Write down the properties of electromagnetic waves.

Explanation

(i) Electromagnetic waves are produced by any accelerated charge.
(ii) Electromagnetic waves do not require any medium for propagation. So electromagnetic wave is a non-mechanical wave.
(iiI) Electromagnetic waves are transverse in nature.
(iv) Electromagnetic waves travel with speed which is eqaul to the speed of light in vacuum or free space,
` c = (1)/(sqrt(epsilon_(0)mu_(0))) = 3 xx 10^(8) ms^(-1),` where `epsilon_(0)` is the permittivity of free space or vacuum and `mu_(o)` is the permeability of free space or vacuum.
(v) The speed of electromagnetic wave is less than speed in free space or vacuum, that is v `lt` c. in a medium of refractive index, `mu = sqrt(epsilon_(r ) mu_(r ))` where `epsilon_(r )` is the relative permittivity of the medium (also known as dielectric constant ) and `mu_(r )` is the realative permeability of the medium.
(vi) Electromagnetic waves are not deflected by electric field or magnetic field.
(vii) Electromagnetic waves can show interference, diffraction and can also be polarized.
(viii) The energy density of the electromagnetic wave is
`mu = (1)/(2) epsilon_(0) E^(2) = (1)/(2) (1)/(mu_(0)) B^(2) , mu = epsilon_(0) E^(2) = (1)/(mu_(0)) B^(2)`
(ix) The average energy density for electromagnetic wave,
`(mu) = (1)/(2) epsilon_(0)E^(2) = (1)/(2) (1)/(mu_(0)) B^(2)`
(x) The energy crossing per unit area per unit time and perpendicular to the direction of propagation of electromagnetic wave is called the intensity.
Intensity, I = [`mu`] c or
`I = ("total electromagnetic energy")/("Surface area (A)"xx time (t)) `
`("Power")/("surface area (A)")`
(xi) electromagnetic waves carry energy and momentum . `("energy")/(speed) = (U)/(c )`
the force exerted by an electromagnetic wave on unit area of a surface is called radiation pressure.
(xii) if the electromagnetic wave incident on a material surface is completely absorbed, then the energy delivered is U and momentum imparted on the surface is
`P = (U)/(c )`
(xiii) If the incident electromagnetic wave of energy U is totally reflected from the surface , then the momentum delivered to
the surface is `Delta`P = `(U)/(c ) - (- (U)/(c )) = 2 (U)/( c)`
(xiv) the rate of flow of energy crossing a unit area is known as pointing vector for electromagnetic waves.
(xv) Electromagnetic waves carries not only energy and momentum but also angular momentum.