Initially, it was believed that matter possessed particle nature. Various properties of light were explained by considering light as a particle. Later, it was found experimentally that matter does possess the properties of a wave. Hence it was concluded that matter has dual nature .i.e.both particle as well as a wave.
In quantum mechanics, the dual nature of matter is considered as an important topic. Every particle or quantum entity is either expressed as a wave or a particle in quantum mechanics. Maxwell’s equation of electromagnetism and experiments by Hertz on the generation and detection of electromagnetic strongly established the wave nature of light. Dual nature of matter further helps in modifying the inabilities of classical mechanics.
Photoelectric effect
The photoelectric effect is an important concept explained considering the dual nature of matter. The photoelectric effect is a phenomenon of emission of electrons from the surface of metals when the light of suitable frequency is incident on the metal surface. The electrons that get emitted from the metal surface are called photoelectrons. What happens in the process is that the electrons on the surface of the metal absorb enough energy from the incident light, so as to overcome the attractive forces that bind them to the nuclei.
Some Important terms in Photoelectric effect
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- Threshold Frequency: The minimum frequency of the incident radiation below which photoelectric emission completely ceases is known as the threshold frequency.
- Work Function: Work function of a photo metal is the minimum energy required to just liberate an electron from the metal surface.
- Threshold Wavelength: The maximum wavelength of the incident radiation that can cause an electron to emit from the surface of the metal.
- Stopping potential: It is the potential required to stop emission of electrons from a metal surface when an incident beam of energy greater than the work potential of metal is incident on it.
Laws of Photoelectric effect
- The photoelectric emission is an instantaneous process. The time interval between the incidence of radiation on the photo metal and the emission of electrons from its surface is of the order of 10-9 second.
- For every given photo material, there is a particular frequency below which photoelectric emission does not take place. This frequency is called the threshold frequency.
- The number of photoelectrons emitted is directly proportional to the intensity of radiation.
- The maximum kinetic energy of the emitted electrons is directly proportional to the frequency of the radiation but is independent of the intensity of the radiation.
Characteristics of the Photoelectric effect
- The threshold frequency is different for different materials
- The photoelectric current is directly proportional to the intensity of light.
- The kinetic energy of the emitted electron is directly proportional to the frequency of the radiation.
- The process is instantaneous.
Application of photoelectric effect
- The photoelectric effect is used in devices like the photo-emissive cell, photovoltaic cell, photoconductive cell and solar cells.
- This effect is used in the photoelectric sensors used in digital cameras
- Photoelectric smoke detectors work on the phenomenon of photoelectric effect.
- Solar panels are a series of metallic plates that face the sun and exploit the photoelectric effect.
