$A$ photon of energy $E$ ejects a photoelectron from a metal surface whose work function is $W_0.$ If this electron enters into a uniform magnetic field of induction $B$ in a direction perpendicular to the field and describes a circular path of radius $r,$ then the radius $r$ is given by (in the usual notation):

  • A
    $\sqrt {\frac{{2m\left( {E - {W_0}} \right)}}{{eB}}}$
  • B
    $\sqrt {2m\left( {E - {W_0}} \right)eB}$
  • C
    $\frac{{\sqrt {2e\left( {E - {W_0}} \right)} }}{{mB}}$
  • D
    $\frac{{\sqrt {2m\left( {E - {W_0}} \right)} }}{{eB}}$

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