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Solution


Q.

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 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.

E. When a white light is used, the ammeter shows formation of current.

Choose the correct answer from the options given below:                                 [2025]
1 A, D and E Only  
2 B, C and D Only  
3 A, C, D and E Only  
4 A, B, D and E Only  

Ans.

(4)

Threshold wavelength of Caesium (λ0) =cν0=3×1085.16×1014m
=0.58139×10-6m=581.39 nm

Photoelectric effect is observed if λ<λ0.  

(A) λyellow<λ0(581.39 nm), so yellow light shows photoelectric effect.

(B) When photoelectric effect is observed, then current is directly proportional to intensity of light. So when brightness of yellow light is reduced, the value of current in ammeter gets reduced.

(C) λred<λ0(581.39 nm), so the red light does not show photoelectric effect.

(D) λblue<λ0(581.39 nm), so the blue light shows photoelectric effect.

(E) White light has all frequencies. So, it has those wavelengths for which λ<λ0 and it shows photoelectric effect.