Light and Wave Phenomena

Types of Waves

Mechanical Waves

These waves require a material medium for transmission. There are two main types:

• Longitudinal Waves: These waves travel parallel to the direction of propagation.
• Transverse Waves: These waves travel perpendicular to the direction of propagation, such as the waves on a vibrating guitar string.

Electromagnetic Waves

These waves do not require a physical medium for transmission.

Examples of Waves:

• Sound Waves: Acoustic waves.
• Seismic Waves: Caused by Earth's activity.
• Electromagnetic Waves: Related to electromagnetic forces.
• Wave Power: Generated by wind.
• Mechanical Waves: Produced by mechanical energy.
• Radio Waves: Propagate through the air.

Reflection of Light

The incident ray, the normal, and the reflected ray all lie in the same plane. The angle of incidence equals the angle of reflection.

Reflection occurs when a light ray encounters a surface and changes direction, returning to the original medium. With a smooth surface like a mirror, the rays are reflected in a single direction. Any surface that reflects light rays is called a mirror. The light ray hitting the mirror is called the incident ray, and the ray bouncing back is called the reflected ray. This is specular reflection.

If the surface is not smooth, the rays are reflected in different directions. This is called diffuse reflection.

Refraction of Light

Refraction is the change in direction of light as it passes from one medium to another with a different density. When light moves from one medium to another, its speed, wavelength, and direction of propagation change. For example, light refracts when it passes from air into water.

Real Images

A real image is formed directly by light rays. Examples include projected slides and images formed by a transparency projector, where light rays are emitted and form the image on a screen.

Snell's Law

Snell's Law describes the mathematical relationship between the angles of incidence and refraction:

n₁sinθ₁ = n₂sinθ₂

where n₁ is the refractive index of the first medium, θ₁ is the angle of incidence, n₂ is the refractive index of the second medium, and θ₂ is the angle of refraction.

Snell's Law can also be expressed in terms of the speed of light in different media:

sinθ₁ / sinθ₂ = v₁ / v₂

Photometry

Photometry is the science of measuring light, specifically the brightness perceived by the human eye. It studies the ability of electromagnetic radiation to stimulate the visual system.

Formulas

• v = λ / T
• v = λf
• T = 1 / f