Two point charges $q_1 = 4 μC$ & $q_2 = 9 μC$ are placed 20 cm apart. The electric field due to them will be zero on the line joining them at a distance of
Answer & explanation
Correct answer: option 1
Let electric field is zero at distance x from q1
⇒ $\frac{kq_1}{x^2} = \frac{kq_2}{(20-x)^2}$
⇒ $\frac{4}{x^2} = \frac{9}{(20-x)^2}$
⇒ $\frac{2}{x} = \pm \frac{3}{20-x}$
⇒ 40-2x = $\pm$ 3x
x = 8 cm from q1