Question

Explain the meaning of polarisation of light and show the difference between polarised and unpolarised light with the help of a suitable diagram.

Hint:

Use $n_i \propto e^{-E_g/(2k_BT)}$. As $T\downarrow 0$, $n_i\!\downarrow 0 $\Rightarrow$ \sigma=q(n\mu_n+p\mu_p)\!\downarrow 0$. Only at $T>0$ do intrinsic semiconductors conduct via thermally generated $e^-$–hole pairs.

Answer 1

Step 1: Definition of Polarisation of Light.
Polarisation of light refers to the orientation of the oscillations of the electric field vector in a particular direction. For natural or unpolarised light, the electric field oscillates in many directions perpendicular to the direction of propagation. However, when light is polarised, its electric field vibrates in a single direction.

Step 2: Mechanism of Polarisation.
- Polarised light is typically obtained from unpolarised light by passing it through a polarising filter or using other methods like reflection, refraction, or scattering.
- The electric field of polarised light oscillates only in one plane (or direction). This can be demonstrated using a Polaroid filter.

Step 3: Diagram showing Polarised and Unpolarised Light.

Step 4: Explanation of Diagram.
- Unpolarised light: The electric field oscillates in all directions perpendicular to the direction of propagation. In the diagram, the electric field vector is randomly oriented in different directions.
- Polarised light: The electric field is oriented in a specific direction, as shown by the uniform vector direction in the diagram.

Final Answer: Polarisation is the process by which the oscillations of the electric field in light are restricted to one plane. The difference is that unpolarised light has electric field oscillations in multiple directions, whereas polarised light has oscillations in only one direction.