The ability of an element to form bonds with other atoms of the same element is called catenation.

It is the binding of an element to itself through covalent bonds to form chain or ring molecules.

Examples : Carbon is the most common element that exhibits catenation property. That means it can form long hydrocarbon chains and rings like benzene.

Huygen's Principle:

(i) Every point on a given wave front (called primary wave front) acts as a fresh source of new disturbance, called secondary wavelets which travel in all directions with the velocity of light in the medium.

(ii) The forward envelope of these secondary wavelets gives the new wave front at any instance.This is called secondary wave front.

Consider a plane wavefront AB incident on a surface PQ separating two media 1 and 2.
The medium 1 is a rarer medium of refractive index n1  in which light travels with a velocity C1  The medium 2 is a denser medium of refractive index n2  in which light travels with a velocity C2.

Giuseppe Mazzini was an Italian revolutionary who founded two underground societies; first Young Italy in Marseilles and then Young Europe in Berne.

Giuseppe Mazzini was an important figure in liberal natioanlism. He made a significant contribution to the unification of Italy.

By 1830, Giuseppe Mazzini put forward a coherent programme of a unitary Italian Republic formed a secret society named Young Italy to inspire them with ideas of unification.

Inspired by Mazzini several Secret societies sprang up in many European states to train revolutionaries and spread their ideas.

He inspired the youth of Italy with natioanlist ideas.

He believed God intended nations to be natural units of mankind and Italy could not continue to be a patchwork of small states and kingdoms.

He founded the underground secret societies Youth Italy Italy and Young Europe to involve the youth in revolutionary activities.

Coulomb’s Law

Coulomb’s law states that Force exerted between two point charges:

• Is inversely proportional to square of the distance between these charges and
• Is directly proportional to product of magnitude of the two charges
• Acts along the line joining the two point charges.

Brewster’s law:- Brewster’s law states that at any particular angle of incidence, reflected ray is completely polarized; and the angle between reflected and refracted ray is 90⁰.