Wave Motion, Properties, and the Doppler Effect

Comprehensive vocabulary flashcards covering wave fundamentals, wave phenomena (reflection, refraction, diffraction, interference, polarisation), stationary waves, and Doppler effect applications.

Wave

A means of transferring energy from one place to another.

Mechanical waves

Waves that must have a substance (medium) to travel through, consisting of vibrations travelling from one molecule to another.

Electromagnetic waves

Waves that travel through a vacuum at the speed of light.

Travelling wave

A disturbance which travels out from the source producing it, transferring energy from the source to other places through which it passes.

Periodic travelling wave

A continuous series of travelling waves with even spacings, such as waves travelling out as concentric circles when stones are dropped into water at even intervals.

Amplitude ($A$)

The maximum displacement from equilibrium.

Wavelength ($\lambda$)

The distance from a point on one cycle to the same point on the next cycle.

Frequency ($f$)

The number of complete cycles per second, measured in hertz ($\text{Hz}$).

Wave energy relationship

The mathematical relationship stating that the energy carried by a wave is proportional to the square of its amplitude ($E \propto A^2$).

Transverse waves

Waves where the direction of vibration is perpendicular to the direction in which the wave travels, propagating as a series of crests and troughs.

Longitudinal waves

Waves where the direction of vibration is parallel to the direction in which the wave travels, propagating as a series of compressions and rarefactions.

Wave equation

The equation $c = f\lambda$, where $c$ is the speed of the wave, $f$ is the frequency, and $\lambda$ is the wavelength.

Reflection

The bouncing of a wave off an obstacle.

Refraction

The changing of direction of a wave when it goes from one medium to another, caused by a change in speed as it enters a medium of different density.

Diffraction

The spreading out of waves into a region beyond an obstacle, which is only noticeable when the width of the gap is comparable with the wavelength of the wave.

Interference

The interaction occurring when two waves meet to produce a new wave whose size at any point is the algebraic sum of the two original wavefronts.

Constructive interference

Interference where the amplitude of the resulting wave is greater than the original waves; total constructive interference occurs when crest meets crest and trough meets trough.

Destructive interference

Interference where the resulting wave has an amplitude smaller than the original waves; total destructive interference occurs when crest meets trough and the effects cancel out.

Coherent waves

Waves produced by two sources that are in phase (giving out waves at the same rate and at the same time) or maintain a constant phase difference between them.

Interference pattern

The resulting wave pattern formed when two waves from coherent sources meet.

Antinodal lines

The lines of maximum disturbance in an interference pattern.

Nodal lines

The lines of minimum disturbance (calm areas in the case of water waves) in an interference pattern.

Polarisation

The process of filtering wave vibrations so they occur in only one plane; it only occurs for transverse waves and serves as a test to distinguish transverse waves from longitudinal waves.

Polaroid

A piece of transparent material composed of long molecules aligned next to each other, creating a series of tiny parallel slits that only transmit vibrations in that plane.

Stationary waves

Waves formed when two periodic waves of the same frequency and amplitude travelling in opposite directions meet, producing fixed points of rest (nodes) and points of maximum displacement (antinodes).

Nodes

Points along a stationary wave that remain completely at rest, separated from adjacent nodes by a distance of $\frac{\lambda}{2}$.

Antinodes

Points along a stationary wave showing maximum displacement, separated from adjacent antinodes by $\frac{\lambda}{2}$ and from the next node by $\frac{\lambda}{4}$.

Doppler effect

The apparent change in the frequency of waves due to the relative motion between the source of the waves and the observer.

Observed frequency (source approaching)

The apparent frequency detected when a wave source moves toward an observer, calculated as $f' = \frac{f c}{c - u}$, where $f$ is source frequency, $c$ is wave speed, and $u$ is source speed.

Observed frequency (source receding)

The apparent frequency detected when a wave source moves away from an observer, calculated as $f' = \frac{f c}{c + u}$, where $f$ is source frequency, $c$ is wave speed, and $u$ is source speed.

Speed traps

A technological application where a speed gun emits microwaves that reflect off a moving vehicle with a Doppler-shifted wavelength and frequency to calculate the vehicle's speed.

Red shift

The phenomenon where the wavelength of light emitted from a star moving away from an observer appears longer, shifting toward the red end of the spectrum.

Doppler ultrasound

A medical imaging technique that uses sound waves to assess blood flow velocity and direction by detecting frequency shifts in echoes returning from moving red blood cells.