Question

Given below are two statements: one is labelled as Assertion (A) and the other one is labelled as Reason (R). 

Assertion (A): Emission of electrons in the photoelectric effect can be suppressed by applying a sufficiently negative electron potential to the photoemissive substance.

Reason (R): A negative electric potential, which stops the emission of electrons from the surface of a photoemissive substance, varies linearly with the frequency of incident radiation.

In light of the above statements, choose the most appropriate answer from the options given below:

• A. Both (A) and (R) are true but (R) is not the correct explanation of (A)
• B. (A) is true but (R) is false
• C. Both (A) and (R) are true and (R) is the correct explanation of (A)
• D. (A) is false but (R) is true

Hint:

In photoelectric effect, the stopping potential depends on the energy of incident photons, which in turn depends on the frequency of the radiation, but the relationship is not necessarily linear.

Answer 1

The Correct Option is A

Analysis of Assertion (A) and Reason (R):

Assertion (A): The statement claims that the emission of electrons in the photoelectric effect can be inhibited by applying a sufficiently negative electric potential to the photoemissive material. This is true because applying a negative potential, known as the stopping or retarding potential, counteracts the forward motion of the photo-emitted electrons, preventing them from reaching the anode.

Reason (R): The reason states that the negative electric potential required to stop the emission of electrons from the surface of a photoemissive substance varies linearly with the frequency of incident radiation. This is also correct. According to the photoelectric effect, the stopping potential \(V_0\) is related to the frequency \(ν\) of the incident radiation by the equation \(eV_0 = hν - φ\), where \(e\) is the electron charge, \(h\) is Planck's constant, and \(φ\) is the work function of the material. This equation indeed shows a linear relationship between the stopping potential and frequency.

Thus, both Assertion (A) and Reason (R) are true. However, while (R) is true and states a concept related to the photoelectric effect, it does not directly explain why applying a negative potential suppresses electron emission described in (A). The suppression is primarily due to the opposing electric field, not specifically because of the linear relationship with frequency.

Conclusion:

The correct answer is: Both (A) and (R) are true but (R) is not the correct explanation of (A).