0.13 Chapter 4.light and matter – dielectric behaviour of matter  (Page 3/4)

Subsequently Focault measured the velocity of light in water. It turned out to be less than ‘c’. This was interoperated as some kind of drag effect by the water medium. This also contradicted Newton’s Corpuscular Theory of Light.

In 1845, Michael Faraday (1791-1867) established that a strong magnetic field could change the Polarization of Light Beam.

In 1861 and 1862, James Clerk Maxwell (1831-1879) synthesized the empirical knowledge of Gauss’s Divergence Theorem, Faraday Induction Law and Ampere’s Circuital Law into four differential equations and he established that Light was Electro-Magnetic Field propagating in all pervading aether as a transverse wave at a velocity c in vacuum:

In a dielectric medium the velocity of propagation (v) is:

Where n = refractive index of the material.

From (1a) it is evident that n = refractive index = √ε _r .

From Maxwell equations it was clear that Light was an Electro-Magnetic disturbance propagating out of a point source with the velocity of light with a spherical wave-front.

The Four Maxwell Equations in differential form are:

From (2), (3), (4) and (5) it is evident that:

1. There is a general perpendicularity of E and H;
2. The Maxwell Equations are symmetrical;
3. E and H are interdependent.

Time varying E field through (4) produces H field which is perpendicular to the direction of change of E and time varying H field through (3) produces E field which is perpendicular to the direction of change of H. So as an Electro-Magnetic disturbance is produced self sustaining transverse Electro-Magnetic Field travels out from the source of disturbance as shown in Figure 4.1. E and H are coupled in form of a pulse. E generates H farther out and H generates E still farther out. Thus E-M wave travels out in self sustained fashion and there is no need of aether. Still Maxwell assumed that there was an all pervading luminiferous aether which helped the propagation of E-M waves.

If a charge is accelerated in positive X-direction as shown in Figure 4.1. then a kink is produced in the Electric Field at (c.dt). This kink travels out at ‘c’. It has a radial as well as transverse component. Radial Component(electro-static component) diminishes as the square of r while Transverse Component(radiative component) diminishes as ‘r’. Hence after some distance r, only Transverse Component remains which detaches from the electric dipole and travels out as self-supporting E-M Radiative Field.

In 1888, Heinrich Rudolf Hertz(1857-1894) generated long E-M waves and published the results in the Philosophical Transactions of Royal Society of London.

In 1881, Michelson-Morley completed the measurement of velocity of light in different frames of reference but could detect no change in the standard value of ‘c’. Light velocity seemed to be invariant of the source of emission velocity.

Section 4.1.3. The Conceptual Paradigm Shift at the turn of 19 th and 20 th Century.

The invariance of the velocity of light to the Frame of Reference necessitated a paradigm shift in the theoretical framework given by Newtonian Relativity. Jules Henri Poicare(1854-1912) was the first to grasp this invariance and he expressed an alternative view point: