Two point charges and placed apart exert a force of on each other in vacuum

PHYSICS · Single correct · A Level · Physics · Fields and their consequences · Fields and their consequences

Problem

Two point charges

q_1 = 4\,\mu\text{C}

and

q_2 = 2\,\mu\text{C}

placed

0.30\,\text{m}

apart exert a force of

0.18\,\text{N}

on each other in vacuum. If

q_1

is increased to

12\,\mu\text{C}

and the separation is reduced to

0.20\,\text{m}

(keeping

q_2

unchanged), what is the new magnitude of the force? (a)

0.54\,\text{N}

(b)

0.81\,\text{N}

(c)

1.22\,\text{N}

(d)

0.24\,\text{N}