• # question_answer Direction: Light having photons energy $hv$ is incident on a metallic plate having work function $\phi$ to eject the electrons. The most energetic electrons are then allowed to enter in a region of uniform magnetic field B as shown in the figure.   The electrons are projected in XZ-plane making an angle of$\theta$ with X-axis and magnetic field is $\mathbf{B}={{B}_{0}}\,i$ along X-axis. Maximum pitch of the helix described by electron is found to be p. Take mass of electron as m and charge as q. Based on above information, answer the following questions The plot between X-coordinates of location of electron as a function of time for different frequencies v of the incident light, is A)        B)   C)         D)

According to figure, ${{x}_{1}}>{{x}_{2}}$ and                  ${{t}_{1}}<{{t}_{2}}$ $\therefore$                ${{v}_{1}}=\frac{{{x}_{1}}}{{{t}_{1}}}$ and                  ${{v}_{2}}=\frac{{{x}_{2}}}{{{t}_{2}}}$ thus,                 ${{v}_{1}}>{{v}_{2}}$