Four point charges −Q, −q, 2q and 2Q are placed one at each corner of the square. The relation between Q and q for which potential at centre of square is zero is: [Diagram: Image]
Physics · Electrostatic · Electric Potential & Potential Energy
AIPMT Screening 2012 NEET Previous Year

Question

Four point charges −Q, −q, 2q and 2Q are placed one at each corner of the square. The relation between Q and q for which potential at centre of square is zero is: [Diagram: Image]

G1 Physics · Accepted Answer

Step 1: All square corners are equidistant from centre. Step 2: Centre potential V = (k/r)(−Q − q + 2q + 2Q) = k(Q + q)/r. Step 3: Set V = 0: Q + q = 0 ⇒ Q = −q.