JEE Advanced 2020 Full Test 5 Paper 2

The charge distribution is shown in figure. Due to q1, the charge induction is non - uniform but net induced charge due to q1 is zero. At point A field is zero and potential is equal to the potential at center.

VA=VC=‌

1

4πε0

‌

q

R

+‌

1

4πε0

‌

q1

a

At point B, field is due to charge q only
EB=‌

1

4πε0

‌

q

y2

At point B, potential is due to charge q at center of cavity, −q induced on inner surface of cavity in addition to the potential at the center.
∴VB=‌

1

4πε0

[‌

q1

a

+‌

q

R

+‌

q

y

−‌

q

r

]