A) \[50\text{ }W\]infrared lamp
B) \[\text{1 }W\] infrared lamp
C) \[\text{50 }W\] ultraviolet lamp
D) \[\text{0}\text{.5 }W\] 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 \[5200\text{ }\overset{\text{o}}{\mathop{\text{A}}}\,\]. Since, infrared radiation has wavelength greater than \[8000\overset{\text{o}}{\mathop{\text{A}}}\,,\]and ultraviolet has wavelength less than \[4000\overset{\text{o}}{\mathop{\text{A}}}\,,\] hence the \[50\text{ }W\] ultraviolet lamp is used.
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