Question

Two particles $A$ and $B$ having charges $20 \,\mu C$ and $-5 \,\mu C$ respectively are held fixed with a separation of $5 \,cm$. At what position a third charged particle should be placed so that it does not experience a net electric force?

• A. At $5 \,cm$ from $20 \,\mu C$ on the left side of system
• B. At $5\, cm$ from $-5\, \mu C$ on the right side
• C. At $1.25 cm$ from $-5 \,\mu C$ between two charges
• D. At midpoint between two charges

Answer 1

Answer: (B)

$E _{ N }=+\frac{ k (-5\, \mu C )}{ x ^{2}}+\frac{ k (20\, \mu C )}{(5+ x )^{2}}=0$
$x = 5\,cm$