Question

Two point charges $q_{1}$ and $q_{2}$ of magnitude $+10^{-8} C$ and $-10^{-8} C$ respectively are placed $0.1\, m$ apart. Calculate the electric field at point $P, 0.1\, m$ away from both the charges.

• A. $3.6 \times 10^{4} N C ^{-1}$
• B. $4 \times 10^{3} N C ^{-1}$
• C. $6 \times 10^{3} N C ^{-1}$
• D. $9 \times 10^{3} N C ^{-1}$

Answer 1

Answer: (D)

The point equidistant from both the charges will be on their perpendicular bisector as shown

$E_{1 C} =E_{2 C}=\frac{\left(9 \times 10^{9} N m ^{2} C ^{-2}\right)\left(10^{-8} C \right)}{(0.1 m )^{2}} $
$=9 \times 10^{3} N C ^{-1} $
$E_{C} =E_{1 C} \cos 60^{\circ}+E_{2 C} \cos 60^{\circ} $
$=2\left(9 \times 10^{3} N C ^{-1}\right) \times \frac{1}{2} $
$=9 \times 10^{3} N C ^{-1} $