Sound Waves and Wave Motion

Comprehensive flashcards covering the concepts of wave motion, oscillatory characteristics, mechanical and electromagnetic waves, and the phenomena of reflection, resonance, and audibility limits.

Amplitude ($a$)

The magnitude of maximum displacement to one side from its equilibrium position; its SI unit is the metre ($m$).

Oscillation

The movement completed when a body returns to its initial position in the same direction from where it started, such as a pendulum moving from point O to both sides and back to O.

Invar

An alloy used in early pendulum clocks to make a seconds pendulum of length $99.35\,cm$ because it is invariable.

Period ($T$)

The time taken for one oscillation; its SI unit is the second ($s$).

Frequency ($f$)

The number of oscillations in one second; its SI unit is the hertz ($Hz$).

Heinrich Rudolf Hertz

The German scientist who experimentally proved the presence of electromagnetic waves and discovered the photoelectric effect.

Kilohertz ($kHz$)

A practical unit of frequency equivalent to $1000\,Hz$ or $10^{3}\,Hz$.

Megahertz ($MHz$)

A practical unit of frequency equivalent to $1000000\,Hz$ or $10^{6}\,Hz$.

Natural Frequency

The innate frequency at which an object vibrates when it vibrates freely, influenced by length, size, elasticity, and nature of material.

Forced Vibration

The vibration of an object induced by an external vibrating object.

Resonance

A phenomenon that occurs if the frequency of the forcing object and the natural frequency of the forced object are equal, causing the objects to vibrate with maximum amplitude.

Wave Motion

One of the modes of transfer of energy from one part of the medium to other parts through continuous propagation of energy via oscillations.

Electromagnetic Waves

Waves that do not require a medium for transmission, such as radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays.

Mechanical Waves

Waves that require a medium for transmission, such as sound waves, water ripples, and seismic waves.

Longitudinal Waves

Waves in which the particles in the medium vibrate parallel to the direction of propagation of the wave.

Compressions ($C$)

Regions of high pressure in a longitudinal wave where the distance between the molecules decreases.

Rarefactions ($R$)

Regions of low pressure in a longitudinal wave.

Transverse Waves

Waves in which the particles of a medium vibrate perpendicular to the direction of propagation of the wave, such as electromagnetic waves.

Crests

The elevated portions from the equilibrium position in a transverse wave.

Troughs

The lowest portions from the equilibrium position in a transverse wave.

Wavelength ($\lambda$)

The distance between two consecutive particles which are in the same phase of vibration, such as the distance between two consecutive crests or two consecutive compressions.

Speed of Wave ($v$)

The distance travelled by the wave in one second, calculated as the product of frequency and wavelength ($v = f\lambda$).

Persistence of Hearing

The characteristic where the auditory experience produced by a sound persists for about $\frac{1}{10}$ of a second.

Echo

The sound heard after a while due to the reflection of the initial sound; requires a minimum reflecting surface distance of $17.5\,m$ in air.

Reverberation

The lingering of sound even after the original sound has ceased, caused by multiple reflections.

Infrasonic

Sound with a frequency below $20\,Hz$.

Ultrasonic

Sound with a frequency more than $20000\,Hz$.

Ultrasonography

A medical imaging technique where ultrasonic waves strike and reflect at areas of varying density in body tissues to form an image of an organ.

SONAR

A device used to find the distance to underwater objects by emitting ultrasonic waves.

Seismic Waves

Waves that travel through the Earth's crust as a result of earthquakes, volcanic eruptions, and massive explosions.

Seismology

The study of seismic waves.

Richter Scale

The scale used to determine the intensity of earthquakes.

Tsunami

A series of gigantic ocean waves caused by the displacement of large volumes of water in the sea, often triggered by earthquakes at the bottom of oceans.