Crave The Wave
Division B 2016
By: Beth Lewis
10/9/2015
Contact: beth_lewisfamily@yahoo.com
The Exam Nuts and Bolts
• Lab Practical
• 25 minutes in length
• 4 stations – 5 min each
• Theoretical questions
• 25 minutes in length
• 12 stations – 2 min each
A team may consist of up to 2 students.
Competitors may bring reference materials, writing utensils, protractors, rulers and any type of calculators.
All reference materials must be secured in a 3-ring binder, so that regardless of orientation nothing can fall out.
Exam scoring: Points must be awarded for the accuracy and quality of the responses. High score wins.
Theoretical Questions
• How to identify the following for a
given wave:
•
Peak/Crest
•
Trough
•
Wavelength
•
Amplitude
•
Period/Frequency
•
Speed
•
Energy
Excellent References:
Diagram taken from : www.physicsclassroom.com
Peak/Crest: Points A, E H
Trough: Points C, J
Wavelength: horizontal distance between adjacent peaks or troughs that measures
one wave cycle. Distance between points A and E or E and H or D and G
http://www.physicsclassroom.com/Class/waves/u10l2a.cfm
Amplitude: ½ the vertical height between a peak and trough. ½ the height between
points C and E or C and A or the height between points D and E or G and H.
http://www.physicsclassroom.com/class/waves/Lesson-2/Frequency-and-Period-of-a-Wave
Interactive learning for your students:
Period: the time it takes for one wavelength to repeat. Time between points A and E
or E and H or D and G (measured in sec)
The Slinky Lab: http://physics.appstate.edu/laboratory/quick-guides/waves-slinky
http://www.whrhs.org/cms/lib07/NJ01001319/Centricity/Domain/94/Slinky%20lab.pdf
Online interactive learning:
http://www.physicsclassroom.com/Physics-Interactives/Waves-and-Sound/Slinky-Lab/SlinkyLab-Interactive
Frequency: 1/Period (measured in Hz = 1/(sec))
Speed: speed = wavelength x frequency : wave speed is dependent on medium
properties. For a given material, the wave speed is constant.
Energy: wave energy is proportional to (Amplitude)^2
Different Types of Waves
• Transverse Waves : a wave in which
the particles of the medium are displaced in a
direction perpendicular to the direction of
energy transport/wave propagation.
• Longitudinal Waves: a wave in which
the particles of the medium are displaced in a
direction parallel to the direction of energy
transport/wave propagation
Compression
Rarefaction
Sound Waves
Electromagnetic Waves
Illustrations taken from: http://hyperphysics.phy-astr.gsu.edu/hbase/sound/tralon.html
Excellent online video to illustrate the difference between Transverse and Longitudinal Waves:
Transverse and Longitudinal Waves in Physics: https://www.youtube.com/watch?v=jAXx0018QCc
Different Types of Waves
• Surface Waves: A surface wave is a wave in
which particles of the medium undergo a circular motion.
Surface waves are neither longitudinal nor transverse. In
longitudinal and transverse waves, all the particles in the
entire bulk of the medium move in a parallel and a
perpendicular direction (respectively) relative to the
direction of energy transport. In a surface wave, it is only
the particles at the surface of the medium that undergo
the circular motion. The motion of particles tends to
decrease as one proceeds further from the surface.
• Torsional Waves : a torsional wave causes
the material to twist about a central axis.
Illustration take from
www.ck12.org
Illustration taken from : moodle.davidson.edu
Ocean or Earthquake Waves
Excellent online video to illustrate Surface Waves:
Waves on the Surface of Water HD : https://www.youtube.com/watch?v=7yPTa8qi5X8
http://dev.physicslab.org/document.aspx?doctype=3&filename=wavessound_introductionwaves.xml
http://physics.info/waves/
Found in structures such as buildings and bridges
Excellent online video to illustrate Torsional Wave:
Wave Machine Demonstration : https://www.youtube.com/watch?v=VE520z_ugcU
Wave Phenomena: Reflection
• Reflection refers to the change in direction as a wave bounces off of a
barrier or surface. The angle of incidence, ϴI, equals the angle of
reflection, ϴr. ϴI = ϴr
I = the incident wave
R = the reflected wave
Image taken from:
http://www.physicsclassroom.com/Class/refln/u13l1c.cfm
N = the normal line – a line perpendicular to the surface.
