• Angular momentum of EM waves can be understood in simple way. Consider a setup of oppositely-charged coaxial cylindrical shells and in between them a solenoid is kept. An AC current is flowing through it and when the current in the solenoid is reduced to zero, then the inner and outer cylindrical shells start to rotate in opposite directions. The rotation of these cylinders is due to the impart of angular momentum from the electromagnetic field produced by the AC current.
12th - 12th - - - - - Unit Electromagnetic waves particle accelerates, it produces magnetic field in addition to electric field. Both electric and magnetic fields are time varying fields. Since the electromagnetic waves are transverse waves, the direction of propagation of electromagnetic waves is perpendicular to the planes containing electric and magnetic field vectors. Any oscillatory motion is also an accelerated motion.
So, when the charge oscillates (oscillating molecular dipole) about their mean position (Figure . ), it produces electromagnetic waves. Suppose the electromagnetic field in free space propagates along z -direction and if the electric field vector points along x -axis, then the magnetic field vector will be mutually perpendicular to both electric field and the direction of wave propagation. Thus kz t x = sin ω kz t y = sin ω where E o and B o are amplitudes of oscillating electric and magnetic field, k is a wave number, ω is the angular frequency of the EXAMPLE .
The relative magnetic permeability of the medium is . and the relative electrical permittivity of the medium is . . Compute the refractive index of the medium.
Solution Dielectric constant (relative permittivity of the medium), e r = . Magnetic permeability, µ r = . Refractive index of the medium, n e µ . .
Sources of electromagnetic waves Any stationary charge produces only electric field (refer Unit ). When the charge moves with uniform velocity, it produces steady current which gives rise to magnetic field (not time dependent, only space dependent)