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Waves
Learning Objectives• TLW know the characteristics and behaviors of
waves (TEKS 7)• TLW conduct lab investigations in a safe manner
(TEKS 1)• TLW use scientific methods during lab (TEKS 2)• TLW uses critical thinking and problem solving
techniques to make informed decisions (TEKS 3)
I. What is a Wave?A. Wave – a disturbance that carries
energy through matter
1. The matter through which a wave travels is called a mediumEx. A rock thrown in water = water is the medium
Ex. A stereo playing music = air is the medium
Ex. Earthquake travels through earth = ground is the medium (these are called seismic waves)
2. The density of the medium is called
elasticity
3. It is the energy that moves not the matter (or water)
4. A wave can occur in water, air, or space * = anywhere (* except sound doesn’t travel in the vacuum of
space)
5. Sound and light travel as a
wave
Characteristics of Waves
• Wavelength – distance between 2 crests or 2 troughs or any other identical points
• Wave height – distance between a crest and a trough
• Amplitude – ½ the distance between a crest or a trough
Parts of a Wave
Amplitude
Wave height
amplitudewave height
• Frequency – number of wavelengths that pass a point in a certain time
–Also measures how rapidly vibrations occur in the medium
• Wave period – the time required for 1 wavelength to pass a certain point
CalculationsA mathematical relationship exists between wave speed
(velocity), wave length, and frequency
Wave speed = wavelength x frequency
It can be described by the formula:
v = λ f
Where
v = wave speed in m/s (velocity = distance/time)
λ = wavelength in m
f = frequency in Hz (which is the same as 1/sec)
or f = 1/T where T is time in seconds
Practice Calculation
If a wave has a wavelength of 10 m and a frequency of 2 Hz, what is the wave speed?
Given: v = λ f
λ = 10 m (10 m)(2 Hz)
f = 2 Hz 20 m/s
B. Types of Waves
1. Mechanical Waves
a. Any wave that travels through a medium is a mechanical wave
b. Ex. Sound waves, water waves, seismic waves
c. Almost ALL waves are mechanical waves
2. Electromagnetic Wavesa. A wave that does NOT require a
medium
b. Occurs when energy “travels”
through electric and magnetic
fields by being propagated
by sub-atomic particles called
photons
c. Ex. Visible light, radio waves, x-rays
Wave-Particle Duality
• The theory that electromagnetism is made up of both energy and particles of matter (photons)
3. Movement of particles in mediuma. when a wave occurs particles
in the medium will moveb. particles will either move up
and down or back and forth
c. Waves are classified by thedirection the particles
move in a medium as a wave passes
d. Types of waves based on particle movement
1. Transverse waves
a. travels through solids, liquids &
gases
b. particles move perpendicular
or up and down
c. Bunched up part is called
compression
Transverse wave
2. Longitudinal waves
a. travels through solids,liquids & gases
b. a parallel motion or back & forth
Longitudinal wave
Types of Waves
Common Stuff
• Threshold of human hearing is 1,000 Hz (0 decibels – dB)
• Threshold of pain in human hearing is 4,000 Hz (120 dB)– Rock concert (100 – 150 dB)
• Any sound above 20,000 Hz is called ultrasound – like the safer way to observe an unborn child or lump
• The frequency of a sound wave is called pitch as a sensation (high frequency, high pitch)
More Common Stuff
• Range where humans can detect light is 400 nm – 700 nm (ROYGBIV)
C. Surface Waves1. If a wave has both transverse
and longitudinal waves it is called a surface wave
2. Ex. Ocean waves are examplesof surface waves
II. How a Wave WorksA. Energy must be transferred
1. Waves carry energy
2. the bigger the initial wave the more energy it has
B. The energy spreads out
1. waves spread out in spheres called wave fronts
2. as waves move away from the “center” the spheres or circles get larger
3. the entire wave has the same amount of total energy
4. but as the wave gets larger, that energy is more spread out
5. Eventually, the waves become so large that the energy is not “noticeable”
6. Ex. throwing a rock in a pond – the waves become larger and weaker the further
from the center it travels
Sound – the further from source the harder it is to hear
• TRUE or FALSE: In order for John to hear Jill, air molecules must move from the lips of Jill to the ears of John.
• Curly and Moe are conducting a wave
experiment using a Slinky. Curly introduces a disturbance into the Slinky by giving it a quick back and forth jerk. Moe places his cheek (facial) at the opposite end of the slinky. Using the terminology of this unit, describe what Moe experiences as the pulse reaches the other end of the slinky.
• Rhonda sends a pulse along a rope. How does the position of a point on the rope, before the pulse comes, compare to the position after the pulse has passed?
• Why don't incoming ocean waves bring more water onto
the shore until the beach is completely submerged? In order for a medium to be able to support a wave, the
particles in the medium must be – frictionless. – isolated from one another. – able to interact. – very light.
Reflection
http://www.slideshare.net/amandayoung313/how-do-waves-behave
Refraction
http://www.slideshare.net/amandayoung313/how-do-waves-behave
Diffraction
http://www.slideshare.net/amandayoung313/how-do-waves-behave
Interference
http://www.slideshare.net/amandayoung313/how-do-waves-behave
Destructive Interference
When wave interference is in the opposite direction.
This action tends to reduce amplitude of disturbance.
Constructive Interference
When wave interference is in the same direction.
This action tends to increase amplitude of disturbance.
Standing Waves
• Successive waves that interfere with each other in a way that causes them to stand still
Resonance•Resonance means to resound or sound again•When the frequency of a force vibration on an object matches the object’s natural frequency, a dramatic increase in amplitude occurs – this phenomenon is called resonance
•This is how tuning forks work
•Not only sound, but vibration in generalResonance from a mild gale force wind of 40 mph with the natural frequency of the Tacoma Narrows Bridge (in Washington state) in 1940 caused collapse in just one hour… only 4 months after bridge was completed
http://www.youtube.com/watch?v=3mclp9QmCGshttp://www.youtube.com/watch?v=j-zczJXSxnw
RarefractionDecrease in density and pressure in a medium, such as air, caused by the passage of a sound wave.
Rarefaction can be easily observed by compressing a spring and releasing it. Instead of seeing compressed loops seeming to move through the spring, spaced-out loops move through it: rarefaction waves.
The Doppler EffectThe apparent frequency of a sound changes due to the relative movement of the source and/or observer
YouTube - Fire Engine siren demonstrates the Doppler Effect
Uses of the Doppler Effect
• Measuring the speed of moving objects (like cars or baseballs)
• Measuring the speed of flow of blood cells in an artery
• Meteorologists use the Doppler Effect to track storm systems
• The same effect occurs with light waves. This is how scientists have proven the universe is expanding (called the Red Shift)
• Doppler Slides from Google link
Lens• Lens are optical devices that transmit and
refract light
eye glasses, microscopes
• Converging lenses focus
light to a single point
• Diverging lenses
spread the light outward
Web Waves
Discovery Education web video
Elements of Physics: Waves: Sound and Electromagnetism
link
Labs
• In Periodic Groups review entire procedure
• Determine any potential hazards, precautions to take, and PPE needed (if any)
• Complete any pre-work associated with lab
• Set up experiment and report using scientifc method
Lab
• Various options
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