View
3
Download
0
Category
Preview:
Citation preview
Chapter 14: Waves
What’s disturbing you?
Wave Properties
Waves carry energy through matter.
The matter can move with the wave, or at
right angles to it.
Newton’s laws and conservation laws
govern the behavior of waves as well as
particles.
All waves transmit energy. Some we see
and some we cannot, like sound and light.
What are Waves?Rhythmic disturbances that carry energy
through matter or space are called waves.
Some waves require a medium to travel
through. These are called Mechanical waves.
Water, air, ropes, and springs can “carry”
energy through them.
Media can be solids, liquids, or gases. Some
are good carriers and some not so good…
Two types of waves
There are two different fundamental types of
waves:
Transverse Waves- the energy moves at
right angles to the direction of the medium. Water, light, waves on a rope, electromagnetic
waves, most waves move this way
Longitudinal Waves- the energy moves
parallel with the direction of the medium. Sound & slinky compressions are the only examples
of a longitudinal or compression wave. Most liquids &
gases transmit energy this way.
Identifying Waves
Measuring Waves
We can describe waves in several aspects:
Speed- Δd/Δt, speed depends on medium
Amplitude- maximum displacement from
rest or equilibrium. Greater amplitude is
caused by more work, thus more energy
(not more speed)
For waves of the same speed, the rate at
which energy is transferred is proportional
to the square of the amplitude. Double
amplitude transfers 4x as much
energy/sec.
Measuring waves cont’d
Wavelength (λ)- low points are troughs, high
points are crests, shortest distance b/t 2 identical
points on a wave is one wavelength (m).
Period (T)- the time it takes for a wave to make
one complete cycle (oscillation). (s)
Frequency (f)- the number of cycles per second
(Hz).
fT
1
Tf
1
Wave Speed
Both period and frequency of a wave
depend only on the wave source; not speed
or medium.
Wavelength depends on both frequency
and wave speed. Speed of a wave is
wavelength divided by period, so
Wave speed is frequency times
wavelength.
fvT
v
Example Problem
A sound wave produced by a clock chime is
heard 515 m away, 1.5 s later.
a. What is the speed of sound of the
clock’s chime in air?
b. The sound wave has a frequency of
436 Hz. What is its period?
c. What is its wavelength?
Problem Solved
Given: d = 515m, t=1.5s, f=436 Hz
v = d / t, T = 1/f
a. v = 515m / 1.5s = 343m/s
b. T= 1/f = 1/436Hz, T=2.29x10-3s
c. λ = v / f = (343m/s) / (436Hz) = 0.787m
Your turn to Practice 14.1
Do Practice Problems # 2-7 pg 335
Do Ch 14 Review pg 344 #s 3 & 4
Do Ch 14 Review pg 345 #s 6, 7, 11, 24,
25, 26, 28, 30
Do Ch 14 Review pg 346 #s 33 & 36
Wave Behavior When a wave reaches a boundary, some of the
wave reflects back into the original medium, and some of the wave is transmitted into a new medium.
The amount of reflection or refraction depends on rigidity of the medium.
Waves at Boundaries
Remember the speed of a wave through a
medium depends on the properties of the
medium, not wave amplitude or frequency.
In air, temperature affects speed.
In water, depth affects speed.
In solids, rigidity affects speed.
Waves striking boundaries may be
returned to their medium (reflected), or
passed through to the next (transmitted).
Boundaries cont’d
An incoming wave is called an INCIDENT
WAVE.
If an incident wave strikes a barrier and is
transmitted, the pulse remains upward.
If an incident wave strikes a barrier and is
reflected, the pulse returns to the original
medium and can be inverted.
Reflected waves can lose amplitude and
transfer energy to the barrier. The wave’s
speed does not really decrease.
Superposition
Unlike particles of matter, 2 or more waves
can exist in the same space at the same
time.
The medium will be displaced an algebraic
equivalent to the sum of the individual
displacements.
This is called interference and can
increase (Constructive) or decrease
(Destructive) the amplitude of the new
wave.
Wave Interference Interference can produce
points of zero displacement
called nodes.
Points of maximum
displacement are called
antinodes.
Standing waves appear to
stand still due to
interference at just the right
frequency.
Waves in two-dimensions
Ray diagrams help model the movement
of waves in 2 dimensions.
A line perpendicular to the barrier is the
“normal”
The angle an incident ray makes with the
normal will be equal to the angle a
reflected ray makes with the normal
This is the law of reflection and holds true
for all types of waves.
Reflection and Refraction
Waves that return to their medium reflect from a surface following the law of reflection.
Waves that pass through to another medium refract or bend due to a change in speed in the new medium.
Diffraction
Waves may bend AROUND a
barrier they encounter.
Bending around the edges
without changing media is
called diffraction.
Diffraction also occurs when
waves meet a small obstacle.
They can bend around it and
fill in behind it.
Diffraction and Interference
For multiple openings,
waves bend and
interfere with each
other creating
constructive (large
waves or bright
areas) and
destructive (reduces
waves or dark areas)
interference patterns.
Your turn to Practice
Please do Ch 14 Review p 345 #s 20, 22,
23, 45, & 47
Recommended