Characteristics of Waves:

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.

Two Major Types of Waves:

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 one rarefaction to another.

Wave Equation:

V = λ • f λ = V • T f = 1 / T

where V = velocity, λ = wavelength (lambda), f = frequency, T = period

Electromagnetic waves (visible light, UV, infrared, TV, radio, microwave, gamma, etc.) travel at the speed of light (c) which equals 3.0 E 8 m/s or 186 282 miles/second

Using V = λ • f (and assuming v = c which is a constant)
a) increasing the λ decreases the f
b) decreasing the λ increases the f

example: 6 = 3 f ( f would = 2) 6 = 6 f ( f would = 1)

Using f = 1 / T
a) as T increases, f decreases
b) as T decreases, f increases

Using V = λ • f
a) Given a speed of sound of 352 m/s and a note "A" = 440 Hz:

352 m/s = λ • 440 Hz
λ = 0.8 m

All electromagnetic waves have different frequencies and different wavelengths, but the same speed (c = 3 E 8 m/s)
short wavelength = must have large frequency
long wavelength = must have smaller frequency

Radiation:

· there is no transfer of mass

· requires no material medium to propagate

· the energy being transferred is an electromagnetic disturbance

see drawing of electromagnetic wave

The magnetic and electric fields are being represented by a series of vectors (not lines of force) that indicate magnitude and direction of the fields in the path of the wave. The fields are perpendicular to each other and to the direction of the wave and remain in step as they periodically reverse their direction.

A heated, glowing body emits all wavelengths (entire spectrum) from radio waves (miles in length) to gamma radiation (less than
1 E -10 cm in length)

Review Items:

Node: displacement from central line = 0 (no motion)
Crest/Trough = antinode (maximum amplitude/disturbance)
Wavelength: distance between any two equivalent points
Frequency: count equivalent points passing in time (vps = vibrations per second or cps = cycles per second
Hertz = 1 vbs = 1cps = 1 Hz
Period = amount of time for particular event to occur
Amplitude = energy in wave
Energy of wave is proportional to square of amplitude. To double amplitude, it would take 4 times as much energy - if you reduce the energy by 100 (1% as much energy) you reduce the amplitude by factor of 10 (10% of original value).

Page Last Updated: Friday March 02, 2007 Webmaster: Larry Jones Pickens County School District