Wave Phenomena: Refraction
• Refraction describes a change in direction when waves travel from one material to
another. As well as a change in direction, the wave speed and wavelength change – the
wave frequency stays the same. Wave speed depends on the material’s density. The
higher the material’s density, the higher the wave speed in that material. The faster the
wave speed in the material, the stronger the bend in the direction of the normal.
Image taken from: http://www.physicsclassroom.com/class/refrn/Lesson-2/The-Angle-of-Refraction
Wave Phenomena: Diffraction
• Diffraction describes how waves change direction when they move through an opening or move
around a barrier. The amount of diffraction (sharpness of the bending of the wave) is large for
wavelengths longer than the barrier or opening. The amount of diffraction gets smaller as the
wavelength decreases and diffraction will not occur when the wavelength is smaller than the size
of the barrier or opening.
Images taken from: http://www.schoolphysics.co.uk/age14-16/Wave%20properties/text/Diffraction_/index.html
Wave Phenomena: Doppler Effect
• The Doppler Effect is observed whenever the source of the waves is moving with respect to an
observer. There is an apparent upward shift in frequency for observers towards whom the source
is approaching and an apparent downward shift in frequency for observers from whom the
source is receding. The actual frequency emitted by the source is not shifted.
Image taken from: http://www.physicsclassroom.com/class/waves/Lesson-3/The-Doppler-Effect
Wave Phenomena: Interference
Interference occurs when two waves meet while traveling along in a material.
• Constructive Interference occurs when two
waves have amplitudes in the same direction.
The Green line represents the wave that will be observed
as a result of the constructive interference. It is the sum
of the amplitudes of the red and blue waves.
Images taken from: http://www.physicsclassroom.com/class/waves/Lesson-3/Interference-of-Waves
• Destructive Interference occurs when two
waves have amplitudes in the opposite
direction.
The Green line represents the wave that will be observed
as a result of the destructive interference. It is the difference
of the amplitudes of the red and blue waves.
Wave Phenomena: Standing Waves
• A standing wave pattern can occur when a wave is not free to move throughout a material, but is
confined (or fixed) at a boundary. When the initial wave hits the boundary, its energy is reflected and
the reflected wave interferes with the initial wave to create a new wave pattern. A special pattern is
created when the frequency is just right so that there are specific points along the new wave pattern
that have zero amplitude and don’t appear to move in time – they appear to be “standing still”.
Nodes are where the standing wave has zero amplitude.
Antinodes are where the standing wave has maximum
Amplitude – both positive and negative.
Image taken from: http://www.physicsclassroom.com/class/waves/Lesson-4/Nodes-and-Anti-nodes
Wave Phenomena: Standing Wave Harmonics
A variety of different wave patterns can be created by varying the frequency of the initial wave when creating
standing waves. Remember only certain frequencies can create these standing wave patterns called Harmonics.
Harmonic
# of Nodes
# of Antinodes
1st
2
1
2nd
3
2
3rd
4
3
4th
5
4
5th
6
5
6th
7
6
Outstanding video demonstration here:
https://www.youtube.com/watch?v=-gr7KmTOrx0
Standing Waves Part I Demonstration
Pattern
Chart taken from:
http://www.physicsclassroom.com/class/waves/Lesson-4/Harmonics-and-Patterns
Electromagnetic Waves
Light exhibits several wave-like characteristics: reflection, refraction, diffraction, interference and the Doppler
Effect. Light travels via a transverse wave that has both an electric and magnetic part. It does not need a
medium to travel through – it can travel through a vacuum.
