A conducting sphere fo radius 10 cm has an unknown charge. If the electric field 20 cm from the center of the sphere is `1.5xx10^(3) N//C` and points radilly inwards, what is the net charge on the sphere ?

Options

A. `2.35xx10^(-7)C`
B. `5.38xx10^(-11)C`
C. `6.67xx10^(-9)C`
D. None of these

Answer

C

Explanation

Let the value of unknown charge be q.
Electric field at 20 cm away, `E=1.5xx10^(3)NC^(-1)`
From the formula, electric field
`E=(1)/(4piepsilon_(0)).(q)/(r^(2)) rArr 1.5xx106(3)=(9xx10^(9)xxq)/((20xx10^(-2))^(2))`

`q=(1.5xx10^(3)xx20xx20xx10^(-4))/(9xx10^(9))=6.67xx10^(-9)C`
As, the electric field is radially inwards which shown that the nature of unknown charge q is negative.