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1. Electric Charges and Fields
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Time period of a block suspended from the upper plate of a parallel plate capacitor by a spring of stiffness $k$ is $T$. When block is uncharged. If a charge $q$ is given to the block them, the new time period of oscillation will be
A
$T$
B
$ > T$
C
$ < T$
D
$ \ge T$
Solution
(a) The forces that act on the block are $qE$ and $mg$. Since $qE$ and $mg$ are constant forces, the only variable elastic force changes by $kx$. Where $x$ is the elongation in the spring $ \Rightarrow $ unbalanced (restoring) force $ = F = – kx$
$ \Rightarrow $ $ – m{\omega ^2}X = – KX$$ \Rightarrow $ $\omega = \sqrt {\frac{k}{M}} = T$.
Standard 12
Physics
