E.m.f. and internal resistanceEdexcel International A Level Physics: Flashcards
What these 13 flashcards ask
- Define electromotive force (e.m.f.).
- What is internal resistance?
- What is terminal potential difference?
- Give the equation linking e.m.f., terminal pd and internal resistance.
- When does terminal pd equal e.m.f.?
- What are 'lost volts'?
- Write the e.m.f. equation for a circuit with external resistance R.
- What is the short circuit current of a cell?
- Why does terminal pd fall as the current increases?
- In Core Practical 8, what is plotted and what do the intercept and gradient give?
- Why switch off between readings in Core Practical 8?
- Where is the voltmeter connected in Core Practical 8?
- What is the power wasted inside a cell?
Exam questions on E.m.f. and internal resistance
- 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
- 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
- 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
Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).