^What is light?
In general light means following three parts
As these are parts of EM spectrum, thus light is electromagnetic, thus properties of light are same as that of any EM wave. Light can behave like a ray, a wave & as a particle, depending on its interaction with the objects it encounters on its way.
^Electromagnetic Force
EM – force acts between charged particles. It binds electrons with nuclei to form atoms & binds atoms together to form molecules. It is responsible for the properties of solids, liquids, & gases. Force of attraction/repulsion between two static charges is described by the Coulomb’s law i.e 
Electric forces and magnetic forces were considered to be separate forces until the 1860s when James Clerk Maxwell was able to demonstrate that they were different manifestations of the same force – the electromagnetic force. Infact, all contact forces such as: Frictional force (f), Viscous force (Fv), Air drag (fd) Spring force (Fspring or Fr), Normal reaction (N), Tension force in ropes, strings & muscles (T), Buoyant force (B or U), Surface tension force (FS) are actually due to the electromagnetic force.
^Maxwell equations
Following five equations give a complete description of all em– interactions and are called Maxwell eq:
^γ – rays
(a) Produced in nuclear reactions and are also emitted by radioactive nuclei (such as Co 60 & Cs 137).
(b) Properties: Effect on photographic plate, fluorescence, ionization, diffraction, high penetrating power & can cause serious damage if absorbed by living tissues.
(c) Used
^Ultraviolet light
(a) Produced by special lamps like mercury and iron are lamps and by very hot bodies like sun.
(b) Properties: Effect on photographic plate, fluorescence, ionization, highly energetic, tanning of the human skin.
(c) Used
^Visible light
^Infra red waves
(a) Also called heat waves & are produced by hot bodies and molecules.
(b) Properties: Heating effect, reflection, refraction, diffraction & propagation through fog.
(c) Used
^Micro waves
(a) Produced by special vacuum tubes like klystrons & magnetrons. Due to their shorter wavelengths the microwaves don’t spread or bend around the corners of any obstacle coming in their way, hence can be transmitted as beam signals in a particular direction.
(b) Properties: Reflection, refraction, diffraction and polarization.
(c) Used in
Diamagnetism
Diamagnetics are temporary weak magnets posses magnetism only when placed in external magnetising field. It is found in the atoms or molecules having even number of electrons. In the unmagnetized form of a diamagnetic the magnetic moments of the two electrons having same value of principle quantum number ‘n’ have equal & opposite value cancel out, thus producing net zero magnetic moment. However when placed in an external magnetic field the electron having dipole moment opposite to external magnetic field is accelerated & other one retards, producing a net non zero magnetic moment in a direction opposite to the applied magnetic field. Diamagneitcs get repelled weakly by magnetizing fields. Now when external magnetic field is switched off, the magnetic force on electrons again becomes zero, due to which the two magnetic moments again become equal & cancel each other.
Cause of magnetism
1. Electrons, protons, neutrons all posses magnetic moment 
due to both orbital & spin motions. This magnetic moment is ultimately responsible for magnetism.
2. due to spin is also called intrinsic magnetic moment or permanent magnetic moment & can be understood using quantum mechanics only.
3. associated with the orbital motion of a charge can be explained even by classical concepts, for it an electron orbiting around a nucleus in a circle or radius r at a velocity v it is 
4. The minimum value of produced due to the orbital motion of an electron around an atomic nucleus is called Bohr magneton (μ).
5. The nuclear magnetic moment typically is much smaller than the electron magnetic moment 
.
6. Net magnetic moment of an atom is the vector sum of is magnetic moments of all of its electrons, protons & neutrons, both due to orbital motion & as well as spin motion.
7. Generally magnetic moments of atoms are randomly aligned & thus for any volume containing more than several thousand atoms net dipole moment is usually zero (for all types of material, dia, para, ferro).
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