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CAIE A-Level Physics 10.1.5 Internal Resistance of a Source

Practise explaining and calculating terminal p.d., lost volts, current and internal resistance, and predicting load effects on p.d. and power.

Syllabus
2028–2030
Course
Physics 9702
Level
AS

Exam points

  • explain how internal resistance causes lost volts and makes terminal p.d. differ from e.m.f.
  • calculate current, terminal p.d., lost volts or internal resistance using the source and load relationship
  • interpret how changing load resistance or current affects terminal p.d. and power delivery

10.1.5—The effects of the internal resistance of a source of e.m.f. on the terminal question 1

[Maximum number: 4]

A battery of electromotive force (e.m.f.) E and internal resistance r is connected to a variable resistor of resistance R, as shown in Fig. 6.1.

Fig. 6.1

Fig. 6.1

The current in the circuit is I and the potential difference across the variable resistor is V.

Question (a)

(a)

State an equation relating E, I, r and V.

[ 1 ]

Question (b)

(b)

The resistance R of the variable resistor is varied. The variation with I of V is shown in Fig. 6.2.

Fig. 6.2

Fig. 6.2

Use Fig. 6.2 to:

[ 3 ]

Question (i)

(i)

explain how it may be deduced that the e.m.f. of the battery is 2.8 V

[ 1 ]

Question (ii)

(ii)

calculate the internal resistance r.

r=

Ω\Omega

[ 2 ]
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