Q.

The electric potential at the centre of two concentric half rings of radii R1 and R2, having same linear charge density λ is

1 2λε0  
2 λ2ε0  
3 λ4ε0  
4 λε0  

Ans.

(2)

dv=14πε0λ dℓR ;     v∫dv=14πε0λℓR

Potential at centre, V=V2+V1

⇒V=(λ.πR2)4πε0R2+(λ.πR1)4πε0R1=λ2ε0