Two identical thin metal plates A and B initially have charges q₁ and q₂ respectively ( q₁ > q₂ ). They are brought close to each other to form a parallel plate capacitor of capacitance C . If plate B is then connected to earth, the final potential of plate A is :

Step-by-step solution

When plate B is grounded, its potential becomes zero ( V_B = 0 ). For an ideal parallel plate capacitor, grounding one plate means the electric field outside the capacitor must be zero. Therefore, the charge on the outer surfaces of both plates becomes zero. Since plate A is isolated, its total charge remains q₁ . This entire charge q₁ must now reside on the inner surface of plate A . To maintain zero electric field inside the bulk of plate B , its inner surface must acquire a charge -q₁ from the earth. The potenti