Figure shows two concentric spherical shells having radii 1 m and 2 m respectively. Outer spherical surface has charge − 3.2 × 1 0 − 15 Coulomb. If inner surface is now earthed by closing the switch t

Question

Figure shows two concentric spherical shells having radii 1 m and 2 m respectively. Outer spherical surface has charge − 3.2 × 1 0 − 15 Coulomb. If inner surface is now earthed by closing the switch then x × 1 0 + y number of electron move towards earth, then ( x + y ) will be ( x , y ∈ I , 0 ≤ x , y ≤ 9 ) .

TestHub · Accepted Answer

Earthing the inner shell leaves charge Q on it such that its potential is zero: $\frac{k ( - 3.2 \times 1 0 ^{- 15} )}{2} + \frac{k Q}{1} = 0$ , giving $Q = 1.6 \times 1 0^{- 15}$ C.

Electrons flowing to earth: $n = \frac{Q}{e} = \frac{1.6 \times 1 0 ^{- 15}}{1.6 \times 1 0 ^{- 19}} = 1 \times 1 0^{4}$ , so x = 1, y = 4 and x + y = 5.

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