A) 50 W infrared lamp
B) 1 W infrared lamp
C) 50 W ultraviolet lamp
D) 0.5 W infrared lamp
Correct Answer: C
Solution :
The minimum energy required for the emission of photoelectrons from a metal is called the work function of that metal and the corresponding wavelength is known as threshold wavelength. For ejection of photoelectrons the incident radiation should have wavelength smaller than\[5200{\AA}\]. Since, infrared radiation has wavelength greater than 8000 A, and ultraviolet has wavelength less than 4000 A, hence the 50 W ultraviolet lamp is used.
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