EMF, Internal Resistance & Cells — A/L Physics

How do I practise EMF, Internal Resistance & Cells?

1 question with a worked solution

1. A cell of electromotive force (EMF) E = 6.0 V and internal resistance r = 1.0 Ω is connected across an external resistor R. According to the Maximum Power Transfer Theorem, what is the maximum power that can be delivered to the external resistor?
   1. A) 36.0 W
   2. B) 4.5 W
   3. C) 9.0 W
   4. D) 18.0 W
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   Correct answer: C) 9.0 W

   By the Maximum Power Transfer Theorem, power delivered to external load R is maximized when R = r = 1.0 Ω. At this condition, circuit current is I = E / (R + r) = 6.0 V / (1.0 + 1.0) Ω = 3.0 A. Maximum power delivered is P_max = I² R = (3.0 A)² × 1.0 Ω = 9.0 W (or P_max = E² / (4r) = 36 / 4 = 9.0 W).

   Show worked solution

   Step 1: Maximum power condition: R = r = 1.0 Ω. Step 2: P_max = E² / (4r) = (6.0)² / (4 × 1.0) = 36 / 4 = 9.0 W. Answer: 9.0 W.
   Modelled on: the A/L Physics examination pattern

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Where does EMF, Internal Resistance & Cells fit in the syllabus?

Unit 7.3 · Year 2 · Term 1