Question

A ball of mass $0.5gm$ carries a positive charge of magnitude $10\mu C.$ it is suspended by a thread in a downward electric field of intensity $300N/C,$ the tension in the spring is:

• A. $5\times {10}^{-3}N$
• B. $8\times {10}^{-3}N$
• C. $2\times {10}^{-3}N$
• D. Zero

Answer 1

The correct option is B $8\times {10}^{-3}N$

i) Gravitation force / pull

2) Coulombic force

and the tension will be resultant of these two forces.

$\therefore$ ATQ, gravitational force $=0.5gN$

$=5\times {10}^{-3}N$

For coloumbic force $F_c=q\overrightarrow{E}$

$=10\times {10}^{-6}\times 300=3\times {10}^{-3}N$

$\therefore$ The resultant force will be $=5\times {10}^{-3}+3\times {10}^{-3}=8\times {10}^{-3}N$

$\therefore$ Option (B) is the correct answer.