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The masses of three copper wires are in the ratio 2 : 3 : 5 and their lengths are in the ratio 5 : 3 : 2 . Then, the ratio of their electrical resistances is

Options

  1. A1 : 9 : 15
  2. B2 : 3 : 5
  3. C5 : 3 : 2
  4. D125 : 30 : 8

Correct answer

D. 125 : 30 : 8

Step-by-step solution

As we know that R = ρ l A . So, R 1 : R 2 : R 3 = l 1 A 1 : l 2 A 2 : l 3 A 3 = l 1 2 V 1 : l 2 2 V 2 : l 3 2 V 3 = l 1 2 m 1 d : l 2 2 m 2 d : l 3 2 m 3 d = l 1 2 m 1 : l 2 2 m 2 : l 3 2 m 3 = 5 2 2 : 3 2 3 : 2 2 5 = 25 2 : 3 : 4 5 = 125 : 30 : 8

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