Q: A mass m carrying a charge q is suspended from a string and placed in a uniform horizontal electric field of intensity E. The angle made by the string with the vertical in the equilibrium position is
(a) θ=tan-1 mg/Eq
(b) θ=tan-1 m/Eq
(c) θ= tan-1Eq/m
(d) θ=tan-1 Eq/mg
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Ans: (d)
Sol: $ T cos\theta = mg$
$ T sin\theta = qE $
On dividing
$ tan\theta = \frac{qE}{mg}$