2 Electromagnetic Waves
Electromagnetic Waves
Sources of Electromagnetic Waves
- Accelerated charges radiate electromagnetic waves − Maxwell’s theory.
- Frequency of the electromagnetic wave naturally equals the frequency of oscillation of the charge.
Nature of Electromagnetic Waves
- Electric and magnetic fields in an electromagnetic wave are perpendicular to each other and to the direction of propagation.
- Electric fieldEx and magnetic field By are perpendicular to each other and to the direction z of propagation.
∴ Ex = E0 sin (kz − ωt) …. (i)
By = B0 sin (kz − ωt) …. (ii)
Where,
ω − Angular frequency
k − Wave/propagation vector
λ − Wave length
t − Time
- Speed of propagation ofwave is ω/ Using equations (i) and (ii) and Maxwell’s equations, we obtain
ω = c k
Where, 
- The magnitude of the electric and magnetic fields in an electromagnetic wave are related as
- Velocity of light in material medium:
Where,
∈ − Permittivity of material medium
μ − Permeability of material medium
- Electromagnetic waves carry energy and momentum and it also exerts pressure, called radiation pressure.
- When the total energy (U) is transferred to a surface in time t, the magnitude of the total momentum delivered to the surface is
Where,
c− Speed of light