Waves - Optics - Sound

A wave is a rhythmic disturbance that transfers energy through space or matter.
 

A wave possesses kinetic energy of motion.
 

In transverse waves the top of wave form is called the crest (an antinode) while bottom is the trough (another antinode).  See drawings given in class.
 

Wavelength is the linear distance between any two corresponding points on consecutive waves.
 

The amplitude of a wave is the distance a wave rises or falls from its usual resting position. The amplitude of a wave is dependent on the energy that creates the wave.
 

The frequency of a wave refers to the number of waves that pass a given point in one second. The frequency of a vibration is expressed using a unit called hertz.  One hertz (Hz) is one vibration (one back and forth motion or one crest and trough combination) per second.  For example:  when a tuning fork with a frequency of 256 Hz is struck, it will vibrate 256 times in one second.
 

The period is the time it takes fro one complete vibration.  The period is inversely related to the frequency.  As the period increases, the frequency decreases.  As the period decreases, the frequency increases.
 

The velocity (related to speed) of a wave depends on the wavelength and the frequency of a wave.  The velocity of a wave is the wavelength times the frequency of the wave.
 

In transverse waves, such as light and water waves, matter moves up and down at right angles to the direction in which the wave moves (direction of propagation).
 

In compression waves, such as sound waves, matter vibrates in the same direction as the wave moves.  Compression waves travel through solids, liquids, or gases.  Instead of troughs and crest, compression waves have areas of compression and rarefaction.  Areas of compression are places where molecules are crowded together and areas of rarefaction are areas where molecules are spread out.  The wavelength of a compression wave is the distance from one compression to another or from from one rarefaction to another.
 

When a person speaks, vibrations of the vocal cords produce sound waves.  Sound waves usually travel faster through solids than through liquids or gases.  Since they require a medium to travel through, sound waves will not travel through a vacuum.
 

The loudness of a sound, often referred to as the intensity, is dependent upon the amplitude of the wave.  As amplitude increases, loudness increases.  The intensity of a sound is expressed in units called decibels.  The intensity of a sound is related to the pressure on the eardrum.  A sound of 120 decibels is intense enough to cause pain in the ear.  The softest sound that can be heard is 0 decibels, while normal talking is about 65 decibels.
 

The pitch of a sound refers to its highness or lowness.  The pitch of a sound depends on frequency.  The higher the frequency, the higher the pitch.  The pitch of a sound changes when the sound or the listener moves.  When you listen to a siren on an approaching vehicle, the pitch of the sound appears to increase as the vehicle approaches (pitch decreases for vehicle going away).  However, the pitch of the sound does not change.  Instead, the number of vibrations that reach your ear is changed when the source of the sound moves.  Therefore, the pitch appears to be higher or lower depending on whether the sound is moving toward or away from you.  This rise and fall of pitch due to relative motion between the observer and the source of the sound is called the doppler effect.