Q.

A spherical portion has been removed from a solid sphere having a charge distributed uniformly in its volume, as shown in the figure. The electric field inside the emptied space is           [2007]

1 zero everywhere  
2 non-zero and uniform  
3 non-uniform  
4 zero only at its center  

Ans.

(2)

Let the charge per unit volume be σ and O be the centre of a uniformly charged solid sphere. Let us consider a uniformly charged sphere of negative charge density σhaving its centre at O'. Also let OO' be equal to a.

Let us consider an arbitrary point P in the small sphere. The electric field due to charge on the big sphere using Gauss's theorem E1=σ3ε0r1

Also the electric field due to the small sphere

E2=σ3ε0r2

  The total electric field

E=E1+E2=σ3ε0a

Hence the electric field will have a finite non-zero value which will be uniform.