WAVES

WAVESTraveling disturbance Transfer of energy

2) Mechanical Wave - need a medium1) Electromagnetic Wave

1) transverse2) longitudinal

pulse

Two Wave Categories:

Two Types of Mechanical Wave Motions:

WAVESPeriodic Waves

(repeats a pattern, or cycle)

wavelength periodfrequency

amplitude(Related to the energy content of a mechanical wave)

fv

A sound wave traveling through air has a frequency

of 425 Hz and a wavelength of 0.800 meter. What is

the speed of this sound wave?

WAVES

WAVE SPEED

depends on material properties of the medium

(constant in a given medium)

LmFv

In a rope (or similar material), the speed of a wave is determined by:

Tension in rope

Linear density of rope

mkg

A transverse periodic wave is created in a rope of mass 2.00 kg

and length of 6.00 meters. The rope is under a tension of 150

N. The speed of the wave in the rope would be…

The wave cycles created in the rope have a period of 0.10

second. The wavelength of the “rope” wave would be…

WAVE SPEED

Tfv

You are in your car sitting at a red light when you hear an ambulance siren. You

can not see the ambulance, yet you know it is approaching you.

How can you tell the ambulance is moving toward you?

API

The intensity DECREASES as the distance from the source increases.

AtE

The siren is producing sound energy at a

rate of 3.6 W, and you are 10.7 meters away

from the siren. What is the intensity of the

sound at your location?

If your eardrum has an area of 0.50 cm2, how

much energy passes through your eardrum

in a time of 5.0 seconds?

What would the intensity be at a distance of

1070 meters?

Wave Behaviors

Reflection

Changing direction upon meeting a barrier (wave energy remains in original medium)

The polarity (orientation) of the wave may also be affected:

If the barrier is very rigid compared to the original medium, the reflected wave will be inverted (have the

opposite polarity of incident wave).

If the barrier is very flexible compared to the original medium, the reflected wave will be upright (have the

same polarity as incident wave).

How much of the wave energy will reflect?

If barrier material is very different from original medium, most of the wave energy will reflect.

If barrier material is very similar to original medium, very little of the wave energy will reflect. (Most will transmit through to

the new medium.)

Reflection

Path of reflected wave is determined by the Law of Reflection.

Reflection

ri (measured relative to the normal line)

(transmitted portion not shown)

Refractionchanging direction when the wave enters

a new mediumIncident wave must make θ > 0˚ to normal line.

Which way will it bend?

Caused by the wave changing speed when it enters the new medium.

If wave slows down, it bends toward the normal.

If wave speeds up, it bends away from the normal.

(Wave frequency remains the same.)

http://www.acoustics.salford.ac.uk/schools/teacher/lesson3/flash/whiteboardcomplete.swf

I have a BB machine gun, which emits a continuous stream of metal BB’s. I point it at a metal plate that has two openings in it and shoot.

If the metal plate is placed a certain distance in front of a plaster wall, what will I see on the wall when I move the plate away?

What if it is a beam of light instead?

Diffractionbending around obstacles in its path,

changing direction as a result

Wave speed remains constant since medium doesn’t change.

Wave frequency also remains constant.

The extent of the diffraction depends upon the wavelength of the waves (λ) and the size of the

obstacle (d).

d amt. diff. Generally:

InterferenceThe effect on the medium when multiple waves meet at the

same location.

constructive interference

Principle of Linear Superposition – the resulting disturbance is the sum of the individual wave

disturbances

destructive interference

circular wave interference(2D)

WAVESUpon entering a new medium…

…what changes?

…what remains the same?

speed, wavelength, amplitude, possibly direction

FREQUENCY