Question

A charge q is placed at the centre of the line joining two equal charges Q. The system of the three charges will be in equilibrium. If q is equal to

• A. $- \frac{Q}{2}$
• B. $- \frac{Q}{4}$
• C. $+ \frac{Q}{4}$
• D. $+ \frac{Q}{2}$

Answer 1

Answer: (B)

$- \frac{Q}{4}$

Answer 2

By using Tricky formula $q = Q\left( \frac{x/2}{x} \right)^{2}$

⇒ $q = \frac{Q}{4}$ since q should be negative so $q = - \frac{Q}{4}$.