NEET Physics Notes Electromagnetic Wave – Properties of Electromagnetic Waves
Properties of Electromagnetic Waves
Properties of Electromagnetic Waves
If the electromagnetic wave is travelling along the positive direction of the X-axis, the electric field is oscillating parallel to the Y-axis and the magnetic field is oscillating parallel to the Z-axis
The rate of flow of energy in an electromagnetic wave, is described by the vector S called the Poynting vector, which is defined by the expression,
Its magnitude S is related to the rate, at which energy is transported by a wave across an unit area at any instant.
Transverse Nature of Electromagnetic Waves
According to Maxwell, electromagnetic waves consist of time varying electric and magnetic fields, which are perpendicular to each other, as well as direction of wave propagation.
Let us consider a plane of EM wave travelling in the x-direction and a rectangular parallelopiped OPQRSUVW placed with its edges, parallel to the three axes. The electric and magnetic fields, sinusoidally with x and t only, are independent of y and z. If the rectangular parallelopiped does not enclosed any charge, then according to Gauss’s law, the total electric flux across it must be zero i.e.
The possibility, Ex = Ex‘ predicts that electric field [E] remains the same at different points on X-axis, i.e. field is static. But static field cannot propagate a wave of finite wavelength, then Ex = Ex‘ =0 i.e. no component of E is parallel to the direction of wave propagation.
In other words, the electric field is perpendicular to the direction of propagation of EM wave.
By preceding the same manner holds time to the magnetic field, i.e. the magnetic field also perpendicular to direction of wave propagation, since both the electric and magnetic fields are perpendicular to the direction of wave propagation. Therefore, EM waves are transverse in nature.
Spectrum of Electromagnetic Radiation
The array obtained on arranging all the electromagnetic waves in an order on the basis of their wavelength is called the electromagnetic spectrum.
The spectrum of electromagnetic radiation has no upper or lower limits and all the regions overlap.
