Let force per unit length required to tear shells is λ.
So, force required to tear shell of radius r1 is F1=λ2πr1 ---(1)
Also, E = Kqr2
and F1 ∝ q1Eo i.e. F1 ∝ r21E2o ---(2)
By (1) and (2)
In the same way,
λ2πr2=E2 r22 __(B)
By (A) ÷ (B)