Electromagnetic Radiation

Electromagnetic radiation is a spectrum that consists of radio waves, microwaves, infrared waves, visible light, ultraviolet radiation, X-rays, and gamma rays.

Electromagnetic radiation has a particle as well as a wave nature therefore this makes it interesting to study its nature in quantum theory.

Electromagnetic Radiation Properties

• The oscillating charged particles creates an oscillating electric and magnetic fields which are perpendicular or right angles to each other and both are perpendicular to the direction of propagation of the wave as well.

• Electromagnetic waves generally do not require a medium which means that they can travel in a vacuum.

• There are numerous types of electromagnetic radiation, that differ from one another in terms of their wavelength or frequency.

• Electromagnetic radiation is commonly categorized based on several properties such as frequency, wavelength, amplitude etc.

Electromagnetic Radiation Formula

Frequency is referred to as the number of waves that passes through a given point in one second. A general equation that is related to the speed of light, frequency, and wavelength of electromagnetic radiation is as follows:

c = ν 𝝀

Where,

• c represents the speed of light

• ν represents the frequency of the electromagnetic wave

• 𝝀 or lambda represents the wavelength of the electromagnetic wave.

Apart from the above-mentioned parameters frequency and wavelength, some other factors are also used to classify electromagnetic radiation. One of these factors is the wavenumber. Scientifically, the wavenumber is equal to the reciprocal of the wavelength. It is represented in the SI unit as m.

ν = 1/Wavelength

Dual Behaviour of Electromagnetic Radiation

Electromagnetic Radiation was assumed to have a wave nature only thus with the help of wave nature we can clearly explain a phenomenon like interference and diffraction. But Wave nature of Electromagnetic Radiation was unable to describe few things such as Black body radiation & the photoelectric effect.

In 1900, Planck stated the quantum theory and was successful in explaining blackbody radiation. According to this theory, atoms or molecules release or absorb energy only in discrete amounts termed as quantum. Quantum is referred to as the smallest amount of energy that is absorbed or released in the form of electromagnetic radiation.

Further, Einstein explained the Photoelectric effect by using Planck Quantum theory. He proposed that when a photon falls on the surface of a metal, then the complete photon’s energy is transferred to the electron.

Now based on the above observations of both Planck Quantum theory & Einstein Theory of Photoelectric effect, it was found that Electromagnetic Radiation behaves like particles or photons as well. Now the particle nature was not much reliable with the known wave nature of light. Consequently, this caused striking confusion among the scientists. The only solution to this problem was to accept the dual nature of Electromagnetic Radiation.

Thus, electromagnetic radiation posses dual nature;

Wave Nature

Particle Nature

Particle Nature of Electromagnetic Radiation

i. Photoelectric Effect

The photoelectric effect is referred to the emission of electrons when electromagnetic radiation, such as light, hits a substance. Electrons emitted in this effect are termed as photoelectrons. Though, this phenomenon of photoelectric effect can be explained only by the particle nature of light, in which light can be pictured as a stream of particles of electromagnetic energy. These particles of light are termed as photons.

Photons are explained below;

• Photons are elementary particles. It is referred to as a quantum of light.

• The energy of a photon is , E = hf Where h represents Planck’s constant F represents wave frequency E represents photon energy

• A photon generally remains unaffected by electric and magnetic fields. Photon is electrically neutral in nature.

• A photon is massless that is it has zero mass.

• Photons, unlike atoms can be formed or destroyed when radiation is produced or absorbed.

ii. Black Body Radiation

When the black body is heated, it becomes red-hot. In simple words, it releases red coloured light. When the temperature is increased further, then the colour of the radiation emitted changes as follows, first from red to yellow then to white and lastly to purple as the temperature increases. This states that the wavelength of radiation produced by the black body decreases with a rise in temperature.

Wave Nature of Electromagnetic Radiation

Wave theory of radiation was unable to explain the phenomena of the photoelectric effect and also the black body radiation.

Major points of electromagnetic wave theory include;

The energy that is emitted from a source is in the form of radiation and is also termed as radiant energy. These radiations comprise of electric and magnetic fields which oscillate perpendicular (or at right angles ) to each other and also is perpendicular to the direction of propagation of radiation.

These radiations or electromagnetic radiations (or electromagnetic waves) travel with the velocity of light and also possesses wave character.

Characteristics of a wave:

• Wavelength: The wavelength of a wave is referred to as the distance between two consecutive crest or trough It is represented by a symbol lambda ( 𝝀 ) and is generally expressed in cm or m.

• Frequency: The frequency of a wave is referred to as a number of waves that passes through a point in one second It is represented by a symbol v (nu) and is generally expressed in its SI unit that is hertz or abbreviated as Hz.

• Velocity: The velocity of a wave is referred to as the linear distance which is travelled by a wave in one second It is represented by a symbol v and is commonly expressed in centimetre per second or metre per second (cm/sec or m/sec).

• Amplitude: The amplitude of a wave is referred to as the height of the crest as well as the depth of trough true It is generally represented by symbol a and is expressed in the metre , centimetre or the units of length.

• Wavenumber: Wavenumber is referred to as the number of waves that is present in 1 cm length.