Question

Two charges $40nC$ & $10nC$ are placed $60cm$ apart. At what point do we get the value of net electric field equal to zero?

• A. $10cm$ from $10nC$
• B. $20cm$ from $40nC$
• C. $20cm$ from $10nC$
• D. $40cm$ from $10nC$

Answer 1

The correct option is C $20cm$ from $10nC$

Let electric field $=0$ at point $P$ ($xcm$ from $10nC$)
$E=\frac{kq}{d^2}$ (field due to point charge)
$\frac{k(10\times {10}^{-9})}{x^2}=\frac{k(40\times {10}^{-9})}{(60-x{)}^2}$
$\frac{1}{x^2}=\frac{4}{(60-x{)}^2}$
$60-x=2x$
$60=3x$
$x=20cm$