Comprehensive Light Properties, Phenomena, and Applications for Physics Students

Light

Light is the source of energy that provides us with the sensation of seeing.

Luminous Objects

Objects that emit light, such as the Sun, flames, electric lamps, and lightning.

Non-luminous Objects

Objects that do not emit light.

Examples of Light Sources from Electric Discharge

Spark plugs, lightning, fluorescent lamps, mercury-vapor lamps, sodium-vapor lamps.

Main Properties of Light

Light travels in a straight line, is an electromagnetic wave, can travel through a vacuum, is a transverse wave, moves at 3×10⁸ m/s in vacuum, changes wavelength when moving between media, casts shadows when blocked, and is the fastest thing in the universe.

Seven Principles of Light

Reflection, refraction, diffraction, interference, polarization, dispersion, and scattering.

Five Basic Characteristics of Light

Travels in a straight line, is an electromagnetic wave, can travel in a vacuum, is a transverse wave, travels at 3×10⁸ m/s in vacuum.

Reflection of Light

The bouncing back of light from a surface.

First Law of Reflection

The angle of incidence is always equal to the angle of reflection (θᵢ = θᵣ).

Second Law of Reflection

The incident ray, reflected ray, and normal at the point of incidence all lie in the same plane.

Specular Reflection

Reflection from a smooth surface where reflected rays remain parallel (mirror-like).

Diffuse Reflection

Reflection from a rough surface that scatters light in many directions.

Refraction of Light

The bending of light when it passes from one medium to another due to change in speed.

Laws of Refraction

The incident ray, refracted ray, and normal all lie in the same plane. The ratio of sinθᵢ to sinθᵣ is constant (Snell's Law).

Snell's Law (concept)

States that n₁ sinθ₁ = n₂ sinθ₂, relating refractive indices and angles of incidence/refraction.

Index of Refraction

Ratio of the speed of light in vacuum to the speed of light in a medium (n = c/v, n ≥ 1).

Constant When Light Passes Between Media

Frequency (ƒ) stays constant; speed and wavelength change.

Dispersion of Light

Splitting of white light into component colors because refractive index depends on wavelength.

Example of Dispersion in Real Life

Prisms and rainbows.

Absorption of Light

When light energy is partially converted into heat in a medium, reducing intensity.

Polarization of Light

When light waves vibrate in only one plane perpendicular to the direction of travel (plane-polarized light).

Ways Light Can Become Polarized

Reflection from a surface or passing through a polarizing filter.

Formation of a Rainbow

Light refracts into a raindrop, reflects internally, then refracts out, producing a spectrum of colors (red ≈ 42°, violet ≈ 40°).

Critical Angle

The angle of incidence where the refracted ray travels along the boundary (θ₂ = 90°).

Total Internal Reflection (TIR)

When light travels from a denser medium to a rarer medium at an angle greater than the critical angle, it is completely reflected back into the denser medium.

Applications of Total Internal Reflection

Fiber optics (telecom, endoscopy) and sparkle of diamonds.

Contributions to Light Theory

Newton proposed particle theory; Huygens proposed wave theory; Young proved wave theory by interference; Maxwell showed light is an EM wave; Planck showed EM radiation is quantized; Einstein explained photoelectric effect (particle nature).

Photon

A quantum (particle) of light energy that has both wave and particle properties.

Formula for Energy of a Photon

E = hƒ, where h = 6.63 × 10⁻³⁴ J·s and ƒ = frequency.

Light Ray

An imaginary line that shows the direction of light travel, perpendicular to wavefronts.