Introduction:
Polarisation refers to the orientation of the electric field vector associated with an electromagnetic wave. It is a fundamental property of light and plays an important role in many applications in optics and electronics.

Is polarisation a vector quantity?
Yes, polarisation is a vector quantity. This means that it has both magnitude and direction. The direction of the polarisation vector is perpendicular to the direction of propagation of the electromagnetic wave. The magnitude of the vector represents the amplitude of the electric field in that direction.

Explanation:
To understand why polarisation is a vector quantity, we need to understand the nature of electromagnetic waves. Electromagnetic waves are transverse waves, which means that the oscillations are perpendicular to the direction of propagation. In the case of light, the oscillations are in the electric and magnetic fields.

When an electromagnetic wave is polarised, it means that the electric field vector has a particular orientation. This orientation can be horizontal, vertical, or at any angle in between. The direction of the polarisation vector is always perpendicular to the direction of propagation of the wave.

The polarisation vector is a vector quantity because it has both magnitude and direction. The magnitude of the vector represents the amplitude of the electric field in the direction of polarisation. The direction of the vector represents the orientation of the electric field.

Conclusion:
In conclusion, polarisation is a vector quantity. It has both magnitude and direction, and the direction is perpendicular to the direction of propagation of the electromagnetic wave. Understanding polarisation is essential in many applications in optics and electronics, such as polarisation filters, liquid crystal displays, and optical communication systems.