The electric field in a region is radially outward with magnitude E=αr. Calculate the charge contained in a sphere of radius R centered at the origin. Calculate the value of the charge if α=100Vm−2 and R=0.30 m.
Consider a spherical shell of radius x. The electric flux through this surface is
ϕ=∫s→E⋅d→S=Er4πr2
Therefore, the electric flux through spherical surface of radius R will be
ϕ=ER4πR2
When r=R,ER=αR, we have ϕ=αR4πR2By Gauss theorem, net electric flux is 1ε0×change enclosed
∴αR4πR2=1ε0Qenclosedor Qenclosed=(4πε0)αR3
Given R=0.30 m, α=100Vm−2
Qenclosed=19×109×100×(0.30)3=3×10−10C