Post on 10-Mar-2018
Intro
Write the following questions on a blank piece of paper (don’t answer yet)
1. What is the difference between a mechanical and
electromagnetic wave?
2. What is the difference between a transverse and
longitudinal wave?
3. What do all waves transfer?
4. What don’t waves transfer?
• 23) analyze the properties of waves (GPS, HSGT)
• 23a) describe waves as a means of transporting energy (GPS)
• 23b) explain the production and propagation of waves created by simple harmonic motion (i.e., pendulum/spring motion) (GPS)
• 23c) compare and contrast mechanical and electromagnetic waves (GPS)
• 23d) compare and contrast longitudinal and transverse waves (GPS)
• 23e) explain the relationship between wavelength, frequency and wave speed (GPS)
• 23f) demonstrate and explain the general wave properties of reflection, refraction, interference and diffraction (GPS)
• 23g) explain the relationship between the phenomena of interference and the principle of superposition (GPS)
• 23h) demonstrate and explain wave phenomena using various types of equipment (i.e., ripple tank, slinky, soft rope, signal generator and oscilloscope) (GPS)
• 24) analyze the properties of sound (GPS, HSGT)
• 24a) explain the relationship between wavelength, frequency, period and wave speed as applied to sound waves (GPS)
• 24b) demonstrate apparent frequency changes due to Doppler Effect (GPS)
• 24b1) solve problems of apparent frequency changes due to Doppler Effect (GPS)
• 24c) use the law of reflection as it applies to echoes (GPS)
• 24d) explain the relationship of the speed of sound to temperature and elasticity of a medium (GPS)
• 24e) illustrate interference of sound waves to produce harmonics and resonance in various types of musical instruments, sound recordings, stringed instruments, open and closed pipes, and percussion (GPS)
• 24f) identify ranges for infrasonic, ultrasonic, and audible sounds
• 24g) describe applications of sound to sonar, ultrasound, and bats (GPS)
• Waves
– Are disturbances that move through an empty space
or through medium (material)
– Waves transfer energy without transferring matter.
– Particles of medium move in simple harmonic motion
Mechanical: Through a medium Electromagnetic:
Through empty space
• Mechanical wave:
– Caused by a disturbed medium and move by action
reaction of particles
– ex: water wave, sound
• A medium is matter particles like gas (ex. air),
liquid (ex. Water), and solid (ex. earth)
Two types of mechanical waves that require a medium
Transverse
Wave
Longitudinal
Wave
Electromagnetic wave:
• Move through empty space (no medium)
• Created by moving electrons
• Ex. radio waves, microwaves, light
Through empty space
Types Electromagnetic Waves
• In order to start and transmit a wave, a
source of disturbance (vibration) and a
disturbed medium are required.
• Mechanical caused by vibrating particles
– Like seen here
• Electromagnetic by vibrating electrons
Damping:
• A decrease in the amplitude of a wave
• Caused by energy loss or the spreading
out of the wave over a larger area.
• Wave pulse is a single wave disturbance
• Wave train (continuous wave) - is a
series of pulses at intervals
Transverse Wave:
• Wave particles move perpendicular to the direction the wave travels
• Ex. vibrating string of a musical instrument
Pe
rpe
nd
icu
lar
to t
he
dir
ec
tio
n o
f tr
ave
l
Direction of
travel
Parts of a transverse wave
Crest
Trough
Equilibrium
Position
Wavelength (ג)
Wavelength (ג)
Wavelength (ג)
amplitude
amplitude
• Crest- highest point on a transverse wave
• Trough- lowest point on a transverse wave
• Equilibrium position- center around which simple harmonic motion occurs
• Amplitude- from the equilibrium position to the crest or trough
Longitudinal Wave:
• Particles vibrate parallel to the direction
the wave travels
• ex. sound wave
Direction of travel
Particles vibrate parallel to the direction of travel
Parts of a Longitudinal Wave:
• Compression- point where the particles
are closest together
• Rarefaction- point where the particles are
furthest apart
Compression
Rarefaction
So, a couple of questions…
1. What starts a wave?
2. Sound is a (mechanical or electromagnetic) (transverse or longitudinal) wave.
More Questions
1. What do all waves transfer?
2. What don’t waves transfer?
3. What starts a wave?
4. Sound is a (mechanical or electromagnetic) (transverse or longitudinal) wave.
More Questions
1. What do all waves transfer? Energy
2. What don’t waves transfer?
3. What starts a wave?
4. Sound is a (mechanical or electromagnetic) (transverse or longitudinal) wave.
More Questions
1. What do all waves transfer? Energy
2. What don’t waves transfer? Matter
3. What starts a wave?
4. Sound is a (mechanical or electromagnetic) (transverse or longitudinal) wave.
More Questions
1. What do all waves transfer? Energy
2. What don’t waves transfer? Matter
3. What starts a wave? Disturbance in a medium
4. Sound is a (mechanical or electromagnetic) (transverse or longitudinal) wave.
More Questions
1. What do all waves transfer? Energy
2. What don’t waves transfer? Matter
3. What starts a wave? Disturbance in a medium
4. Sound is a (mechanical or electromagnetic) (transverse or longitudinal) wave.
• velocity ( v ): speed of the wave.
– unit: m/s (meter/second)
• frequency ( f ): vibrations per second of
the wave
– unit: Hz (hertz)
• wavelength ( ג ): length of one wave pulse
– unit: m (meter)
Lets revisit our old equation
What is the velocity of an object that moves
25 meters in 3 seconds?
V= ___ d
t
Lets revisit our old equation
What is the velocity of an object that moves
25 meters in 3 seconds?
V= ___ d
t
Now lets look at the new equation you can
use as well.
V= ___ d
t
old new
Example what is the velocity of a wave that has a
frequency of 3Hz and a wavelength of 5m?
Relationship between frequency and
wavelength.
• Wavelength and frequency are inversely
related
• As frequency goes up the wavelength gets
shorter (assuming no change in velocity)
Click for animation
Period (T) vs. Frequency (f)
• Period (T) – seconds for one cycle
– (unit s)
• Frequency (f) – cycles for one second
– (unit Hz)
• If you know one you can solve for the other
Example 2 Wave Math
A girl floats in the ocean and watches 12
wave crests pass her in 46 s. Calculate the
wave: a) frequency b) period
A girl floats in the ocean and watches 12
wave crests pass her in 46 s. Calculate the
wave: a) frequency b) period
Example 3 Wave Math
The period of a wave is 0.044s. How many
cycles will the energy source make in 22s?
cycles
second
Example 4 Wave Math
A distance of 0.33 m separates a wave crest from the adjacent trough, and the vertical distance from the top of a crest to the bottom of a trough is 0.24m.
A. What is the wavelength?
B. What is the amplitude?
0.33m
0.24m
Example 4 Wave Math
A distance of 0.33 m separates a wave crest from the adjacent trough, and the vertical distance from the top of a crest to the bottom of a trough is 0.24m.
A. What is the wavelength?
B. What is the amplitude?
0.33m
0.66m
Example 4 Wave Math
A distance of 0.33 m separates a wave crest from the adjacent trough, and the vertical distance from the top of a crest to the bottom of a trough is 0.24m.
A. What is the wavelength?
B. What is the amplitude?
0.24m 0.12m
Example 6 Wave Math
You dip your finger into a pan of water 14 times in 11s, producing wave crests separated by 0.16 m.
A. What is the frequency?
B. What is the period?
C. What is the velocity?
Example 6 Wave Math
You dip your finger into a pan of water 14 times in 11s, producing wave crests separated by 0.16 m.
A. what is the frequency
B. What is the period
C. Velocity