Light Year, Magnetic Intensity, and Malus's Law

Many people think a 'Light Year' is a unit of time because it contains the word 'year'. This is incorrect.

• A Light Year is a unit of DISTANCE.
• Definition: It is the total distance that light travels in the vacuum of space in one Earth year.
• Value: Since light travels at an incredible speed of 3,00,000 km per second, one light-year is roughly equal to 9.46 Trillion Kilometers. It is used to measure the vast distances between stars and galaxies.

In magnetism, Magnetic Intensity (H) (also called Magnetic Field Strength) refers to the degree or extent to which an external magnetic field can magnetize a material.

• Formula: H = B/μ₀ - M (where B is the magnetic field, μ₀ is the permeability of free space, and M is magnetization).
• SI Unit: Its SI unit is Ampere per meter (A/m).

In the wave optics chapter (Class 12), Malus's Law explains what happens to the intensity of polarized light when it passes through a polarizing filter (analyzer).

• The Law: It states that the intensity of polarized light transmitted through an analyzer varies as the square of the cosine of the angle between the transmission axis of the analyzer and the polarizer.
• Formula: I = I₀ cos²θ (Where I is the final intensity, I₀ is the initial intensity, and θ is the angle).