the principle of a potential divider circuit.
A potential divider circuit divides a voltage source into smaller output voltages. The output voltage across a resistor in the series is proportional to its resistance relative to the total resistance in the circuit. V_out = V_in * (R_out / R_total)
Explain how a potentiometer can be used to compare potential differences.
A potentiometer balances an unknown potential difference against a known variable potential difference. When the galvanometer shows zero current (null method), the unknown potential difference is equal to the known potential difference at that position on the potentiometer.
What is the purpose of a galvanometer in null methods?
A galvanometer in a null method acts as a sensitive current detector. It indicates when the potential difference across two points is zero, allowing for precise measurements.
How does a thermistor affect the output voltage of a potential divider as temperature increases?
Typically, thermistors have a negative temperature coefficient (NTC). As temperature increases, the resistance of the thermistor decreases. This changes the voltage division, typically causing the output voltage across the thermistor to decrease (if the thermistor is in the bottom half of the divider).
How does a light-dependent resistor (LDR) affect the output voltage of a potential divider as light intensity increases?
As light intensity increases, the resistance of an LDR decreases. This changes the voltage division, typically causing the output voltage across the LDR to decrease (if the LDR is in the bottom half of the divider).
In a potential divider with two resistors R1 and R2 in series with a voltage source V, what is the formula for the voltage across R2 (V_R2)?
V_R2 = V * (R2 / (R1 + R2)), where V is the total voltage, R1 and R2 are the resistances of the resistors.
A potential divider consists of a 1000Ω resistor and a thermistor in series with a 5V supply. At 25°C, the thermistor's resistance is 500Ω. Calculate the voltage across the thermistor.
V_thermistor = 5V * (500Ω / (1000Ω + 500Ω)) = 5V * (500/1500) = 1.67V
Review the material
Read full revision notes on Potential dividers — definitions, equations, common mistakes, and exam tips.
Read NotesMore topics in Unit 10 — D.C. circuits
Potential dividers sits alongside these A-Level Physics decks in the same syllabus unit. Each uses the same spaced-repetition system, so progress in one informs the next.
Key terms covered in this Potential dividers deck
Every term below is defined in the flashcards above. Use the list as a quick recall test before your exam — if you can't define one of these in your own words, flip back to that card.
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