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.Maxwell’s Equations

Maxwells equation

2. 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


Wavelength range




> 0.1 m

Rapid acceleration and deacceleration of electrons in aerials

Receiver aerials


0.1 m to 1mm

Klystron value and magnetron value

Point contact diodes


1mm to 700nm

Vibrations of atoms and molecules

Thermopile, Bolometer, Infrared photographic film


700nm to 400 nm

Electrons in atoms emit light when they move from one energy level to a lower energy

The eye, photocells, Photographic film


400 nm to 1 nm

Inner shell electrons in atoms moving from one energy level to a lower level

Photocells photographic film


1nm to 10-3 nm

X-ray tubes or inner shell electrons

Photographic film, Geiger tubes, Ionisation chamber

Gamma Rays

く10-3 nm

Radioactive decay of the nucleus

Observing the effect gamma-ray on the matter