A voltmeter of variable ranges 3 V , 15 V , 150 V is to be designed by connecting resistances R 1 , R 2 , R 3 in series with a galvanometer of resistance G = 20 Ω , as shown in the figure. The galvanometer gives full pass through its coil.

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A voltmeter of variable ranges 3 V , 15 V , 150 V is to be designed by connecting resistances R 1 , R 2 , R 3 in series with a galvanometer of resistance G = 20 Ω , as shown in the figure. The galvanometer gives full pass through its coil. Then, the resistances R 1 , R 2 and R 3 (in kilo ohms) should be, respectively

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Correct answer: B. 2.98 , 12 , 135

R = V I g – R g R 1 = 3 I g – R g = 2980 Ω = 2.98 k Ω R 1 + R 2 = 15 I g – R g = 14980 Ω = 14.98 k Ω R 1 + R 2 + R 3 = 150 I g – R g = 149980 Ω = 149.98 k Ω ⇒ R 1 = 2.98 k Ω R 2 = 14.98 – 2.98 = 12 k Ω R 3 = 149.98 – 14.98 = 135 k Ω

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