Question

4. Two point charges +4q and+q are placed 30cm apart. At what point on the line joining them the electric field is zero?
(a) 15cm from the charge q
(b) 7.5cm from the charge q
(c) 20cm from the charge 4q
(d) 5cm from the charge q​

Answer 1

Answer:

Let intensity of electric field be zero at distance x from charge q. Thus the point will be 30-x away from charge 4q. For electric field intensity to be equal, electric field due to two points should be equal. Thus this point will be 10 cm from +q and 30-10 = 20 cm from charge +4q.