Question

Two point charges A and B of magnitude +8 × 10-6 C and -8 × 10-6 C respectively are placed at a distance d apart. The electric field at the middle point O between the charges is 6.4 × 104 NC-1. The distance 'd' between the point charges A and B is:

• A. 2.0 m
• B. 3.0 m
• C. 1.0 m
• D. 4.0 m

Answer 1

Answer: (B)

3.0 m

Answer 2

The correct answer is (B) : 3.0 m

Fig.

Electric field at P will be
$E=\frac{kq}{(\frac{d}{2})^2}×2=\frac{8kq}{d^2}$
So,
$\frac{8×9×10^9×8×10^{−6}}{d^2}=6.4×10^4$
So, d = 3 m