Edexcel A-Level Physics AS 2.4.78 Core Practical 8 E M F and Internal Resistance Questions

Practise Edexcel A-Level Physics Core Practical 8 using electromotive-force internal-resistance circuits, terminal-voltage graphs and gradient methods.

Exam points

draw e.m.f.-internal-resistance circuits with ammeter, voltmeter and variable resistor
determine e.m.f. and internal resistance from best-fit graph intercept and gradient

[Maximum number: 7]

A student carries out an experiment to determine the e.m.f. $\varepsilon$ and internal resistance r of an electrical cell, using a circuit containing an ammeter and a voltmeter.

(a)

Draw a diagram of a circuit that can be used for this experiment.

[ 3 ]

(b)

The student plotted a graph of the terminal potential difference V of the cell against the current I in the cell, as shown. Explain how the e.m.f. $\varepsilon$ and internal resistance r can be determined from this graph.

Figure for Question (b) — Edexcel A-Level Physics AS

[ 4 ]

Conservation of energy gives $\varepsilon=V+Ir$ , or $V=\varepsilon-Ir$ . Comparing with y=mx+c, the y-intercept is the e.m.f. $\varepsilon$ , and the negative of the gradient is the internal resistance r.

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Edexcel A-Level Physics AS 2.4.78 Core Practical 8 E M F and Internal Resistance Questions question 1

Question (a)

Question (b)