Potentiometer — A/L Physics

What must I remember about Potentiometer?

• Potentiometer Principle: A uniform resistance wire of length L carrying a constant steady current: Potential difference V across any length l is strictly proportional to that length: V ∝ l => V = k l, where k = V/L is Potential Gradient (V/m).
• Null-Deflection Measurement: At the balance point, the test cell emf or terminal voltage is precisely balanced against wire voltage; galvanometer draws ZERO current (Ig = 0); acts as an IDEAL infinite-resistance voltmeter.
• Comparison of EMFs of Two Cells: With driver battery emf E0 > E1, E2: Balance lengths l1 and l2 give E1 / E2 = l1 / l2.
• Measurement of Internal Resistance (r) of Cell: On open circuit: E = k l1; Connected across shunt resistance R: Terminal voltage V = k l2; Internal resistance r = R * [(l1 - l2) / l2].

Test yourself (1 minute)

1. Primary Circuit Mandatory Conditions

   1) Driver battery EMF E0 MUST be greater than test EMF E (E0 > E); 2) Positive terminal of driver cell and positive terminal of test cell MUST be connected to the SAME zero-index terminal (node A).

2. Increasing Potentiometer Sensitivity

   To detect smaller potential differences, make potential gradient k smaller (flatter) by increasing wire length L or adding series rheostat in primary driver circuit.

3. Calibration of Potentiometer

   Determining exact numerical value of potential gradient k using a standard cell of certified emf (e.g., Weston cadmium cell E_std = 1.0186 V): k = E_std / l_std.

Practise Potentiometer questions today

Source: NIE G.C.E. (A/L) Physics Resource Book - Unit 7: Current Electricity

What should I study first?

What comes next?

Next in the syllabus

Where does Potentiometer fit in the syllabus?

Unit 7.8 · Year 2 · Term 1