Question

Electric force between two point charges q1 and q2 at rest is f.Now if a charge -q is placed next to q1.What will be the (a)force on q2 (b)total force on q2?

Answer 1

Given that,

Two point charges

First charge =q₁

Second charge = q₂

Electric force between two point charges q₁ and  q₂ at rest is f.

$f=\dfrac{1}{4\pi\epsilon_{0}}\dfrac{q_{1}q_{2}}{r^2}$

If a charge -q is placed next to q₁.

(I). We need to calculate the electric force on q₂

Using formula of electric force

$F'=\dfrac{kq_{2}(-q)}{r^2}$

Negative sign shows the direction of force.

(II). We need to calculate the total electric force on q₂

Using formula of electric force

$F_{net}=F_{q_{1}q_{2}}+F_{-q}q_{2}$

Put the value into the formula

$F_{net}=\dfrac{1}{4\pi\epsilon_{0}}\dfrac{q_{1}q_{2}}{r^2}+\dfrac{kq_{2}(-q)}{r^2}$

$F_{net}=f+F'$

Hence, (a). The electric force on q₂ is $\dfrac{kq_{2}(-q)}{r^2}$

(b). The total electric force on q₂ is $f+F'$