E.m.f. and internal resistanceEdexcel International A Level Physics: Mind map

Exam questions on E.m.f. and internal resistance

1. A technician connects a high-resistance voltmeter across the terminals of a new cell with nothing else in the circuit and reads 1.60 V. She then connects a 4.0 Ω resistor across the cell and the voltmeter reading falls to 1.50 V.
   Calculate the internal resistance of the cell.2 marks
2. A cell of e.m.f. 3.0 V and internal resistance 0.50 Ω is connected in series with a lamp of resistance 5.5 Ω.
   Calculate the energy dissipated in the internal resistance of the cell in 60 s.2 marks
3. In Core Practical 8 a student connects a cell, a variable resistor, an ammeter and a high-resistance voltmeter across the terminals of the cell. She records the terminal potential difference V for several different currents I and plots V against I. Her line of best fit has an intercept on the V axis of 1.58 V and a gradient of −0.62 V A⁻¹.
   Explain how the e.m.f. and the internal resistance of the cell are found from the line, and state their values.3 marks