A charged particle is moving in a uniform magnetic field in a circular path. Radius of circular path is $R$. When energy of particle is doubled, then new radius will be
A$R\sqrt 2 $
B$R\sqrt 3 $
C$2\, R$
D$3\, R$
Medium
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A$R\sqrt 2 $
a (a) $r = \frac{{\sqrt {2mK} }}{{qB}} \Rightarrow r \propto \sqrt K $ $ \Rightarrow \frac{R}{{{R_2}}} = \sqrt {\frac{K}{{2K}}} \Rightarrow {R_2} = R\sqrt 2 $
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