Question

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

• A. $50$ watt infrared lamp
• B. $1$ watt infrared
• C. $1$ watt ultraviolet lamp
• D. $60$ watt infrared lamp

Answer 1

The correct option is C $1$ watt ultraviolet lamp

The threshold wavelength is $5200\dot{A}$. For a photoelectric emission to take place the wavelength of incident light must be less than the threshold value. The wavelength of UV rays is $100-4000\dot{A}$ . so Photoelectrons will be emitted when this material is illuminated with monochromatic radiation from a $1W$ ultraviolet lamp.