(a) Differentiate between plane polarization and interference as applied to waves. (b) List two uses of polaroids.

Answer Details

(a) Plane polarisation compared with interference

• Plane polarisation is the restriction of the vibrations of a transverse wave to a single plane (one direction) perpendicular to the direction of travel. It shows that light is a transverse wave and occurs only with transverse waves.
• Interference is the superposition of two waves of the same frequency travelling in the same region, producing points of reinforcement (constructive) and cancellation (destructive). It occurs with both transverse and longitudinal waves and demonstrates the wave nature of light.

In short, polarisation concerns the plane of vibration of a single wave, while interference concerns the combined effect of two coherent waves.

(b) Two uses of polaroids

• In sunglasses (polaroid spectacles) to reduce glare from reflected sunlight.
• In camera filters and in the control of light intensity, e.g. in liquid-crystal displays and photographic work.