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): Applying a sufficiently negative electric potential to a photoemissive material will stop electron emission in the photoelectric effect. This is correct because the negative potential (stopping or retarding potential) opposes the movement of photo-emitted electrons, preventing them from reaching the anode.

Reason (R): The negative electric potential needed to stop electron emission from a photoemissive surface is linearly dependent on the incident radiation's frequency. This is also correct. The photoelectric effect equation \(eV_0 = hν - φ\) shows that stopping potential \(V_0\) has a linear relationship with frequency \(ν\), where \(e\) is electron charge, \(h\) is Planck's constant, and \(φ\) is the work function.

Both Assertion (A) and Reason (R) are true. However, Reason (R), while true and related to the photoelectric effect, does not explain Assertion (A). The reason electron emission is suppressed in (A) is the opposing electric field, not the linear relationship between stopping potential and frequency.

Conclusion:

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