Optics Overview

Optics

• Optics is a branch of physics that studies light's behavior and properties, including its interactions with matter and the design of instruments that use or detect light.

Geometrical Optics vs. Physical Optics

• Geometrical optics deals with the reflection and refraction of light.
• Physical optics deals with interference, diffraction, and polarization of light.

Facts of Light

• Light is essential, and its absence would dramatically alter the world.
• Humans have developed various methods to produce and control light, including campfires, torches, candles, oil lamps, gas lights, and electric lights.

Wave Theory of Light

• The wave theory of light posits that light travels as waves.
• Christian Huygens explained wave fronts as perpendicular to the path of light rays.
• Wave theory suggests light originates from vibrating sources and travels at high speeds.

Corpuscular Theory of Light

• In 1704, Sir Isaac Newton countered the wave theory by proposing light travels as particles called corpuscles, also known as the emission theory.
• This theory states light particles emanate from a source and travel only in straight lines.

Speed of Light

• The speed of light is a crucial physical quantity, precisely measured in physics.
• Galileo Galilei initially hypothesized a finite speed of light, though it couldn't be proven in his time.
• Ole Roemer made the initial measurement of light's speed over astronomical distances.
• Albert A. Michelson refined the measurement, culminating in the accepted value of 2.9979 x 10⁸ m/s for the speed of light in a vacuum.

Sources of Light

• All light emanates from a source.
• Luminous objects generate their own light and often radiate heat.
• Non-luminous objects reflect light to be seen.

How Light is Produced

• Light production occurs via incandescence and luminescence.
• Incandescence is light produced from an object heated to a high temperature, such as a glowing object.
• Luminescence is light generation via processes other than heating.

Luminescence Types

• Fluorescence: Light release lasting less than 10 nanoseconds, exemplified by fluorescent bulbs.
• Phosphorescence: Light release longer than 10 nanoseconds, observed in glow-in-the-dark objects.

Light and Transparency

• Objects are categorized based on how light passes through them.
• Transparent objects allow all light to pass through. (e.g. air, glass)
• Translucent objects allow some light to pass through.
• Opaque objects do not allow light to pass through. (e.g. wood)

Shadows

• Opaque objects cast shadows, whose sharpness depends on the light source size.

Brightness of Light

• Photometry measures light illumination and brightness.
• Luminous intensity is light source brightness, measured in candelas (cd).
• Luminous flux is the luminous energy emitted, measured in lumens (lm).