`4 xx 10^(10)` electrons are removed from a neutral metal sphere of diameter 20 cm placed in air. The magnitude of the electric field (in `N C^(-1)`) at a distance of 20 cm from its centre is

Options

A. Zero
B. 5760
C. 640
D. 1440

Answer

D

Explanation

Number of electrons removed =`4 xx 10^(10)`
`"Charge on this sphere" = 4 xx 10^(10) xx 1.6 xx 10^(-19)C = 6.4 x 10^(-9)C = 6.4 nC`
Diameter of sphere, D = 20 cm = 0.2 m
Distance from the centre, d = 20 cm = 0.2 m

`"Electric field at point" P, E = (q)/(4piepsilon_(0)d^(2))`
`= ((9 xx 10^(9) xx 6.4 xx 10^(-9))/((0.2)^(2)))NC^(-1)= 1440NC^(-1)`