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
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
Updated On: Jun 14, 2022
- 50 W infrared lamp
- 1 W infrared lamp
- 50 W ultraviolet lamp
- 1 W ultraviolet lamp
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The Correct Option is D
Solution and Explanation
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}.$
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Concepts Used:
Photoelectric Effect
When light shines on a metal, electrons can be ejected from the surface of the metal in a phenomenon known as the photoelectric effect. This process is also often referred to as photoemission, and the electrons that are ejected from the metal are called photoelectrons.
Photoelectric Effect Formula:
According to Einstein’s explanation of the photoelectric effect :
The energy of photon = energy needed to remove an electron + kinetic energy of the emitted electron
i.e. hν = W + E
Where,
- h is Planck’s constant.
- ν is the frequency of the incident photon.
- W is a work function.
- E is the maximum kinetic energy of ejected electrons: 1/2 mv².
Laws of Photoelectric Effect:
- The photoelectric current is in direct proportion to the intensity of light, for a light of any given frequency; (γ > γ Th).
- There exists a certain minimum (energy) frequency for a given material, called threshold frequency, below which the discharge of photoelectrons stops completely, irrespective of how high the intensity of incident light is.
- The maximum kinetic energy of the photoelectrons increases with the increase in the frequency (provided frequency γ > γ Th exceeds the threshold limit) of the incident light. The maximum kinetic energy is free from the intensity of light.
- The process of photo-emission is an instantaneous process.