Tag: polarisation of light

Only for the ordinary ray the refractive index is observed to be constant in all directions

Nucleic acid is an optically active medium. When circularly polarized light passes through an absorbing optically active medium, the speeds between right and left polarizations differ as well as their wavelengths. This can be used to study the helical structure of nucleic acids.
An optical axis is a line along which there is some degree of rotational symmetry in an optical system. Thus it is a particular direction and not any
random line.

polaroid has absorption of O- Ray as the phenomenon behind its polarising ability.

Polaroid consists of needle - like crystals aligned in a particular direction.
Thus option C is correct answer.

calcite crystal display an optical property called birefringence. This causes objects viewed through a clear piece of calcite to appear doubled.
This is the reason one will see one dot rotating about the other.

In double - refraction the refractive index of the extra - ordinary ray varies according to the direction taken because it has components that  are both parallel and perpendicular to the crystal's optic axis. Thus (A) is correct.
The ordinary ray and the extraordinary ray are polarized in planes vibrating at right angles to each other. Thus (B) is correct.

For quartz crystal $\mu _{0}=1.544  ;  \mu _{e}=1.553$
For calacite crystal $\mu _{0}=1.658  ;  \mu _{e}=1.486$
Thus both a and b are true.

Huygens waves theory could well explain reflection, refraction and interference of light but could not explain the double refraction because in huygens principle light is considered as mechanical wave which could not explain the double refraction.

Some transparent crystals, such as tourmaline and calcite, have the property that when one views an object through them one sees two images of the object. If one passes a narrow beam of light through them, the refracted beam is split into two parts which travel through the crystal and emerge as two separate beams. One of the beams obeys the ordinary laws of refraction and is called the ordinary ray. The other beam is called the extraordinary ray. The extraordinary ray does not always lie in the plane of incidence. Its speed, and consequently its index of refraction, depends on its direction of propagation through the crystal.