Which of the following statements are correct, if the threshold frequency of caesium is 5.16×1014Hz ?
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 to 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.
E. When a white light is used, the ammeter shows formation of current.
Choose the correct answer from the options given below :
(A)A, D and E Only
(B)B, C and D Only
(C)A, C, D and E Only
(D)A, B, D and E Only✓ Correct
Answer: (D)
Solution
The threshold wavelength is λ0=ν0c=5.16×10143×108≈581nm, in the yellow region. A current flows only for light of wavelength at or below this value. Yellow light meets the condition and gives a current, and dimming it lowers the number of electrons ejected and so the current. Blue light, of shorter wavelength, and white light, which contains such wavelengths, also give a current. Red light, of longer wavelength than the threshold, ejects no electrons and gives no current. The correct statements are that yellow light produces a current, that dimming it reduces the current, that blue light produces a current and that white light produces a current.
JEE Main · 2025 · 07 Apr 2025 · Shift 1 · Single correct option
