Crave the Wave

In Crave The Wave, participants will demonstrate knowledge and process skills needed to solve problems and answer questions regarding all types and areas of waves and wave motion. A calculator is required for this event.

Regionals Topics

 * General Wave characteristics- Wavelength, amplitude, frequency, period.
 * Wave Types- Transverse, longitudinal, surface, torsional waves.
 * Wave Phenomenon- Sound, light, reflection, standing waves, constructive and destructive interference, refraction, effect of media diffraction, Doppler effect.
 * Electromagnetic Waves- Electromagnetic spectrum, relationship between frequency and wavelength, energy carried (AM/FM only), standard wavelength bands, their uses and dangers. Others are about how the electromagnetic spectrum relates to everyday life and the knowledge of mechanical and electromagnetic waves.
 * Spectroscopy- Primary colors of light, use of filters, primary colors of pigments, absorption and emission spectra and their purpose in astronomy

Some calculations are required, such as calculation of frequency, period, wavelength, and speed.

Wave Characteristics
The main parts of a transverse wave are the crest, trough, wavelength, and amplitude. Also, there are additional characteristics of waves, such as frequency and period.


 * Crest- the highest point of a wave. Also called peak.
 * Trough- the lowest point of a wave.
 * Rest position- the position the wave would be in if there are no disturbances along it
 * Wavelength- the distance between two crests or troughs. Measured by distance units of the metric system.
 * Amplitude- the distance between a crest or trough and the rest position. Measured by distance units of the metric system.
 * Frequency- the number of times a wavelength passes a point in one second. Measured in Hz.
 * Period- the time a wave takes to complete a wavelength. Measured in seconds.

Some of these parts are shown in the picture below:



Types of Waves
The two main types of waves are longitudinal (Also called a P-wave) and transverse (Also called a S-wave). Transverse waves propagate perpendicular to the direction of the wave. Longitudinal waves move parallel to the direction of the wave. These two wave types can be modeled with a Slinky. Start by having two people stretch a Slinky. To model a transverse wave, have one person shake their end of the Slinky with an up-and-down or a right-to-left motion. To model a longitudinal wave, keep the Slinky completely straight and have one person quickly push their end of the Slinky to the other person.

Other types of waves include surface waves and torsional waves Surface waves are waves that travel along the boundary of two media. The particles in a surface wave move in a circular motion. Torsional waves twist and spin. It is like a screw being drilled, or moving your arms back and forth while keeping them flat.

Doppler Effect
The Doppler Effect is a difference in the frequency of a wave caused by a source moving relative to the observer. The Doppler Effect occurs because when an object emitting a wave is moving, the crests of the wave will bunch up in front of the object and the crests of the wave will be more spread out behind it. This causes a higher frequency of a wave when its source moves towards the observer and a lower frequency of a wave when its source moves away from the observer. An example of this is a siren passing by. It will sound higher pitched as it approaches, but then sound lower after it passes. The following equation is used to calculate the frequency of a wave using the Doppler effect: $$f=\left (\frac{c+v_r}{c+v_s} \right )f_0$$. $$f$$ is the observed frequency, $$f_0$$ is the emitted frequency, $$c$$ is the wave's velocity in the medium, $$v_r$$ is the velocity of the observer relative to the medium, it is positive when the observer moves towards the source and vice versa, $$v_s$$ is the velocity of the source relative to the medium, it is positive when the source moves away from the observer and vice versa.



Refraction
Refraction is the change in direction of a wave caused by a change in its medium. The index of refraction, also called refractive index, is a measure of how light refracts in a medium. Its formula is $$n=\frac{c}{v}$$. n is the refractive index, c is the speed of light in a vacuum, and v is the speed of light in that medium. Snell's Law states that the ratio of the velocities of a wave in two media is equal to the ration of the sine of the angles of incidence, which is also equal to the reciprocal of the ration of the refractive indices. The formula is $$\frac{\sin \theta_1}{\sin \theta_2}=\frac{v_1}{v_2}=\frac{n_2}{n_1}$$. $$\theta$$ is the angle of incidence, which is measured from the normal, v is the velocity in the medium, and n is the refractive index.

State Topics
At States you will also need to demonstrate your knowledge about seismic waves.

Seismic Waves
There are 5 major earthquake waves:


 * 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 cannot 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.

National Topics
In addition to the Regional and State topics, Nationals will introduce Breaking ocean waves and Tsunamis.

Equations to Know
There are several helpful formulas and equations to know.
 * Frequency
 * Frequency=1/Period
 * Period
 * Period=1/Frequency
 * Speed
 * Speed=Distance/time
 * Snell's Law
 * $$\sin <I \cdot n_1=\sin <R\cdot n_2$$
 * Rayleigh criterion
 * Young's Equation
 * Gratings
 * Harmonics and Resonant Frequency
 * Polarization
 * Brewster's Angle
 * Energy of a Photon
 * Dimensional Analysis
 * Wavelength of Colors

Sample Questions
If the frequency is 2 Hz (2 cycles per second), what is the wavelength?

If the wavelength is 2 cm, what is the frequency in Hz (cycles per second)?

If the period is 2 seconds, what is the Frequency?

What is Destructive Interference?

Which seismic wave is faster? Primary waves or Secondary waves?

Given an image of a wave, identify the wavelength.

Sample Exercises
[[Media: 2008 Crave the Wave State Test.pdf|Crave the Wave State Test (2008)]]

[[Media: 2009 Crave the Wave Practice Test.pdf|Crave the Wave Test (2009)]]

Websites and Resources
[[Media:Crave the Wave Resource Binder.pdf|A Crave the Wave Resource Binder (2007-2008)]]

Introduction to Waves

Sound Waves

Light and Color

Reflection and the Ray Model of Light

Refraction and the Ray Model of Light