Explanation of transverse nature of light:
i. Consider a tourmaline crystal C1 with its crystallographic axis perpendicular to the direction of propagation of light.
ii. Ordinary light (unpolarised light) is made incident on crystal C1 as shown in figure (a).
iii. The components of electric field vector which are in the plane of paper pass through the crystal and the components of electric field vector which are perpendicular to the plane of paper are blocked.
iv. Light transmitted through the crystal C1 has only one component of electric vector. Thus, crystal C1 has restricted the vibration of light in one direction. Thus light is polarised by crystal C1. Hence C1 is called polariser and the light transmitted by it is called linearly polarised light.
v. Now, another tourmaline crystal C2 with its axis parallel to crystal C1 is placed in the path of linearly polarised light. In this case, polarised light is fully transmitted through crystal C2.
vi. When the crystal C2 is rotated with respect to crystal C1, the intensity of light transmitted by crystal C2 decreases.
vii. When axis of crystal C2 is perpendicular to crystal C1, then no light is transmitted through the crystal C2 as shown in figure (b).
viii. From the above explanation, it is observed that there is restriction of vibration of light in the plane of propagation, hence light is polarised.
ix. Crystal C1 polarised the ordinary light i.e., unpolarised light, so it is called polariser while crystal C2 detects the polarising nature of light hence it is called analyser or detector.
x. Since polarisation takes place only in case of transverse waves, hence light is a transverse wave.
