Polarisation of Light

Unpolarised and Polarised Light

Concept: Unpolarised light consists of light waves vibrating in all possible directions, while polarised light consists of light waves vibrating in a single direction or a preferred direction.

Mnemonic: Remember “UP UP” for “UNpolarised” and “PP” for “Polarised”.

Plane of Polarisation

Concept: The plane of polarisation is the plane containing the electric field vector of a polarised light wave.

Mnemonic: Imagine a “plane” cutting through the wave, like a “pizza slice”, and the electric field vector is contained within this plane.

Polaroids

Concept: Polaroids are devices made of a special material (usually a plastic sheet containing aligned molecules) that selectively transmits or blocks light waves based on their polarisation.

Mnemonic: Remember “P” for “P"olaroids and think of them as “passports” that control the “flow” of light waves based on their polarisation.

Brewster’s Law

Concept: Brewster’s law states that when unpolarised light is incident on a dielectric surface at a particular angle (known as the Brewster angle), the reflected light becomes completely polarised.

Mnemonic: Think of the “B” in Brewster’s law as “bounce” and remember that only the reflected light is polarised, not the transmitted light.

Double Refraction

Concept: Double refraction is a phenomenon where a light wave passing through certain materials (like calcite) splits into two rays with different polarisations.

Mnemonic: Imagine a light wave like a “double-decker bus” that splits into two “separate buses” inside the material, each with its own polarisation.

Nicol Prism

Concept: A Nicol prism is a device made of calcite that utilises double refraction to produce polarised light.

Mnemonic: Remember “Nicol” as “Nick o’ Light” because it “picks” out a specific polarisation of light.

Quarter-Wave Plate

Concept: A quarter-wave plate is a device that converts linearly polarised light into circularly polarised light or vice versa.

Mnemonic: Think of “Quarter-Wave” as a “quarter-turn” and remember that it changes the polarisation by 90 degrees.

Half-Wave Plate

Concept: A half-wave plate is a device that converts linearly polarised light into linearly polarised light with a 90-degree rotation of its plane of polarisation.

Mnemonic: Think of “Half-Wave” as a “half-turn” and remember that it rotates the polarisation by 180 degrees.

Optical Activity

Concept: Optical activity refers to the ability of certain substances (like sugar solutions) to rotate the plane of polarisation of light passing through them.

Mnemonic: Remember “OA” for “OPtical Activity” and imagine the light as an “arrow” being rotated by the substance.

Specific Rotation

Concept: Specific rotation is a measure of the extent to which a substance rotates the plane of polarisation of light.

Mnemonic: Think of specific rotation as the “fingerprint” of a substance regarding its optical activity.

Polarimetry

Concept: Polarimetry is a technique used to measure the polarisation properties of light, including the determination of specific rotation.

Mnemonic: Remember “Polarimetry” as “Polarisation Measurement”.

Applications of Polarisation

Concept: Polarisation of light has numerous applications, such as sunglasses, 3D glasses, liquid crystal displays (LCDs), stress analysis, and microscopy.

Mnemonic: Think of “P” for “P"olarisation and its “Power” in various applications.