10. Two point charges +4q and +q are kept at a distance of 30 cm from each other. At which point between them, the field intensity will be equal to zero? a) 15cm away from the +4q charge b) 20cm away from the +4q charge c) 7.5cm away from the +q charge d) 5cm away from the +q charge
Answer: b Explanation: The electric field at a distance of r from a charge q is equal to q4πεor2. Let the electric field intensity will be zero at a distance of x cm from +4q charge, so the fields due to the two charges will balance each other at that point. Therefore 4q4πεox2=q4πεo(30−x)2. Solving this we get x=20cm. Therefore the point will be 20cm away from the +4q charge.
