Dual Nature of Radiation and Matter: Work Function of Metals, Photoelectric Effect (For CBSE, ICSE, IAS, NET, NRA 2022)
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- The dual nature of matter and the dual nature of radiation were revolutionary concepts of physics.
- At the beginning of the twentieth century, scientists unravelled one of the best-kept secrets of nature – the wave particle duality or the dual nature of matter and radiation.
Work Function of Metals
- It is referred to minimum amount of energy required to take out one electron from the metal surface.
- So, This energy can be supplied through various sources such as a strong electric field or irradiation of light with a suitable frequency.
Photoelectric Effect
- It is the phenomenon in which the electrons are emitted from the metal surface when the light is illuminated in a suitable frequency.
- The photoelectric effect is the conversion of light to electrical energy.
- It follows the law of conservation of energy and is an instantaneous process.
- Photoelectric current depends upon three factors:
- The potential difference applied within the two electrodes
- The incident light՚s intensity
- The nature of the emitter material
- Factors affecting stopping potential
- The incident light՚s frequency
- The emitter material՚s nature
- The frequency of the incident light does not depend on the intensity.
- Stopping potential is directly proportional to the kinetic energy of the emitted electrons.
Laws of Photoelectric Effect
The laws of the Photoelectric effect are as follows:
- For a given metal and frequency of incident light, the photoelectric current is directly proportional to the intensity of incident light.
- For a given metal, there is a certain minimum frequency, called Threshold frequency, below which there is no photo-electric emission.
- The maximum kinetic energy of photoelectrons above a threshold frequency depends upon the frequency of incident light.
- The photoelectric emission is an instantaneous process.
Heisenberg՚S Uncertainty Principle
- Its Principle states that both the momentum and position of a particle cannot be determined simultaneously.
- Mathematically, it can be expressed as ∆ x ∆ P ⩾ (h/4π) where ∆ x represents the Uncertainty in position, ∆ P represents the Uncertainty in Momentum.
Quanta or Photon
- Light is composed of various discreet packs of energy which are called quanta.
- Einstein explained the photoelectric effect on the basis of this theory. Each photon posses an energy E = (hv) and momentum and it depends on the frequency (v) of light incident and never on the intensity.
- In metal surface, photoelectric emission occurs due to the photon absorption capability of an electron.
Electronic Emission
- Minimum energy that is required to emit an electron from the surface of a metal can be supplied to the free electrons by either of the three methods given below:
- Thermionic Emission: Required thermal energy is provided to the free electrons by suitably heating it so as to enable them to come out of the metal.
- Field Emission: Electrons are kept under the strong influence of the electric field to emit the electron out of the metal.
- Photo-electric Emission: When the light of appropriate frequency is made to illuminate a metal surface, electrons are emitted from it. These photo-generated electrons are called Photoelectrons.