Dual Nature of Matter and Radiation
Dual nature of radiation and matter
The minimum amount of energy required by an electron to just escape from the metal surface is called the work function of the metal.
Electron Volt
One electron volt is the kinetic energy gained by an electron when it is accelerated through a potential difference of 1 volt.
Energy gained by an electron = Work done by electric field = qV
1 eV = 1.602 x 10-19 J
The electron volt is a commonly used unit of energy in atomic and nuclear physics.
Electron Emission
These phenomena of emission of electrons from a metal surface. For their release from the metal surface, electrons are supplied the required amount of energy by any one method:
Thermionic emission
Field emission or cold cathode emission
Photoelectric emission
Secondary emission
Dual nature of Light
In 1900, Planck proposed the quantization of EM waves and the existence of quanta of energy now called Photons.
Each photon has energy, E = hv
h: Planck’s constant
Where h = 6.626 x 10-34 J/s
= 4.136 x 10-15 eV/s
Photon travels in a straight line with a speed c= 299,792,458 m/s in vacuum. It is not a material particle but a packet of energy.
The energy of a photon depends on the frequency and does not change with medium.
E = hv = hc/λ
While changing medium speed and wavelength of photon changes but the frequency remains constant.
It is electrically neutral and is not affected by electric and magnetic fields.
It does not exist at rest, its rest mass is zero.
Equivalent mass of photon, E = mc2 = hv.
The momentum of the photon:
P = mc = (h/λc) x c
P = h/λ
The intensity of light is proportional to the number of photons in it.
The intensity of Light due to a Source
The energy crossing per unit area per unit time perpendicular to the direction of propagation is called the intensity of a wave.
Photon Flux
The number of photons incident on a normal surface per second per unit area.
Photoelectric Effect
If the light of suitable frequency illuminates a metal surface, electrons are emitted from the metal surface. The phenomenon is called the photoelectric effect. The photo (light)-generated electrons are called photoelectrons.
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