NEET Physics Photo Electric Effect, X- Rays & Matter Waves NEET PYQ-Photo Electric Effect,X-Rays

  • question_answer
    A 5W source emits monochromatic light of wavelength \[5000\,\overset{o}{\mathop{A}}\,\]. When placed 0.5 m away, it liberates photoelectrons from a photosensitive metallic surface. When the source is moved to a distance of 1.0 m, the number of photoelectrons liberated will be reduced by a factor of:                                                         [AIPMT (S) 2007]

    A)  4         

    B)   8                   

    C)  16         

    D)  2

    Correct Answer: A

    Solution :

    Intensity of light is inversely proportional to square of distance.
    i.e.,       \[I\propto \,\,\frac{1}{{{r}^{2}}}\]
    or         \[\frac{{{I}_{2}}}{{{I}_{1}}}=\frac{{{({{r}_{1}})}^{2}}}{{{({{r}_{2}})}^{2}}}\]
                Given,   \[Given,{{r}_{1}}=0.5\,m,\,{{r}_{2}}=1.0\,m\]
                Therefore, \[\frac{{{I}_{2}}}{{{I}_{1}}}=\frac{{{(0.5)}^{2}}}{{{(1)}^{2}}}=\frac{1}{4}\]
    Now, since number of photoelectrons emitted per second is directly proportional to intensity, so number of electrons emitted would decrease by factor of 4.


You need to login to perform this action.
You will be redirected in 3 sec spinner