A sphere of radius 5 cm has a charge of 31.41 c. calculate the surface density of charge.

Soln:- given Q=31.41 c

And radius of sphere=5 cm=5×10^-2 m

Then area of sphere=4πr^2 

=4×3.141×(5×10^-2 m)^2

=4×3.141×25×10^-4 m^2

=25×4×3.141×10^-4 m^2

=100×3.141×10^-4 m^2

=3.141×10^-2 m^2

Now surface charge density=Q/A

=31.41 c/3.141×10^-2 m^2

=10^-3 c/m^2