Properties of Light

Waves: Standard Dimensions

• In physics, waves are described by a few standard dimensions.

• Frequency f = how often wave crest passes, longer wavelength means lower frequency

• v = f x 

• Wavelength  = length of one cycle

• Amplitude A= height of wave above “rest position”

• Velocity v= speed of wave

Frequency and Period

• Frequency: how often a vibration (cycle, repetition) occurs in some interval of time, # vibrations (or cycles) per unit time.

• units are Hertz (Hz)
• 1-Hz = 1 vibration/sec = 1 cycle/sec

• 103 Hz = kHz (AM radio frequencies)

• 106 Hz = MHz (FM radio frequencies)

• Period: the time to complete one vibration (or cycle),

• the inverse of the frequency

• period = 1 / frequency OR frequency = 1 / period

Wave Speed

• The speed of some waves depends on the medium through which the wave travels.
• Sound waves travel at speeds of 330 - 350 m/s in air, and about four times as fast in water.
• The speed of the wave is related to the frequency and wavelength of the wave.
• Wave speed = frequency x wavelength

Motion of Waves

• Is there a relationship between
• the motion of the wave through space
• and
• the motion of the medium that a wave moves in?

Wave Types

• Two types of waves
• transverse
• longitudinal

• Cheerleader demo

Types of waves

• Transverse waves: the motion of the medium is at right angles to the direction in which the wave travels.

• Longitudinal waves: the particles in the medium move along the direction of the wave; travel in solids, liquids, and gases.

• Examples: stretched strings of musical instruments, waves on the surfaces of liquids, some of the waves produced in earthquakes.
• Although they require no “medium” to travel, electromagnetic waves are also transverse waves.

• Examples: sound waves, some of the waves produced in earthquakes.