Question : The electric charges are distributed in a small volume. The flux of the elctric field through a spherical surface of radius 10 cm surrounding the total charge is 20 Vm. The flux over a concentric sphere of radius 20 cm will be
a) 20 Vm
b) 25 Vm
c) 40 Vm
d) 200 Vm
Doubt by Dev
Ans : a) is the correct option.
Detailed Solution :
Note Here it is 20 Vm not 20 V/m. Most of the students think that 20 Vm is electric field but actually it is Electric Flux. Vm is the unit of electric flux while V/m is the unit of Electric field.
We know,
As per the Gauss's Theorem,
ΦE = q/ε₀
Clearly, Electric flux does not depend on the size of the gaussian surface whether it is a sphere of 10 cm radius or a sphere of radius 20 cm.
So the electric flux over the concentric sphere of radius 20 cm will be same as over the sphere of radius 10 cm i.e. 20 Vm
Hence, a) would be the correct option.
