Introduction to Optics and Reflection

• Optics is the branch of physics studying light's behavior, properties, interactions with matter, and instruments that use or detect it.
• Optical phenomena such as rainbows, halos, and mirages are explained by optics.

Nature of Light

• Light exhibits wave-particle duality, acting as both a wave and a particle.
• As a wave, light is an electromagnetic wave, defined by wavelength (λ) and frequency (f), related by c = λf, where c is the speed of light in a vacuum.
• As a particle, light consists of photons, discrete energy packets; a photon's energy (E) is given by E = hf, with h as Planck's constant.

Reflection

• Reflection occurs when a wave changes direction at an interface between two media, returning to its origin medium.
• Specular reflection: light reflects from a smooth surface at a specific angle, following the law of reflection where the incident angle equals the reflection angle.
• Diffuse reflection: light reflects from a rough surface and scatters in multiple directions.

Refraction

• Refraction is the change in a wave's direction as it moves from one medium to another, due to a speed change.
• Snell's Law: n₁sin(θ₁) = n₂sin(θ₂), describes the relationship between incidence (θ₁) and refraction (θ₂) angles, and refractive indices of two media (n₁ and n₂).
• Refractive index (n) of a medium: the ratio of light speed in a vacuum (c) to its speed in the medium (v), expressed as n = c/v.

Lenses

• A lens is a transmissive optical device using refraction to focus or disperse a light beam.
• Convex (converging) lenses are thicker in the middle and converge light rays to a focal point.
• Concave (diverging) lenses are thinner in the middle and diverge light rays.
• The lensmaker's equation: 1/f = (n - 1)(1/R₁ - 1/R₂), relates a lens's focal length (f) to its refractive index (n), and surface radii of curvature (R₁ and R₂).
• Thin lens equation: 1/do + 1/di = 1/f, relates object distance (do), image distance (di), and focal length (f) of a lens.
• Lens magnification (M): the ratio of image height (hi) to object height (ho), expressed as M = hi/ho = -di/do.

Interference

• Interference is when two or more waves superpose, forming a resultant wave with greater, lower, or the same amplitude.
• Constructive interference: waves are in phase, resulting in increased amplitude.
• Destructive interference: waves are out of phase, resulting in decreased amplitude.
• Young's double-slit experiment: demonstrates light wave interference, creating alternating bright and dark fringes. Fringe spacing (Δy) is given by Δy = λL/d, where λ is light wavelength, L is the distance to the screen, and d is slit separation.

Diffraction

• Diffraction is the bending of waves around obstacles or through apertures.
• Single-slit diffraction: light passes through a narrow slit, creating bright and dark fringes. The angle (θ) to the first minimum is sin(θ) = λ/a, with λ as light wavelength and a as slit width.
• Diffraction gratings: optical components with a periodic structure that splits and diffracts light into beams traveling in different directions.

Polarization

• Polarization is a transverse wave property describing oscillation direction.
• Unpolarized light oscillates in all directions perpendicular to propagation.
• Polarized light oscillates in a single direction.
• Linear polarization: the electric field vector oscillates along a straight line.
• Circular polarization: the electric field vector rotates in a circle.
• Polarization methods: polarizing filters, reflection, and scattering.

Optical Instruments

• Optical instruments use lenses, mirrors, and other components to manipulate light for many purposes.
• Cameras use lenses to focus light onto a sensor or film to capture images.
• Telescopes use lenses or mirrors to collect and focus light from distant objects for magnified viewing.
• Microscopes use lenses to magnify small objects, making them visible.
• The human eye: a natural optical instrument focusing light onto the retina, enabling sight.

Fiber Optics

• Fiber optics transmits light through thin, flexible glass or plastic fibers.
• Total internal reflection confines light within the fiber due to the refractive index difference between core and cladding.
• Fiber optics applications: telecommunications, medical imaging, and industrial sensing.

Holography

• Holography records and reconstructs a three-dimensional image of an object.
• Holograms are created by interfering a reference beam with light reflected from the object.
• Hologram illumination with a laser beam diffracts light, reconstructing the original object wave to create a 3D image.

Lasers

• A laser emits light through optical amplification via stimulated emission of electromagnetic radiation.
• Laser light is coherent, monochromatic, and collimated, making it useful for various applications.
• Lasers are used in laser pointers, CD players, barcode scanners, laser surgery, and laser cutting.