Question

Two identical pendulums $A$ and $B$ are suspended from the same point. Both are given a positive charge, with $A$ having more charge than $B$. They diverge and reach equilibrium with the strings of pendulums $A$ and $B$ making angles ${\theta }_1$ and ${\theta }_2$ with the vertical respectively. Then:

• A. ${\theta }_1$ > ${\theta }_2$
• B. ${\theta }_1={\theta }_2$
• C. ${\theta }_1$ < ${\theta }_2$
• D. the tension in A is greater than that in B

Answer 1

Answer: (B)

Coulomb's electrostatic force acting on 2 charged particles is equal if they are kept isolated.

i.e it doesn't matter which bob has more charge, the force acting between them will still be the same and thus they will make the same angle from the vertical.

From Coulomb's law, the force acting on both the particles will be

F $=\frac{kQq}{r^2}$

Hence , $T_1=T_2$ , which implies ${\theta }_1={\theta }_2$.