Question

Electric charges are distributed in a small volume. The flux of the electric field through a spherical surface of radius $10$ cm surrounding the total charge is $25$ V-m. The flux over concentric sphere of radius $20$ cm will be :

• A. $25$ Vm
• B. $50$ Vm
• C. $100$ Vm
• D. $200$ Vm

Answer 1

Answer: (A)

$25$ Vm

Using Gauss's law, ${\varphi }_{10}=\frac{Q_{en}^{10}}{{ϵ}_0}$

or $Q_{en}^{10}=25{ϵ}_0$

Here for flux of radius 20 cm, $Q_{en}^{20}=Q_{en}^{10}=25{ϵ}_0$

thus, ${\varphi }_{20}=\frac{25{ϵ}_0}{{ϵ}_0}=25$ V-m