Two pith balls each with mass m are suspended from insulating threads. When the pith balls are given equal positive charge Q, they hang in equilibrium as shown. We now increase the charge on the left pith ball from Q to 2Q while leaving its mass essentiality unchanged. Which of the following diagrams best represents the new equilibrium configuration?

Solution:
From Newton's Third Law of Motion forces acting on both the charges are equal.
\[ tan \theta = \frac{F}{mg} \]
So angle made by them with vertical will also be equal. But the value of θ will increase because force is increasing due to increase in charge.
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