Introduction To theories Of Light Flashcards
What is light?
Which branch of physics deals with the wave nature of light ?
Light is a form of energy which causes the sensation of vision.
Physical optics.
On what grounds were different theories of light proposed? Name the important ones. When is a theory considered to be correct?
Different theories on the nature of light were proposed on the basis that energy can be transferred from one point to another either by particle or wave motion.
Newtons corpuscular theory
Huygens wave theory
Maxwells electromagnetic theory
Max planck s quantum theory of radiation
A theory is considered to be correct if it can explain all the observable phenomenon of light
Who proposed the corpuscular theory?
Explain
What is a corpuscle
How does he explain vision and different colours of light?
The earliest theory was proposed by sir Isaac Newton in 1678. Acc. To the theory , light consists of a stream of extremely light and tiny material particles known as corpuscles (minute particles shot out from every point of a luminous body). These particles are shot out every point of a source of light with a very high speed. These corpuscles which travel in a straight line when fall on the retina produce the sensation of vision. Different colours of light were due to different sized corpuscles
What phenomenon did the corpuscular theory expln.
What are the demerits.
Rectilinear propagation reflection
However when the theory was applied to explain refraction of light , theoretical prediction on the velocity of light was that light travelled faster in a denser medium. This theoretical result was totally contradicted by the experimental results of Foucault and Michelson. Further it couldn’t explain interference diffraction polarisation.
Who proposed the wave theory of light
Explain
How does it explain vision and different colours?
Wave theory of light was proposed and developed by Christian Huygens in 1679
According to this theory every point on a luminous body acts as a source of disturbance. This disturbance is due to the vibrations of atoms and molecules of a source of light and this disturbance is propagated in the form of a longitudinal wave in a hypothetical medium called ether .it is assumed that ether pervades the entire universe. Energy is carried by the waves caused by the vibration of ether particles which possess high elasticity and low density. Energy which is distributed evenly in all direction when falls on the retina excites the optic nerve and sensation of vision is produced. Different colours were attributed to different wavelength of light waves.
What were the properties of ether?
What were the merits of Huygens’ theory?
Ether has high elasticity low density
Huygens theory could satisfactorily explain reflection refraction interference and diffraction ( on being modified by fresnel and young it could also explain polarisation). When the theory of light was used to explain refraction it predicted that the velocity if light in a rarer medium was greater than its velocity in a denser medium which was in agreement with the experimental results.
Who modified Huygens’ theory? What were the modifications and why?
Huygens theory could not explain polarisation of light
Fresnel and young suggested that light was a transverse wave and nota longitudinal wave as suggested by Huygens. This modification led them to explain polarisation also.
Further fresnel could also explain rectilinear property of light.
Demerits of Huygens theory
Although it could account for several phenomena of light the existence of ether was not experimentally established. Infant Michelson Morley experiment disproved the existence of ether.
It could not explain certain phenomena like photoelectric effect etc
Maxwells electromagnetic theory
Check text
Who proved the existence of electro magnetic waves
Heinrich hertz in 1888.
