Understanding Light: Properties and Behavior

What is Light?

• Light from the Sun is vital for life on Earth.
• The Sun, a star, is approximately 1.50 x 10^8 km from Earth, which is substantially farther than the Moon.
• Nuclear reactions in the Sun generate light energy that is emitted in all directions.
• Despite Earth capturing only a small fraction of this light, it's sufficient to power photosynthesis and heat the planet.
• Light travels in straight lines; evidence includes beams of light in dusty air and sharp shadows.
• Light travels at an extremely high speed, capable of circling Earth's equator 7.5 times in a single second.

Light - An Electromagnetic Wave

• Heat energy is transferred through conduction and convection, requiring a medium (physical substance).
• Light, unlike heat, doesn't require a medium and travels through the vacuum of space using radiation.
• Thomas Young demonstrated light's wave-like properties in 1801.
• James Clerk Maxwell theorized in 1864 that electricity and magnetism are coupled, forming an electromagnetic wave that travels at the speed of light without needing a medium.
• Heinrich Hertz confirmed Maxwell's prediction in 1887 by discovering radio waves, and Wilhelm Konrad Roentgen discovered X-rays in 1895.

Electromagnetic Waves

• Electromagnetic waves include radio waves, X-rays, microwaves, radar, and ultraviolet light.
• Visible light is electromagnetic waves detectable by the human eye.
• The electromagnetic spectrum categorizes waves by energy levels.

The Visible Spectrum

• Isaac Newton demonstrated in 1666 that a triangular prism can slow and separate white light into different colors.
• Red light slows the least, while violet light slows the most, enabling the prism to separate the colors.
• Newton identified seven colors in white light and named them the spectrum.
• Infrared light, discovered by William Herschel in 1800, exists beyond the red light region and has a higher temperature.
• X-rays allow us to see a completely different picture of the galaxy
• Mnemonic ROY G. BIV can be used to remember the order of colors in white light (Red, Orange, Yellow, Green, Blue, Indigo, and Violet).

Electromagnetic Waves in Our Society

• Radio waves are used for AM/FM radio, TV signals, cellphone communication, radar, and astronomy.
• Microwaves are used for telecommunications, microwave ovens, and astronomy.
• Infrared light is used in remote controls, lasers, heat detection, and astronomy.
• Visible light is used for human vision, theatre lighting, rainbows, and optical telescopes.
• Ultraviolet light is used for tanning, vitamin D production, sterilization, and astronomy.
• X-rays are used for medical imaging, security equipment, cancer treatment, and astronomy.
• Gamma rays are used in cancer treatment and astronomy, and are a product of some nuclear decay.

How is Light Produced?

• Luminous objects produce their own light, while non-luminous object can only be seen when illuminated by the light shined on to them.
• The Sun is luminous whereas a tree is non-luminous.

Light From Incandescence

• Incandescence is the production of light due to high temperature.
• As an object heats up, it starts to glow, changing color from red to orange, yellow, white, and bluish-white.
• Incandescent light bulbs use a thin tungsten filament that glows when electricity passes through it.
• Only 5% to 10% of the electricity is converted into visible light, making them inefficient.
• Thomas Edison is credited with producing the first commercially useful incandescent light bulb.

Light from Electric Discharge

• Electric discharge occurs when an electric current passes through a gas, causing it to glow.
• Neon signs use this process with different gases resulting in different colors.
• The development of electric discharge in gas tubes comes from the invention in 1855 of a powerful vacumm pump by German Physicist Heinrich Geissler

Phosphorescence and Fluorescence

• Phosphorescence is the process where materials absorb light energy (mainly ultraviolet) and release visible light slowly, resulting in a glow-in-the-dark effect.
• Fluorescence occurs when a material absorbs ultraviolet light and immediately emits visible light.
• Fluorescent lights use both electric discharge and fluorescence, containing mercury vapor that emits ultraviolet light when excited, which then strikes the fluorescent coating on the tube to produce visible light.

Improving Lighting Efficiency

• Compact Fluorescent lights (CFLs) are four to five times more energy efficient than incandescent bulbs and are recommended for home and business use.
• CFLs are more expensive to purchase but are less expensive to operate, contain mercury, and should be taken to appropriate recycling centers.
• Chemiluminescence is the production of light from a chemical reaction with minimal heat production.
• Light sticks have two chemicals in one container until bent, after which they mix causing the light to be produced

Light From Bioluminescence

• Bioluminescence is light produced by living organisms.
• Glow-worms create light with chemical reactions including oxygen, luciferin, luciferase, and ATP creating visible light.
• Organisms use bioluminescence for protection from predators, to lure prey, or to attract mates.

Other Forms of Light Production

• Triboluminescence is the production of light from scratching, crushing or rubbing certain crystals.
• Light-emitting diodes (LEDs) are electronic devices using semiconductors to produce light when electric current flows in one direction.
• LEDs don't need a filament, do not produce heat, and are more energy efficient.
• LEDs used for indicator lights later led to the invention of Christmas lights, illuminated signs, and traffic lights.

Lasers

• Lasers emit light with unique properties: same energy level, pure color, intense and narrow beam.
• Laser is an acronym for Light Amplification by Stimulated Emission of Radiation.
• Research includes helium-neon lasers, other types of lasers, and applications like vision correction.

The Ray Model of Light

• The ray model uses straight lines to represent light's path, explaining reflection and refraction; lasers serve as evidence that light travels in a straight line.
• Geometric optics uses the concept of light rays to study how light interacts with objects.
• Transparent objects allow light to pass through clearly; translucent transmit some, but do not allow clear vision; opaque materials block light.

Reflection of Light

• Mirrors are polished surfaces exhibiting reflection, used for checking appearance.
• Mirror production started the 12th and 13th centuries, replacing metal plates. The back part of the mirror has a shiny thin film and the front has a glass portion to protect the thin film.
• Plane (flat) mirrors illustrate predictable light paths: the incident ray strikes the mirror, creating a reflected ray. A normal is perpendicular to the mirror surface and the angle of incidence equals the angle of reflection.
• Geometric optics uses light rays to determine how light interacts with objects.

Specular vs Diffuse Reflection

• Specular reflection is a reflection of light off a smooth, shiny surface
• Diffuse Reflection causes the reflection of light off an irregular or dull surface.

Images in Plane Mirrors

• A virtual image is formed, when your brain projects these light rays backwards in a straight line.
• Observation 1: The distance from the object to the mirror is exactly the same as the distance from the image to the mirror.
• Observation 2: The object-image line is perpendicular to the mirror surface.
• Acronym SALT is used to remember these four objects of an image in a plane mirror (Size, Attitude, Location, and type)

Curved Mirrors

• Curved mirrors are parts of a sphere.
• Concave mirrors have inner reflective surfaces; convex mirrors are outer ones.

Terminology of Concave Mirrors

• Centre of curvature of a mirror is at center, part of sphere forms curves mirror. Labelled as C.
• Principal axis of the mirror is the line going through center of curvature and center of the mirror.
• Use similar terms to describe each type of line concave and convex mirrors.

Refraction of Light

• Any light rays that are parallel to the principal axis will be reflected off the mirror through a ingle point.
• It labeled the focus F, where the parallel light rays some together is,