Question

Two point charges +3 µC and +8 µC repel each other with a force of 40 N. If a charge of -5 µC is added to each of them, then force between them will become ______.

Options

• -10 N

• 10 N

• 20 N

• -20 N

Answer 1

Two point charges +3 µC and +8 µC repel each other with a force of 40 N. If a charge of -5 µC is added to each of them, then force between them will become -10 N.

Explanation:

Redistribution of charges takes place.

Charge q₁ = 3µC and Charge q₂ = 8µC

When third charge q3 = -5µC is added to each, then new charges on q₁ and q₂ will be

q₁ = 3 - 5 = -2µC

and q₂ = 8-5 = 3µC

Now,

Case I       `40=1/(4piepsilon_0)*(3xx8)/r^2`

Case I       `F=1/(4piepsilon_0)xx(-2xx3)/r^2`

`thereforeF/40=(-2xx3)/(3xx8)`

⇒ F = -10 N