Question

The threshold wavelength for photoelectric emission from a material is $5200\stackrel{\circ }{A}$. Photo-electrons will be emitted when this material is illuminated with monochromatic radiation from a

• A. 50 watt infrared lamp
• B. 1 watt infrared lamp
• C. 50 watt ultraviolet lamp
• D. 1 watt ultraviolet lamp
• E. Both (c) and (d)

Answer 1

The correct option is E

Both (c) and (d)

In this case, for photoelectric emission the wavelength of incident radiations must be less then $5200\stackrel{\circ }{A}$ . Wavelength of ultraviolet radiations is less then this value $\left(5200\stackrel{\circ }{A}\right)$ but wavelength of infrared radiations is higher than this value.