Two point charges A = + 3 n C and B = + 1 nC are placed 5 cm apart in the air. The work done to move charge B towards A by 1 cm is

Question

Two point charges A = + 3 n C and B = + 1 nC are placed 5 cm apart in the air. The work done to move charge B towards A by 1 cm is, 2.0 × 10 - 7 J, 2.7 × 10 - 7 J, 12.1 × 10 - 7 J, 1.35 × 10 - 7 J

MARKS App · Accepted Answer

Given, A = + 3 n C = 3 × 10 - 9 C B = + 1 n C = 1 × 10 - 9 C Distance, r 1 = 5 c m = 0.05 m = 5 × 10 - 2 m Work done W = U B - U A = k q 1 q 2 r 2 - k q 1 q 2 r 1 Here, r 2 = r 1 - 1 r 2 = 5 - 1 = 4 c m = 0.04 m = 4 × 10 - 2 m = k q 1 q 2 1 r 2 - 1 r 1 = 9 × 10 9 × 3 × 10 - 9 × 1 × 10 - 9 1 4 × 10 - 2 - 1 5 × 10 - 2 = 27 × 10 - 9 × 1 5 × 4 × 10 - 2 = 27 20 × 10 - 7 = 1.35 × 10 - 7 J

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