Electromagnetic radiation - Wave nature

Whenever a charge is placed in an electric or a magnetic field, it experiences a certain force acting on it or if multiple charges are placed, they experience an interaction due to another. In the year 1870, James Maxwell became the first scientist to explain the interaction between the charges in the presence of the electric and magnetic fields. He proposed that when electrically charged particles perform an accelerating motion, alternating electrical and magnetic fields are produced and transmitted. These fields traverse in the forms of waves known as electromagnetic radiation.A light wave is an example of the electromagnetic radiation.

Electromagnetic radiation

Properties of electromagnetic radiation:

  1. The oscillating charged particles produce oscillating electric and magnetic fields which are perpendicular to each other and both are perpendicular to the direction of propagation of the wave.
  2. Electromagnetic waves do not require a medium i.e., they can travel in a vacuum too.
  3. There are many kinds of electromagnetic radiation, differing from one another in terms of wavelength or frequency. This electromagnetic radiation as a whole constitutes the electromagnetic spectrum. For example radio frequency region, microwave region, infrared region, ultraviolet region, visible region etc.
  4. The electromagnetic radiation is characterized based on various properties like frequency, wavelength, time period etc.

Frequency is defined as the number of waves that pass through a given point in one second. Mathematically it is equal to the reciprocal of the time period of electromagnetic radiation. A general equation relating the speed of light, frequency, and wavelength of an electromagnetic radiation is given below:

c = ν l

Where, c= speed of light,

ν= frequency of the electromagnetic wave and

l= wavelength of the electromagnetic wave.

Apart from frequency and wavelength, some other parameters are also used to categorize the electromagnetic radiation. One of these parameters is the wave number. Wave number is defined as the number of wavelengths per unit length. Mathematically, it is equal to the reciprocal of the wavelength. It is expressed in SI unit as m-1.

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Practise This Question

A 100 Watt bulb emits monochromatic light of wavelength 400 nm. Calculate the number of photons emitted per second by the bulb.