Question

If the force between two charges is 9N, what will be the force if the distance between them is doubled and both the charges are increased to √2 times?

(a) 9N

(b) 4.5N

(c) 3N

(d) 3.75N

The question was posed to me in unit test.

This is a very interesting question from Coulomb’s Law topic in portion Charges and Fields of Physics – Class 12

Answer 1

Correct option is (b) 4.5N

Best explanation: The force will be 9*\(\frac {\sqrt2*\sqrt2}{2^2}\) N=4.5N because the force is proportional to the product of the two charges and inversely proportional to the square of the distance between them. Similarly, if the charges are the same but the distance is doubled, the force between them will be \(\frac {1}{4}\) times the previous value.