Properties, Spectrum, and Behavior of Electromagnetic Waves in Physics

Electromagnetic Waves

Light is an electromagnetic wave (EM wave).

Generation of Light

Created by vibrating electric charges, which generate a vibrating magnetic field, which in turn regenerates the electric field.

Propagation of Light

Self-propagating, with oscillating electric and magnetic fields perpendicular to each other and to the direction of motion.

Speed of Light (c)

Constant speed: (c = 3 × 10^8) m/s. Does not require a medium to travel.

James Clerk Maxwell

Found that the speed of all electromagnetic waves was exactly the speed of light.

Einstein's Conclusion

The speed of light is the universal speed limit. No object with mass can reach (c).

Speed of Light in a Vacuum

The speed of light in a vacuum is constant for all observers, regardless of their motion.

Relative Speed of Light

An observer in a spaceship going 99% the speed of light would still see light traveling at (c).

Electromagnetic Spectrum

All EM waves are classified based on their frequency and wavelength.

Relationship of Speed, Frequency, and Wavelength

(c = fλ), where (c) is the speed of light, (f) is frequency, and (λ) is wavelength.

Inverse Relationship of Frequency and Wavelength

Since (c) is constant, frequency (f) and wavelength (λ) are inversely related.

Spectrum Components

Radio waves, Microwaves, Infrared, Visible Light (ROYGBIV), Ultraviolet (UV), X-rays, Gamma Rays.

Wavelength

Distance between two points on a wave.

Frequency

Number of wave cycles that pass a fixed point per second.

Reflection

Bouncing off surfaces (e.g., mirrors).

Absorption

Light energy converted into internal energy (heat) in a material.

Transmission

Light passes through a material.

Opaque Objects

Stops light transmission entirely (absorbs and/or reflects). Ex: A wall.

Translucent Objects

Allows light to transmit but scatters it, making images blurry. Ex: Frosted glass.

Transparent Objects

Allows light to transmit without scattering, so objects can be seen clearly. Ex: Clear window glass.

Shadows

A region where light rays are blocked.

Umbra

The central, darkest part of a shadow where all light from the source is blocked (total shadow).

Penumbra

The lighter, partial part of a shadow where some light reaches, but not all.

Solar Eclipse

Moon's shadow falls upon the Earth.

Lunar Eclipse

The Moon passes into the Earth's shadow.

Rods

Highly sensitive to dim light (low intensity) but cannot perceive color.

Cones

Require high-intensity light to fire and allow us to perceive color.

Color Blindness

Physical or inherited issues with cones.

Fermat's Principle of Least Time

Light takes the path that requires the least time, not necessarily the shortest distance.

Law of Reflection

(θ_i = θ_r) where θ_i is the angle of incidence and θ_r is the angle of reflected light.

Refraction

The bending of light as it travels through different media.

Index of Refraction (n)

A measure of how much the speed of light slows down in a particular medium.

Snell's Law of Refraction

Describes the amount of bending that occurs: (n_1 sin(θ_1) = n_2 sin(θ_2)).

Dispersion

Different wavelengths (colors) of light bend by different amounts.

Total Internal Reflection (TIR)

Occurs when light is completely reflected back into the original medium.

Critical Angle

The specific angle of incidence where the angle of refraction is (90°).

Fiber Optics

Uses TIR to allow light rays to travel long distances within a thin fiber.

Lens

A piece of transparent material that causes light to bend and either converge or diverge.

Biconcave Lens

Causes parallel light waves to diverge.

Biconvex Lens

Causes parallel light waves to bend inward and converge.

Focal Point

The point where the converging rays meet.

Virtual Image

Image that is upright and larger than the object when viewed through a biconvex lens between the focal point and the lens.

Real Image

Image that is inverted and magnified when the object is beyond the focal point.

Farsightedness (Hyperopia)

Condition where eyes focus light behind the retina, corrected with biconvex lenses.

Nearsightedness (Myopia)

Condition where eyes focus light in front of the retina, corrected with biconcave lenses.

Principle of Superposition

When two or more waves overlap, their amplitudes combine.

Constructive Interference

Occurs when waves are in phase, resulting in brighter light.

Destructive Interference

Occurs when waves are out of phase, resulting in dimmer or dark areas.

Evidence for Wave Nature

Interference patterns show that light behaves like a wave.

Huygens' Principle

Every point on a wavefront acts as a source of spherical waves.

Plane Wave Diffraction

A plane wave traveling through a narrow opening will curve at the edges.

Diffraction

The bending or spreading of waves as they pass through an opening or around a barrier.

Single-Slit Diffraction

Produces a central bright fringe with smaller fringes on either side.

Double-Slit Experiment

Combines diffraction and interference, producing a pattern of bright and dark bands.

Diffraction Grating

Consists of evenly spaced slits and produces sharp, well-separated bright bands for each wavelength.

Thin-Film Interference

Occurs when light reflects off the top and bottom surfaces of a thin layer.

Polarization

A property of transverse waves where the electric fields oscillate in only one direction.

Unpolarized Light

Electric fields oscillate in all directions perpendicular to motion.

Polarized Light

Electric fields oscillate in only one direction.

How to Polarize Light

A polarizing filter blocks all but one orientation of electric field oscillation.

Ground State

Lowest energy level of electrons in atoms.

Excited States

Higher energy levels of electrons in atoms.

Excitation

When an electron absorbs energy and jumps to a higher energy level.

De-excitation

When an electron falls back down and releases energy as light.

Photon Energy Formula

The energy of a photon is given by E = hf, where h is Planck's constant.

Emission Spectra

Each element has unique energy levels, producing a unique pattern of light when excited.

Absorption Spectra

Specific wavelengths absorbed when white light passes through a gas, appearing as dark lines.

Incandescence

Light emission due to high temperature, producing a continuous spectrum.

Fluorescence

Material absorbs high-frequency light and emits lower-frequency visible light.

Phosphorescence

Similar to fluorescence but with a time delay in light emission.