Question

Two point charges of $+3mC$ each are $100cm$ apart. At what point on the line joining the charges will the electric field intensity be zero?

• A. At one of the charges
• B. At the centre
• C. At the midpoint of centre and one of the charges
• D. At no point

Answer 1

The correct option is B At the centre

Field due to left charge $E_1=\frac{q}{4\pi {ϵ}_o{x}^2}$ rightward

Field due to right charge $E_2=\frac{q}{4\pi {ϵ}_o(r-x{)}^2}$ leftward

Net field at P$=E=E_1-E_2=0$

$⟹E_1=E_2$

$\frac{q}{4\pi {ϵ}_o{x}^2}=\frac{q}{4\pi {ϵ}_o(r-x{)}^2}$

$⟹x=r-x$

$⟹x=\frac{r}{2}$

Hence P is at center of line joining two charges.

Answer-(B)