Question

Which of the following statements are correct, if the threshold frequency of caesium is $ 5.16 \times 10^{14} \, \text{Hz} $?

• A. When Cs is placed inside a vacuum chamber with an ammeter connected to it and yellow light is focused on Cs, the ammeter shows the presence of current.
• B. When the brightness of the yellow light is dimmed, the value of the current in the ammeter is reduced.
• C. When a red light is used instead of the yellow light, the current produced is higher with respect to the yellow light.
• D. When a blue light is used, the ammeter shows the formation of current.

Hint:

In the photoelectric effect, only light with a frequency greater than the threshold frequency can cause the ejection of electrons. Reducing light intensity reduces the current, but light with insufficient frequency (like red light) will not cause any emission of electrons.

Answer 1

The Correct Option is D

In the photoelectric effect, electrons are ejected from a material when light of a frequency greater than the threshold frequency strikes it. 
Option A: When yellow light (which has a frequency greater than the threshold frequency) is focused on caesium, electrons are ejected, and current flows. Therefore, this statement is correct. 
Option B: Dimming the brightness of the yellow light reduces the number of photons, which in turn decreases the number of electrons ejected. Hence, the current in the ammeter is reduced. This statement is correct. 
Option C: Red light has a frequency lower than the threshold frequency of caesium, so it does not have enough energy to eject electrons. Hence, no current will be produced. This statement is incorrect. 
Option D: Blue light has a frequency greater than the threshold frequency, so it will eject electrons and form current in the ammeter. This statement is correct. 
Thus, the correct answer is B, C, and D Only.