What determines the direction of wave polarisation?

The direction of wave polarisation is determined by the orientation of the electric field vector.

In more detail, wave polarisation refers to the orientation of the oscillations in a wave, particularly electromagnetic waves such as light. For electromagnetic waves, the oscillations occur in the electric and magnetic fields that constitute the wave. The direction of polarisation is specifically determined by the direction of the electric field vector, which is perpendicular to the direction of wave propagation.

To understand this, imagine a wave travelling along a straight line. The electric field vector could be oscillating up and down, left and right, or at any angle in between. This orientation of the electric field vector is what we refer to as the polarisation of the wave.

In unpolarised light, the electric field vectors are oriented in all possible directions perpendicular to the direction of propagation. However, when light is polarised, the electric field vectors all align in one specific direction. This can occur naturally, for example when light reflects off a surface, or it can be induced artificially using a polarising filter.

Polarisation is a crucial concept in many areas of physics and engineering. For example, it is used in the design of sunglasses and 3D glasses, in the transmission of radio signals, and in the study of light from distant stars and galaxies. Understanding the direction of wave polarisation can therefore provide valuable insights into the properties of light and other electromagnetic waves.