Question

Assertion : Photosensitivity of a metal is high if its work function is small.
Reason : Work function \[W = h{f_o}\] where \[{f_o}\] is the threshold Frequency.
(A) If both assertion and reason are true and reason is the correct explanation of assertion.
(B) If both assertion and reason are true but reason is not the correct explanation of assertion
(C) If assertion is true but reason is false
(D) If both assertion and reason are false

Answer 1

Hint:In order to solve this question, we should know that the photosensitivity of a metal and work function is in the context of the photoelectric effect here we will discuss the correctness of assertion and reason and then decide whether the reason is the correct explanation of assertion or not.



Complete answer:
We have given the Assertion: Photosensitivity of metal is high if its work function is small.
Work function of a metal is the minimum energy needed for metal to show photoelectric effect and smaller the work function more sensitive is the metal means the metal has higher photosensitivity hence, the assertion is correct.
Now, the Reason given is: Work function \[W = h{f_o}\] where \[{f_o}\] is the threshold Frequency so, the formula for work function is written correctly \[W = h{f_o}\] but, the reason is not the explanation for our assertion because the correct reason of assertion is that Photosensitivity of metal is high if its work function is small because work function is the minimum energy needed to show photoelectric effect and metal is more sensitive if it shows the photoelectric effect under minimum energy.
Therefor, the correct option is (B) If both assertion and reason are true but reason is not the correct explanation of assertion



Note:It should always be noted that, in the formula of work function \[W = h{f_o}\] h is known as the Plank’s constant and the complete equation for the photoelectric effect is given as $hf = h{f_o} + K.E$ where, ‘hf’ is the energy given to the metal and K.E is the kinetic energy acquired by the electrons.