Post on 06-Jan-2018
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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.)
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