Waves, Radiation, and the Electromagnetic Spectrum (Vocabulary Flashcards)

A set of vocabulary flashcards covering gravity, planetary concepts, electromagnetic radiation, the electromagnetic spectrum, wave physics, and astronomical Doppler effects as presented in the lecture notes.

Gravitational force

The attraction between two masses; follows the inverse-square law (F ∝ 1/r^2); F = G m1 m2 / r^2.

Inverse-square law

A rule where a quantity decreases with the square of the distance from the source; gravity and many forces follow this law.

Newton's law of universal gravitation

Gravitational force between two masses given by F = G m1 m2 / r^2.

Terrestrial planet

Rocky, solid planets close to the Sun (e.g., Mercury, Venus, Earth, Mars).

Gas giant

Large planets dominated by hydrogen and helium with thick atmospheres (e.g., Jupiter, Saturn).

Inner planets

Planets closer to the Sun (Mercury, Venus, Earth, Mars).

Outer planets

Planets farther from the Sun (Jupiter, Saturn, Uranus, Neptune).

Radiation

Emission or transmission of energy through space as electromagnetic waves or particles.

Electromagnetic radiation

Energy that travels as oscillating electric and magnetic fields, at the speed of light, produced when charges accelerate.

Wavelength

Distance between successive crests (λ).

Frequency

Number of wave crests passing a point per second; unit is Hertz (Hz).

Period

Time for one complete wave cycle; P = 1/f.

Amplitude

Maximum displacement of a wave from its undisturbed state.

Crest

The top of a wave.

Trough

The bottom of a wave.

Wave velocity

Speed at which a wave crest travels; v = f λ.

Speed of light

In vacuum, c ≈ 3.0 × 10^8 m/s (about 300,000 km/s).

Electromagnetic spectrum

All wavelengths/frequencies of electromagnetic radiation, from radio to gamma rays; all are light.

Radio waves

Low-frequency, long-wavelength portion of the spectrum used for broadcasting and communications.

Microwaves

Wavelengths roughly from about 1 mm to 30 cm; used in microwave ovens and radar.

Infrared

Wavelengths just longer than visible light; associated with heat.

Visible light

Wavelengths visible to the human eye, roughly 400–700 nm.

Ultraviolet

Higher-energy, shorter-wavelength light than visible; can cause sunburn; used in sterilization; black lights.

X-rays

High-energy, short-wavelength radiation used in medical imaging and astronomy.

Gamma rays

Highest-energy electromagnetic radiation; produced in nuclear reactions and cosmic sources.

Doppler effect

Change in observed wavelength/frequency due to relative motion between source and observer.

Blue shift

Wavelengths shortened when the source moves toward the observer.

Red shift

Wavelengths lengthened when the source moves away from the observer.

Kelvin temperature scale

Absolute temperature scale used by scientists; 0 K is absolute zero; water freezes at 273 K and boils at 373 K.

Absolute zero

0 K, the lowest possible temperature where molecular motion ceases (theoretically).

Blackbody radiation

Radiation emitted by an idealized object depending only on its temperature.

Wien's Law

Peak wavelength of emission is inversely proportional to temperature; hotter objects peak at shorter wavelengths.

Stefan-Boltzmann Law

Total energy emitted per unit area is proportional to the fourth power of temperature (E ∝ T^4).

Planck's constant

Constant h relating a photon's energy to its frequency: E = h f.

Photon

A quantum of electromagnetic radiation; energy E = h f.

Light-minute

Distance light travels in one minute; used to express astronomical distances (e.g., Sun–Earth is about 8.3 light-minutes).

Look-back time

The concept that observing distant objects shows their state in the past due to the finite speed of light.

Atmospheric windows

Wavelength ranges where Earth's atmosphere is transparent to radiation (e.g., radio window, optical window).

Visible spectrum

The portion of the spectrum visible to humans, about 400–700 nm.

Hue order of visible colors

Colors from violet to red within the visible spectrum.

Frequency–wavelength relation (v = f λ)

Relation showing how frequency and wavelength determine wave speed in a medium or vacuum.

Energy–frequency relation (E = h f)

Photon energy is proportional to frequency via Planck's constant.

Wavelength units (nm, Å)

Nanometer (nm) and Angstrom (Å) are common units for light wavelengths: 1 nm = 10^-9 m; 1 Å = 10^-10 m.

Undisturbed state

Equilibrium position of a medium before a wave passes.

Frequency (Hz) vs. wavelength (m) scale

Low frequencies correspond to long wavelengths; high frequencies to short wavelengths across the spectrum.

Doppler velocity in exoplanet studies

Using observed Doppler shifts to infer the speed of stars due to orbiting planets.