Physics

Vandebilt Catholic High School

W. Dupre

Waves

Wave

- traveling disturbance that transmits energy without transferring matter

Types of waves:

1. Electromagnetic
• Examples -- light waves, radio waves, microwaves, X-rays, etc.
• Do not require a medium for transfer; can be transferred through a vacuum
2. Mechanical
• Examples -- sound waves, water waves, etc.
• Require medium for transfer; cannot be transferred through a vacuum
• The speed of the wave depends upon the mechanical properties of the medium.
• Some waves are periodic (particles undergo back and forth displacement as in a sound wave.)
• Some waves are sinusoidal (paricles undergo up and down displacement as in a wave on a string.)

Types of mechanical waves:

1. Transverse

As a wave passes through a point, the particles vibrate at right angles to the direction in which the wave is moving

Notice -- as the wave moves through point A, the particle does not return to its original position until point E

Crest

upward displacement of transverse wave

Trough

downward displacement of transverse wave

2. Longitudinal

As wave passes through a point, the particles vibrate parallel to the direction in which the wave is moving

Wave terms:

1. Wavelength

the distance between two successive in-phase points; symbol is l and SI unit is meters

2. In Phase

Points on a wave that are in the same orientation. In the wave below points “A” & “F” or in phase. So are points “C” and “H”

3. Out of Phase

Points in a wave that are not in the same orientation. In the wave above points “A”, “B”, “C”, “D”, & “E” are out of phase with points “A” & “D” are 180^O Out of phase.

4. Amplitude

maximum displacement of wave; measure of wave's energy

5. Pulse

single disturbance of a medium

6. Frequency

the number of waves passing a point per second; symbol is f and SI unit is Hertz (Hz)

7. Period

time for one wave; symbol is T and SI unit is second

T = 1/f

f = 1/T

8. Speed

the speed with which the wave moves through the medium is dependent upon the properties of the medium only. It is determined by the ratio of the elastic properties of the medium to the inertial properties of the medium. The speed can be calculated by finding the product of the wavelength and the frequency; SI unit is m/s

v = l n or v = l f

Wave Behaviors

1. When a wave approaches a boundary between two different media three things may happen.

a. The wave can completely transmit into the new medium. This will only occur if the two media’s properties are exactly alike.

b. The wave can completely reflect back into the old medium. This will happen if the two media’s properties are exactly opposite of each other.

c. The wave will partially transmit into the new medium and partially reflect back into the old medium. The amount of transmission and reflection will be determined by the degree of difference between the two media.

1) The more alike the two media the more the wave will transmit.

2) The greater the difference the greater the reflection.

2. The transmitted wave will always remain upright (in its same orientation)

3. The reflected will:

a. remain upright (in the same orientation) if the wave is traveling from a more dense medium to a less dense medium.

b.

Invert (flip orientations) if the wave is traveling from a less dense to a more dense medium.

1. Interference - result of the superposition of two or more waves
• Superposition Principle - when two waves are in the same place at the same time, (only waves exhibit this behavior, particles cannot do this)the displacement caused by the waves is the algebraic sum of the two waves

• Constructive interference

waves interfere, "adding" to produce a larger wave

• Destructive interference

waves interfere, "adding" to produce a smaller wave

• Standing Waves

two waves with the same wavelength, the same frequency, and the same amplitude that are traveling through a medium in opposite directions interfere producing a standing wave

Node

point of zero displacement on a standing wave (destructive interference)

Antinode

point of maximum displacement on a standing wave (constructive interference)