Question

The tourmaline crystal
A. Absorbs ordinary light and transmits extra ordinary
B. Absorbs extra ordinary light and transmits ordinary light
C. Both absorb ordinary light and extra ordinary light.
D. Both transmit ordinary light and extra ordinary light.

Answer 1

When light falls on the c axis of tourmaline crystal i.e., the longest direction between a crystal’s sides, the rays of light which have polarisation along the optical axis of the medium is transmitted known as extra ordinary light.

Complete step by step answer:
A tourmaline is a crystalline boron silicate mineral which is compounded with elements such as aluminium, iron, magnesium, sodium, etc. It is a semi-precious stone and generally found in black colour but the colour can vary from colourless to different colours such as brown, red, yellow, etc. It is a six member ring that is having a trigonal crystal shape.
Tourmaline is easily identified as finished stones have a soft lustre and it has two refractive indexes 1.620 and 1.640 which allow for some doubling of back facets and inclusions in the stone. It shows some long tubes that are oriented parallel to the c-axis of the crystal. The tourmaline absorbs ordinary light along the c-axis of the crystal and if we look at a transparent tourmaline crystal from all the directions that are perpendicular to the c-axis, a striking effect will be produced by it.
It absorbs ordinary light and transmits extra ordinary light of different colours. When a beam of plane polarised light is incident normally on a plate of tourmaline cut parallel to the optical axis, it will be absorbed or transmitted depending on whether the axis of tourmaline is parallel or perpendicular to the plane of polarisation of the incident light. The ordinary light is parallel to the axis and thus it is absorbed and extraordinary light is perpendicular which is transmitted by it.

So, the correct answer is “Option A”.

Note:
The tourmaline crystal allows the ordinary rays of light to have polarisation along the optical axis when they are passed through it and are absorbed. The other types of lights are transmitted as they are perpendicular to the axis. The device which polarises the light is known as polarizer.