3 - Waves (Sound & Light)

Wave

A disturbance that transfers energy through matter or space without transferring matter.

Mechanical waves

Waves that require a medium to transfer, such as sound and water.

Non-mechanical waves

Waves that do not require a medium to transfer, such as electromagnetic waves.

Wavelength (λ)

Length of 1 complete wave, measured in meters (m).

Frequency (f)

Number of waves passing a point per second, measured in Hertz (Hz).

Speed (v)

Distance travelled by a wave per unit time, measured in meters per second (m/s).

Time period (T)

Time taken for 1 complete wave, measured in seconds (s).

Crest (Peak)

The highest point of a wave.

Trough

The lowest point of a wave.

Amplitude

Displacement from an undisturbed point of a wave to a crest or trough.

Wavefront

Line or plane on which all particles vibrate in the same way (or same phase).

Transverse waves

Waves where particles vibrate perpendicular to the wave motion or direction of energy transfer.

Longitudinal waves

Waves where particles vibrate parallel to the direction of wave motion or energy transfer.

Refraction

Bending of a wave when it enters a different medium.

Diffraction

Bending of waves around an obstacle.

Pitch

The perceived frequency of a sound; higher frequency corresponds to higher pitch.

Loudness

The perceived intensity of a sound, directly proportional to amplitude.

Audible range

The range of frequencies that can be heard by the human ear, typically from 20 Hz to 20 kHz.

Real image

An image that can be obtained on a screen, formed when light rays meet.

Virtual image

An image that cannot be obtained on a screen, formed when light rays do not meet.

Total internal reflection

Complete reflection of light back into the original medium when going from a denser to a rarer medium.

Critical angle

The angle of incidence above which total internal reflection occurs.

Dispersion of light

The splitting of light into its component colors when passed through a prism.

Convex lens

A lens that converges light rays that are parallel to its principal axis.

Concave lens

A lens that diverges light rays that are parallel to its principal axis.

Refractive index (n)

A measure of how much the speed of light changes as it enters a medium; it is constant for a given medium.

Electromagnetic waves

Non-mechanical transverse waves traveling at the speed of light in a vacuum.

VIBGYOR

An acronym used to memorize the colors of the spectrum: Violet, Indigo, Blue, Green, Yellow, Orange, Red.

Sound speed in air

Approximately 330–350 meters per second.

Sound speed in water

Approximately 1500 meters per second.

Speed of light in vacuum

Approximately 3 x 10⁸ meters per second.

Echo

A reflection of sound arriving back after a delay.

Lateral inversion

The sideways reversal of images seen in plane mirrors.

Wave Speed Formula

v = f × λ

Frequency Formula

f = 1/T

Time Period Formula

T = 1/f

Refractive Index Formula

n = c/v

Speed of Sound Formula in Different Mediums

v = √(B/ρ)

Critical Angle Formula

sin(θc) = n2/n1