JEE Main & Advanced Sample Paper JEE Main Sample Paper-45

  • 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





    Correct Answer: C

    Solution :

     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,                 \[{{v}_{1}}>{{v}_{2}}\]

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