# 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.

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