State six characteristics of electromagnetic waves. What is Greenhouse effect ?

Explanation

Characterics (or) properties of electromagnetic waves :
1) Electromagnetic waves do not require any material medium for their propagation . They propagate in vaccum as well as in a medium.
2) Speed of E.M. waves in free space (or) vacuum is given by
`C=(1)/(sqrt(mu_(0)epsi_(0)))=3xx10^(8) ` m/s
3) Speed of E.M waves in a medium is given by
`v=(1)/(sqrt(muepsi))`
4) Electromagnetic waves are transverse in nature.
Electric field `vecE` and magnetic field `vec B` which constitue the E.M waves an mutually perpendicular to each other as well as perpendicular to the direction of propagation of the wave.
5) Electromagnetic waves are self sustaining electric and magnetic field oscillations in space.
6) Electromagnetic waves transport energy .
Poynting vector `(vecP)=(1)/(mu_(0))(vecE xx vecB)`
7) Relation between electric field vector `vecE` and magnetic field `vecB` in vacuum is given by `C=(E_(0))/(B_(0))` .
8) Electromagnetic waves are not deflected by magnetic and electric fields.
9) Electricmagnetic waves can be reflected, refracted , interferenced , diffracted and polarised.
10) Electromagnetic wave follow the superposition principle.
11) Average electric energy density of E.M wave is given by
` U_(av)=U_(E)+U_(B)`
`U_(av)=(1)/(2)epsi_(0)E^(2)+(1)/(2)(B^(2))/(mu_(0))`
`U_(av)=2U_(E)=2U_(B)`
12) Intensity of an E.M waves depends on its average energy density .
`I=(1)/(2)epsi_(0)C E_(0)^(2)`
13) E.M waves carry momentum and exert radiation pressure is given by
`P=(F)/(A)=(1)/(A)(dp)/(dt)=("Intensity" (I))/(C)`
Green house effect :
The temperature of the Earth increases due to radiation emitted by the Earth is trapped by atmosphere gases like `CO_(2), CH_(4), N_(2)O`, Chlorofluoro carbons etc is called green house effect.