(Q) The charge per unit length of four quadrant of a ring of radius R is 2λ, -2λ, λ and -λ respectively. The electric field at the centre is

(a) −(λ ÷ 2∏ε R) î

(b) (λ ÷ 2∏ε R) j

(c) (√2λ ÷ 4∏ε R) î

(d) None of the above

a     -(λ\ 2pie e r)

answer is 1. considering the centre to be at origin. electric field can be easily found out due to each quadrant. the net field along y axis is zero

Answer is (a)

Electric field due to circular ring at the centre is 

1st one is correct