• Waves are disturbances which originate from some vibrating source and propagate through a medium and vacuum.
• A medium is the substance through which a wave can propagate.
• A single non-repeating disturbance traveling in a medium is called a pulse.
• The maximum displacement of the wave from the equilibrium position is called the amplitude of the wave.
• The wavelength (λ) is the distance between any two adjacent points which are in phase.
• The period (T) is the time taken for a wave to make one complete vibration.
• The frequency of a wave, f , is a measure of how many complete oscillations occur, in one second.
• The speed of a wave refers to the distance travelled by a given point on the wave in a given interval of time

• Wave front is defined as the imaginary surface constructed by the locus of all points of a wave that have the same phase.
• The direction of travel of the wave fronts is shown by a straight line with an arrow called a ray.
• Reflection is turning back of a wave into the first medium when reaching to a boundary through which it can not pass
• The change in the direction of waves at the boundary between two different media is known as refraction.
• The change of direction of the wave fronts when they pass through a gap is called diffraction.
• The mixing up of two or more identical waves that travel in the same medium is called interference.
• The process of transforming unpolarized wave into polarized wave is known as polarization.
• Mechanical waves are waves that require a medium in order to transport their energy from one location to another.
• Electromagnetic waves are waves that do not require a material medium to transmit the disturbance.
• A transverse wave is a wave in which particles of the medium move in a direction perpendicular to the direction that the wave moves.
• A longitudinal wave is a wave in which particles of the medium move in a direction parallel to the direction that the wave moves.
• Standing waves are waves that do not appear to be propagating. They are also called stationary waves.
• The speed of sound in air depends on the temperature of the air, and is given by the equation:

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• The reflection of sound from an obstacle is called echo.
• Unpleasant sounds are called noise and sounds which are pleasant to hear are called music.
• The Loudness of a sound is the magnitude of the auditory sensation produced by the sound.
• The pitch of a sound is the subjective feeling experienced by a listener due to the frequency of the sound.
• Sound waves that are able to produce sensation of hearing are called audible, and those waves that cannot produce sensation are Inaudible.
• The amount of energy (E) transferred per unit time (t) per unit Area (A) perpendicular to the direction of motion is called the intensity (I) of the wave.

• The intensity of a sound wave is inversely proportional to the square of the distance of the point of measurement from the sound source. Ir² = constant
• The intensity of a sound wave is directly proportional to the square of the amplitude of vibration of the source, I α A².
• The intensity level of a sound, having intensity I, is given by:

• The change in the frequency of the sound heard by the listener due to the relative motion between the source and the listener is known as Doppler Effect
• The interference of two identical waves having the same frequency, wavelength and amplitude, which are traveling in opposite directions in the same medium gives rise to standing wave pattern.
• The special frequencies at which the standing waves are made are called the resonance frequencies.
• For a standing wave produced by a vibrating string:

and

• The speed of a wave in a Vibrating string:

• For a closed pipe:

• Beats are the periodic and repeating fluctuations heard in the intensity of a sound when two sound waves of very similar frequencies interfere with one another.
• The number of beats per second, called the beat frequency (f_b) is given by: f_b= | f₁- f₂ |