CBSE Class 11-science Answered

Various theories of light;

The Corpuscular Theory

--- Created in the seventeenth century by Sir Isaac Newton 

--- States that light emitted by luminous objects consist of tiny particles of matter calledcorpuscles. When corpuscles hit a surface, each partice is reflected. 
--- Thought that light traveling from air into water will increase the speed, while light entering water will decrease the speed.

The Wave Theory

--- Discovered by Christian Huygens, a Dutch scientist, also in the seventeenth century 

--- States that light is emitted in a series of waves that spread out from a light source in all directions. These waves are not affected by gravity. 
--- Furthermore, he disagreed with Newton and said that light traveling from air to water willdecrease the speed, and vice versa. Huygens was proved later to be correct. 

--- 100 years later, Englishman Thomas Young competely disproved the corpuscular theory by showing that light waves can interfere with each other.

The Electromagnetic Theory

--- Discovered in the nineteenth century by James Maxwell 

--- Proposed that light waves do not require a medium for transmission. 
--- Light waves posses electrical and magnetic properties and can travel though a vacuum. Light waves are a part of a larger family of electromagnetic waves and make up the electromagnetic spectrum.

The Quantum Theory

--- Discovered by Max Planck, German scientist in 1900 

--- Stated that light waves travel as separate packets of energy called quanta or photons. --- Merged the subjects of the Corpuscular, Wave, and Electromagnetic Theories together.

Later, it was proved that the correct and most accurate theory was the Quantum Theory.