Given below are two statements:
Statement I : Out of microwaves, infrared rays and ultraviolet rays, ultraviolet rays are the most effective for the emission of electrons from a metallic surface.
Statement II : Above the threshold frequency, the maximum kinetic energy of photoelectrons is inversely proportional to the frequency of the incident light.
In the light of above statements, choose the correct answer from the options given below :
Statement I : Out of microwaves, infrared rays and ultraviolet rays, ultraviolet rays are the most effective for the emission of electrons from a metallic surface.
Statement II : Above the threshold frequency, the maximum kinetic energy of photoelectrons is inversely proportional to the frequency of the incident light.
In the light of above statements, choose the correct answer from the options given below :
- Both Statement I and Statement II are true
- Both Statement I and Statement II are false
- Statement I is true but Statement II is false
- Statement I is false but Statement II is true
The Correct Option is C
Solution and Explanation
Statement I: Ultraviolet (UV) rays have the highest frequency among the given options (microwaves, infrared rays, and ultraviolet rays). Since the energy of a photon is directly proportional to its frequency (\( E = h f \)), UV rays are the most effective for the emission of electrons from a metallic surface. Hence, Statement I is true.
Statement II: The maximum kinetic energy of photoelectrons is given by the photoelectric equation: \[ K.E_{\text{max}} = h f - h f_0, \] where \( h \) is Planck's constant, \( f \) is the frequency of the incident light, and \( f_0 \) is the threshold frequency. From the equation, it is clear that \( K.E_{\text{max}} \) is directly proportional to \( f \), not inversely proportional.
Hence, Statement II is false. Thus, the correct answer is \( \boxed{(3)} \).
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