HEINRICH RUDOLF HERTZ ( – ) FIGURE . A linearly polarised electromagnetic wave, propagating in the z -direction with the oscillating electric field E along the x -direction and the oscillating magnetic field B along the y -direction. ω = ck , where, c = / μ ε [ . (a)] The relation ω = ck is the standard one for waves (see for example, Section .
of class XI Physics textbook). This relation is often written in terms of frequency, ν (= ω / π ) and wavelength, λ ( = π /k ) as c ν λ ⎛ ⎞ ⎜ ⎟ ⎝ ⎠ or νλ = c [ . (b)] It is also seen from Maxwell’s equations that the magnitude of the electric and the magnetic fields in an electromagnetic wave are related as B = ( E /c ) ( . ) We here make remarks on some features of electromagnetic waves.
They are self-sustaining oscillations of electric and magnetic fields in free space, or vacuum. They differ from all the other waves we have studied so far, in respect that no material medium is involved in the vibrations of the electric and magnetic fields. Sound waves in air are longitudinal waves of compression and rarefaction. Transverse waves on the surface of water consist of water moving up and down as the wave spreads horizontally and radially onwards.
Transverse elastic (sound) waves can also propagate in a solid, which is rigid and that resists shear. Scientists in the nineteenth century were so much used to this mechanical picture that they thought that there must be some medium pervading all space and all matter, which responds to electric and magnetic fields just as any elastic medium does. They called this medium ether . They were so convinced of the reality of this medium, that there is even a novel called The Poison Belt by Sir Arthur Conan Doyle (the creator of the famous detective Sherlock Holmes ) where the solar system is supposed to pass through a poisonous region of ether!
We now accept that no such physical medium is needed. The famous