Lesson 18 Electromagnetic Waves

Vocabulary flashcards covering key EM wave concepts, terms, and phenomena from the lecture notes.

Electromagnetic waves

Transverse waves consisting of oscillating electric and magnetic fields that propagate through space at the speed of light in vacuum; do not require a medium; also known as Hertzian waves.

Hertzian waves

Another name for electromagnetic waves, named after Heinrich Hertz who demonstrated their existence.

Transverse wave

A wave in which the oscillations are perpendicular to the direction of travel; EM waves are transverse.

Electric field

The electric component of an EM wave, representing the force per unit charge; oscillates perpendicular to the direction of travel.

Magnetic field

The magnetic component of an EM wave, perpendicular to both the electric field and the direction of travel.

Speed of light

The constant speed at which EM waves travel in vacuum, approximately 3 × 10^8 m/s.

Vacuum

Space devoid of matter through which EM waves can propagate without a medium.

Wavelength

The distance between adjacent crests (or troughs) of a wave.

Frequency

The number of wave cycles passing a fixed point per second; unit is hertz (Hz).

Amplitude

The maximum displacement of particles in the medium due to the wave; relates to the energy carried by the wave.

Energy of EM waves

Energy increases with higher frequency and higher amplitude; longer wavelength generally means less energy.

James Clerk Maxwell

Physicist who formulated the electromagnetic theory and predicted EM waves; showed changing electric and magnetic fields sustain EM waves.

Maxwellian (Hertzian) waves

EM waves predicted by Maxwell and experimentally verified; sometimes called Hertzian waves.

Radio waves

Electromagnetic waves with the longest wavelength and lowest frequency in the EM spectrum; used for broadcasting and communications.

Microwave

EM waves with wavelengths shorter than radio waves; used in radar, satellite links, Wi‑Fi, and cooking.

Infrared

EM waves between microwaves and visible light; not visible but felt as heat; used in heat sensing and remotes.

Visible light

Portion of the spectrum visible to the human eye; consists of ROYGBIV colors and forms white light when combined.

Ultraviolet

EM waves with wavelengths shorter than visible light; UVA, UVB, and UVC bands; can cause skin damage and DNA effects.

X-rays

High-energy, ionizing EM waves used in medical imaging and therapy; bones absorb X-rays, appearing white on radiographs.

Gamma rays

Highest-energy EM waves with the shortest wavelength; produced by radioactive decay and energetic processes; used in sterilization and cancer treatment.

Non-ionizing radiation

Radiation whose energy is not sufficient to ionize atoms; includes radio, microwave, infrared, visible, and much of UV.

Ionizing radiation

Radiation energetic enough to remove electrons from atoms; includes X-rays and gamma rays, capable of causing cellular damage.

Background radiation

Natural radiation present on Earth from cosmic rays, rocks, soil, water, and the human body; varies by location.

Potassium-40

A naturally occurring radioactive isotope found in foods (e.g., bananas) that contributes to background radiation.

Roy G. Biv.

Mnemonic for the colors of visible light in order: Red, Orange, Yellow, Green, Blue, Indigo, Violet.

Prism

A transparent optical element that disperses white light into its constituent colors (spectrum).

Spectral signatures

Variation of reflectance or emittance of a material with wavelength; used to identify substances.

Spectrum order

Sequence of EM waves by wavelength/frequency from gamma rays to radio waves.

Wavelength–frequency relation

c = fλ; in vacuum, the speed c equals the product of frequency and wavelength.

Antenna

Device that radiates or receives electromagnetic waves in a radio system.

Transmitter

Device that generates and sends electrical signals converted into EM waves.

Receiver

Device that detects EM waves and converts them back into electrical signals.

Ground waves

Radio wave propagation that travels along the Earth's surface, typical for low frequencies.

Sky waves

Radio waves that reflect off the ionosphere and return to Earth, enabling long-distance reception.

Space waves

Radio waves that travel through space, used for satellite communications and deep-space transmissions.

Visible light applications

Allows sight, supports photosynthesis, enables photography and color-based analyses.

Prism and white light

A prism disperses white light into a spectrum of colors; ROYGBIV represents that spectrum.