Question

How will you divide a charge of 10 coulomb between two bodies such that
force of repulsion is maximum?
(a)3C,70 (b)4C,6C (c)10,9C (d) 5C,5C​

Answer 1

d) 5C, 5C

Explanation:

Let the total charge be Q,

One of the charge be q, then other charge will be (Q-q)

We know by coulomb's law,

F = K{q(Q-q)} / R²

differentiating wrt q,

dF/dq = K/R² *(Q-2q)

For maximum force of repulsion,

Put dF/dq=0

K/R² * (Q-2q)=0

Q=2q [K is constant]

q=Q/2

Here Q=10C,

then q=10/2= 5C.

Q-q= (10-5)=5C

d) (5C,5C) is the correct option.