The range of frequencies for which electromagnetic waves exist is called the electromagnetic spectrum.
Fun Fact: Light used to
“see” an object must have a
Wavelength about the same size
Or smaller than the object. Can we
Use visible light to see molecules?
Image taken from Lawrence Berkley National Lab: http://www2.lbl.gov/MicroWorlds/ALSTool/EMSpec/EMSpec2.html
Excellent info at NASA: http://imagine.gsfc.nasa.gov/science/toolbox/emspectrum1.html
Spectroscopy: Primary Colors of Light
• White light is the presence of all the frequencies of visible light. When we speak of white light, we
are referring to ROYGBIV - the presence of the entire spectrum of visible light. But combining the
range of frequencies in the visible light spectrum is not the only means of producing white light.
White light can also be produced by combining only three distinct frequencies of light, provided
that they are widely separated on the visible light spectrum. Any three colors (or frequencies) of
light that produce white light when combined with the correct intensity are called primary colors
of light. There are a variety of sets of primary colors. The most common set of primary colors is
red (R), green (G) and blue (B). When red, green and blue light are mixed or added together with
the proper intensity, white (W) light is obtained. The color addition rules are illustrated below:
Images taken from: http://www.physicsclassroom.com/class/light/Lesson-2/Color-Addition
Spectroscopy: Color Subtraction
”Visible light of many frequencies or even all frequencies is incident towards the surface of objects. When this occurs, objects
have a tendency to selectively absorb, reflect or transmit light certain frequencies. That is, one object might reflect green
light while absorbing all other frequencies of visible light. Another object might selectively transmit blue light while absorbing
all other frequencies of visible light. The manner in which visible light interacts with an object is dependent upon the
frequency of the light and the nature of the atoms of the object. The color of an object is not actually within the object itself.
Rather, the color is in the light that shines upon it and is ultimately reflected or transmitted to our eyes.”
from: http://www.physicsclassroom.com/class/light/Lesson-2/Light-Absorption,-Reflection,-and-Transmission
Excellent discussion plus exercises for color subtraction, filters, pigments, etc
Here: http://www.physicsclassroom.com/class/light/Lesson-2/Color-Subtraction
Filters
Images taken from: http://www.physicsclassroom.com/class/light/Lesson-2/Color-Subtraction
Spectroscopy: Absorption and Emission Spectra
• Glowing hot gas will emit light only at specific wavelengths. This pattern is different for each
element and is called the emission spectrum for that element. The emission spectra can be used
to identify elements found in astronomical bodies such as the sun and other distant stars.
• Cool gases will absorb light at the same specific wavelengths as the emission spectrum for that
gas. This inverse pattern is called the absorption spectrum for that element. The absorption
spectra can be used to identify elements found in the atmospheres of planets and stars.
Great references at NASA: https://solarsystem.nasa.gov/deepimpact/science/spectroscopy.cfm
If you want to go nuts with this topic, check out this lab designed for 8th-10th graders by NASA:https://www.nasa.gov/pdf/479659main_LP8-AnalyzingSpectra_508.pdf
Seismic Waves: State level only
• P-waves - aka primary waves, are longitudinal waves. They are the first to arrive. They can travel through
liquids.
• S-waves - aka secondary or shear waves, are transverse waves. They are second to arrive. They can not
travel through liquids.
• Surface Waves - combinations of P and S waves and occur on the surface. They are the slowest waves.
• Rayleigh Waves - waves that roll in an ocean-like motion.
• Love Waves - waves that move in side to side, horizontally. Love waves cause the most damage
Be sure to work through this awesome
exercise to learn how to find the
earthquake epicenter:
https://www.youtube.com/watch?v=TBss68oBmmk
Fantastic resource here and image taken from:
http://mjksciteachingideas.com/quakes.html