PHY 1020 – Chapter 7: Waves, UFOs, Earthquakes, and Music

Vocabulary flashcards covering key terms and definitions from PHY 1020 Chapter 7 on waves, sound, earthquakes, and related phenomena.

Wave

A disturbance or oscillation that transfers energy through space or matter.

Amplitude (y)

The maximum displacement or density variation of a wave from its undisturbed position.

Wavelength (λ)

The spatial size of one complete wave cycle; distance between successive crests or compressions.

Period (T)

Time for one wavelength to pass a point; calculated by T = λ / v.

Frequency (f)

Number of wavelengths that pass a point per second; calculated by f = v / λ.

Longitudinal Wave

A wave in which particle displacement is parallel to the direction of propagation (e.g., sound).

Transverse Wave

A wave in which particle displacement is perpendicular to the direction of propagation (e.g., water surface ripples, light).

Superposition Principle

When two or more waves overlap, the resultant displacement equals the algebraic sum of their individual displacements.

Constructive Interference

Superposition that increases wave amplitude because crests coincide with crests (or compressions with compressions).

Destructive Interference

Superposition that decreases wave amplitude because crests coincide with troughs (or compressions with rarefactions).

Huygens Principle

The spreading of waves through an opening described by S = (λ R) / D, where S is spread, R distance, D opening size.

Pitch

The perceived highness or lowness of a sound; rises with increasing wave frequency.

Sound Wave

A compression (longitudinal) wave of molecules that vibrates the eardrum; speed increases with material stiffness.

Beats

Alternating loud and soft sound due to interference of two close frequencies; beat frequency f_B = |f2 – f1|.

Intensity (I)

Power per unit area carried by a wave, measured in W/m².

Decibel (dB)

Logarithmic unit of sound level: I[dB] = 10 log10(I / I₀) where I₀ = 1.0 × 10⁻¹² W/m² (threshold of hearing).

Threshold of Hearing

The minimum audible intensity for humans, approximately 1.0 × 10⁻¹² W/m² (0 dB).

Doppler Shift

Change in observed wave frequency due to relative motion between source and observer; higher on approach, lower on recession.

SOFAR Channel

A deep-ocean layer where sound speed is minimum, guiding low-frequency sound thousands of miles by refraction.

Primary (P) Wave

Longitudinal seismic wave that arrives first during an earthquake.

Secondary (S) Wave

Transverse seismic wave that arrives second during an earthquake.

Long (L) Wave

Surface seismic wave with both transverse and longitudinal motion; arrives last and often causes most damage.

Earthquake Magnitude (M)

Logarithmic measure related to wave amplitude and distance: M = log10(A / A₀(d)).

Shallow-Water Wave

Water wave occurring when wavelength > 20× water depth; strongly interacts with seafloor and speed ≈ √(g D).

Deep-Water Wave

Water wave where water depth > ½ wavelength; little interaction with seafloor.

Intermediate-Water Wave

Water wave in transition regime between shallow and deep, with partial seafloor interaction.

Tsunami

Long-wavelength, high-energy ocean wave typically generated by underwater earthquakes; can travel ~171 m/s (~386 mph).

Run-up Height

Maximum vertical height a tsunami wave reaches onshore above sea level.