Question

The threshold wavelength for photoelectric emission from a material is $5200\mathring{A}$. Photoelectrons will be emitted when this material is illuminated with monochromatic radiation from a

• A. 50 W infrared lamp
• B. 1 W infrared lamp
• C. 50 W ultraviolet lamp
• D. 1 W ultraviolet lamp

Answer 1

Answer: (D)

1 W ultraviolet lamp

Answer 2

For photoemission to take place, wavelength of incident light should be less than the threshold wavelength. Wavelength of ultraviolet light $< 5200\mathring {A}$ while that of infrared radiation $> 5200\mathring {A}.$