Wave Optics- 3

Question 1

what is unpolarised light

Answer 1

The resultant electromagnetic wave is a superposition of waves produced by the individual atomic sources and
it is called unpolarised light. In ordinary or unpolarised light, the vibrations of the electric vector occur symmetrically in all possible directions in a plane perpendicular to the direction of propagation of light.

Question 2

what does polaroid contain

Answer 2

A polaroid consists of long chain molecules aligned in a
particular direction.

The electric vectors (associated with the propagating
light wave) along the directions perpendicular to the aligned molecules get absorbed.

Thus, if an unpolarised light wave is incident on such a polaroid then the light wave will get linearly polarised with the electric vector oscillating
along a direction to the aligned molecules; this direction
is known as the pass-axis of the polaroid.

Question 3

define polarisation of light

Answer 3

The phenomenon of restricting the vibration of light (electric vector) in a particular direction perpendicular to
the direction of propagation of wave is called polarisation of light.

In polarised light, the vibration of the electric
vector occur in a plane perpendicular to the direction of propagation of light and are confined to a single
direction in the plane (do not occur symmetrically in all possible directions)

Question 4

PLANE OF POLARISATION AND PLANE OF VIBRATION :

Answer 4

The plane in which vibrations of light vector and the direction of propogation lie is known as plane of vibration

A plane normal to the plane of vibration and in which no vibration takes place is known as plane of polarisation

Question 5

polariser/analyser

Answer 5

First crystal A polarises the light so it is called polariser. Second crystal B, analyses the light whether it is
polarised or not, so it is called analyser.

i) nicol prism/tourmaline crystals/polaroid

Answer 6

Thus, if the light from an ordinary source (like a sodium lamp) passes
through a polaroid sheet P1, it is observed that its intensity is reduced by
half.

Question 7

parallel and crossed nicol prism

Answer 7

angle between the optic axes of 2 prisms is 0/180- parallel

When the angle between optic axes is 0- crossed

Question 8

Law of Malus

Answer 8

When a completely plane polarised light beam is incident on analyser, then intensity of emergent light varies as
the square of cosine of the angle between the planes of transmission axis of the analyser and the polarizer.

I α cos²ɸ
I = I₀ cos²ɸ