Three concentric conducting spherical surfaces of radii

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Three concentric conducting spherical surfaces of radii R₁, R₂ and R₃ (R₁ < R₂ < R₃) carry charges of –1, –2 and 4 coulombs respectively. The charges on the inner and outer surfaces of the outermost sphere will be respectively (in coulombs)—

1. 0, 4
2. 3, 1
3. – 3, 7
4. – 2, 6

Correct Option: B

The total charge on spheres 1 and 2 taken together is – 1 + (–2) = – 3C. This charge will induced + 3C on inner surface and – 3C on the outer surface of sphere 3. Thus the total charge on the inner surface of sphere 3 is 3C and on the outer surface – 3 + 4 = 1 C.