Question

If two like charges of magnitude 1 × 10^–9 coulomb and 9 ×10^–9 coulomb are separated by a distance of 1 meter, then the point on the line joining the charges, where the force experienced by a charge placed at that point is zero, is-

• A. 0.25 m from the charge 1 × 10^–9coul
• B. 0.75 m from the charge 9 × 10^–9coul
• C. Both A and B
• D. At all points on the line joining the charges

Answer 1

Answer: (C)

Both A and B

Answer 2

Q Force on charge q is zero

$\therefore$F₂₁ = F₂₃

or $\frac { \mathrm { kqq } _ { 1 } } { \mathrm { x } ^ { 2 } }$ = $\frac { \mathrm { kqq } _ { 2 } } { ( 1 - \mathrm { x } ) ^ { 2 } }$

or $\frac { 1 \times 10 ^ { - 9 } } { \mathrm { x } ^ { 2 } }$ =

or $\frac { 1 } { x }$ = $\frac { 3 } { 1 - x }$

or 1 – x = 3x

or x = 0.25 m from 1 × 10^–9C

\ From 9 × 10^–9C, distance

= 1 – x

= 1 – 0.25

= 0.75