Understanding Light: Wave-Particle Duality

• Light is electromagnetic radiation visible to the human eye.

Nature of Light

• Light exhibits wave-particle duality, showing properties of both waves and particles.
• As a wave, light's characteristics are wavelength (λ), frequency (ν), and speed (c).
• The speed of light in a vacuum is about 299,792,458 meters per second.
• Wavelength and frequency relate inversely, described by c = λν.
• Light as a particle consists of photons, discrete energy packets.
• Photon energy (E) is proportional to its frequency, represented by E = hν, where h is Planck's constant.

Electromagnetic Spectrum

• Light is part of the electromagnetic spectrum, which includes a broad range of radiation types.
• The electromagnetic spectrum consists of radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays.
• These radiations vary in wavelength and frequency, with visible light being a small portion.
• Visible light wavelengths range from 380 nm (violet) to 750 nm (red).

Light-Matter Interaction

• Light interacts with matter through absorption, reflection, transmission, and refraction.
• Absorption happens when an atom or molecule absorbs a photon's energy, moving to a higher energy state.
• Reflection occurs when light bounces off a surface.
• Specular reflection is from smooth surfaces, where the incident and reflection angles are equal.
• Diffuse reflection comes from rough surfaces, scattering light in many directions.
• Transmission involves light passing through a material.
• Transparent materials allow light to pass through easily, while opaque ones do not.
• Refraction is when light bends as it enters a different medium, due to its speed changing.
• The extent of bending depends on the refractive indices of the materials, as described by Snell's law.

Color

• Color is how the human eye perceives different wavelengths of light.
• Cone cells in the eye are sensitive to red, green, and blue light.
• Combinations of these colors allow perception of many colors.
• Objects appear colored because they absorb and reflect certain light wavelengths.
• A red object, for example, reflects red light but absorbs most other wavelengths.
• Color can be described via models like RGB (red, green, blue) and CMYK (cyan, magenta, yellow, black).

Light Sources

• Light comes from natural and artificial sources.
• Natural light sources: the sun, stars, and lightning.
• Artificial light sources: incandescent bulbs, fluorescent lamps, and LEDs.
• Incandescent bulbs create light by heating a filament until it glows.
• Fluorescent lamps produce light by passing electricity through a gas, exciting phosphors.
• LEDs (light-emitting diodes) emit light through electroluminescence when electrons move through a semiconductor.

Properties of Light

• Light travels in straight lines.
• Lenses and mirrors can focus light.
• Light can be polarized, meaning its electric field oscillates in a specific direction.
• Polarizing filters can produce polarized light.
• Light can be diffracted, bending around obstacles or through narrow openings.
• Diffraction is more noticeable when the obstacle or opening is similar in size to the light's wavelength.
• Light can interfere with itself, creating constructive and destructive interference patterns.

Applications of Light

• Light has many applications across different fields.
• Vision: enables sight and perception.
• Photography: captures images using cameras and sensors.
• Communication: fiber optics use light for long-distance data transmission.
• Medicine: lasers are used in surgery, diagnostics, and therapy.
• Energy: solar cells convert light into electricity.
• Astronomy: telescopes gather light to study distant objects.
• Industry: lasers are used for cutting, welding, and material processing.
• Displays: LCD and LED screens use light to create images and text.