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Question
Four cells each of e.m.f. 2V and internal resistance 0.1 Ω are connected in series to an ammeter of negligible resistance, a 1.6 Ω resistor and an unknown resistor R1. The current in the circuit is 2A. Draw a labelled diagram and calculate:
(i) Total resistance of the circuit,
(ii) Total e.m.f.
(iii) The value of R1 and
(iv) The p.d. across R1.
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Solution
(i) The resistance in the circuit
= (1.6 + 4 × 0.1 + R1) Ω
= (2 + R1) Ω
(ii) Total e.m.f. = No. of cell × e.m.f. of each cell = 4 × 2 = 8 V
(iii) Current in main circuit i = `"Total e.m.f."/"Total resistance"`
or 2 = `8/(2 + "R"_1)`
∴ R1 = `4/2 = 2` Ω
(iv) The p.d. across R1 = V = i R1 = 2 × 2 = 4V
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