Speed of Electromagnetic Waves in Vacuum Formulae for NEET

Electromagnetic waves are created as a result of vibrations produced between an electric field and the magnetic field. The propagation of electromagnetic waves through the vacuum happens at a speed of 3 x 108ms-1 and the propagation of electromagnetic waves through any medium happens at a speed which is less than that of the speed in the vacuum.

1.Wave Number

k = 2π/λ

Where λ is the wavelength of the wave

2. Frequency 

The frequency of the wave f = ω/ 2π

Where ω is the angular frequency

3. The speed of the wave

v = λf

4.Maxwell’s Equations

Maxwells equation

5. Oscillating electric and magnetic field

E = Ex(t) = E0 sin (kz – wt)

Oscillations of electric and magnetic field

E0/B0 = c

C = 1/ c is the speed of light in vacuum

V = 1/ v is the speed of light in the medium

3. Electromagnetic Spectrum

Type Wavelength range Production Detection
Radio > 0.1 m Rapid acceleration and deacceleration of electrons in aerials Receiver aerials
Microwave 0.1 m to 1mm Klystron value and magnetron value Point contact diodes
Infra-red 1mm to 700nm Vibrations of atoms and molecules Infrared photographic film,Thermopile, Bolometer
Light 700nm to 400 nm When electrons move from one energy level to another it emis light. The eye, photocells, Photographic film
Ultraviolet 400 nm to 1 nm The electrons in inner shell moving from higher  energy level to lower eneergy level. Photocells photographic film
X-rays 1nm to 10-3 nm Inner shell electrons or X-ray tubes Geiger tubes, Ionisation chamber,Photographic film
Gamma Rays く10-3 nm Radioactive decay of the nucleus Observing the effect gamma-ray on the matter

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