Q.

Two metal spheres of radius R and 3R have same surface charge density σ. If they are brought in contact and then separated, the surface charge density on smaller and bigger sphere becomes σ1 and σ2, respectively. The ratio σ1σ2 is.          [2025]

1 19  
2 9  
3 13  
4 3  

Ans.

(4)

For conducting sphere, V=σrε0

After contact, V1=V2

σ1r1=σ2r2  σ1σ2=r2r1=3