Judges determine the overall winner based on each team's score in the five different events.
The full range of light stretches from the lowest energy, longest wavelength radio waves to the highest energy, shortest wavelength gamma rays. Human eyes are sensitive to a small portion of the electromagnetic spectrum - in the range of wavelengths from about 400 nm to 700 nm (1 nm = 1 billionth of a meter).
A spectroscope (or spectrometer) is an instrument that causes each energy/wavelength to be redirected at a slightly different angle. The resulting spectrum allow for analysis of the amount of light that an object gives off as a function of energy/wavelength. Each physically different source of light has a unique and identifiable spectrum.
Sources of light that appear mostly the same to the naked eye can have completely different physical processes responsible for their emitted illumination. A rainbow is an example of the spectrum of visible sunlight. Modern civilization still uses sunlight as a light source, but we have come to rely more and more on artificial sources of white light illumination such as incandescent bulbs, fluorescent tubes, compact fluorescent bulbs, and light emitting diode (LED) lamps. Spectrometric analysis allows us to determine which physical process is producing the white light emitted by a particular lamp. The spectrum of an incandescent light bulb is very similar to the spectrum of sunlight – indicating that both are created by the same physical process. However, the spectra of a white LED lamp and a fluorescent lamp are different from that of sunlight, as well as from each other. Likewise, any white light (versus a light appearing red or orange-red, yellow-orange, yellow, green, blue, or purple to the naked eye) has observable features in its visible spectrum which indicate how the physical process responsible for its light create a different overall emission that appears different to the naked eye.
A spectroscope can be used to determine if the yellow light in a particular traffic signal is due to yellow LED lamps or to the transmission through a filter placed in front of an incandescent bulb emitting white light. Forensic scientists are able to determine the elemental content of a gas by measuring the wavelengths for which a spectrum produces bright emission. Astrophysicists rely on spectroscopy for most of our understanding of the cosmos. Spectral analysis of the glowing gas in remote galaxies allow us to know the composition of the early universe. The spectrum of a distant star allows us to determine its temperature; with the hottest stars appearing bluish and the coolest stars appearing reddish. Within our solar system, analysis of how each wavelength of the incident sunlight is either reflected or absorbed from a planet or moon is used to understand the material of that world’s surface.
Each team that registers by the established deadline will receive a diffraction grating to be used for the dispersive element of its spectroscope. The team is free to use any materials and methods to use this diffraction grating to create a spectroscope. There is not limit to the number of redesigns and rebuilds of the team’s spectroscope; however, the final version must be used to make all submitted observations and this version must be submitted for judging on the day of the competition.
Up to 20 points will be awarded for the construction of a spectroscope using the provided diffraction grating. During Saturday morning’s registration period each team must submit the spectroscope used to acquire the submitted spectral observations. Event judges will verify the instrument’s ability to measure the features identified in those submissions.
Each submission received by the due date will be judged according to the following criteria.
Overall rankings for this event are determined by greatest total sum of points earned for each submission by that team. Ties will be broken by the points earned for the explanation of the physical processes responsible for each observation.
Your team will be asked to divide into two groups. Two of you will be given spectroscopes (you are also allowed to use the spectroscope your team constructed for the Spectral Scavenger Hunt event), a pencil, and some blank graph paper, with the task of sketching the key features of the spectrum from each of the samples provided by the judges. The other two members will be provided with basic information about the processes responsible for discrete emission spectra, and have the chance to explore the differences in the spectrum from various elements. They will be presented with the first pair’s set of sketches and must correctly identify each source solely from these sketched spectra.
Activity is the key word for this competition, with the goal being for each team to achieve the desired results as quickly as possible. Following the International Year of Light theme, this event will test each team’s ability to apply the laws of reflection and refraction in a chaotic, time sensitive situation. The competition is designed to reward teamwork and common sense thinking as well as knowledge of physics. Every team will come away with smiles and good memories regardless of how well they master the particular challenge.
Arrive at a reasonable approximation for the value of a complex situation with very little to no information available to directly compute the answer. In this quiz, the contestants will need to quickly make assumptions for values to use in simple calculations in order to arrive at the "correct" answer, stated as the power of ten of the number that fits the accepted value.
Teams will receive 9 questions to complete within 15 minutes. The teams can divide the work in any way they see fit, but only one answer per question per team will be accepted. Answers will be judged according to how many orders of magnitude the team's answer is from the judge's solution. The lowest score wins -- 0 points awarded for the answer accepted by the panel of judges, with 1 point scored per order of magnitude from the accepted value.
Examples of Order-of-Magnitude Quiz questions include:
The year’s Plan-Ahead competition requires teams to measure the polarization of light for a given situation and use it to correctly determine the rotation of polarization internal to a material.
What is a light beam? A physicist’s definition is that light consists of time dependent transverse electric and magnetic waves propagating past a point in space. The oscillations of the electric and magnetic field are always synchronized to be perpendicular to each other and both perpendicular to the direction of travel for the wave. The polarization of the light is defined by the direction of the electric field component of the wave.
Unpolarized light passing through a polarizing filter will have its intensity reduced by a factor of ½. This occurs because only half the originally unpolarized light gets transmitted by the polarizer -- the half with polarization in the same direction as the alignment of the polarizer. Place another polarizer in the light beam, this time with the alignment of its polarizing filter at 90o to the first polarizer -- no light is transmitted through two polarizing filters that are oriented orthogonally. Learn more about polarization at websites such as arborsci.com/cool/polarization or lhup.edu/~dsimanek/14/polaroid.htm
Modern three-dimensional movies project the footage from one camera in polarized light and use orthogonal polarization when projecting the footage from the other camera, the one that captured another perspective. The audience members wear polarizing glasses, with the axis of polarization for one eye orthogonal to that of the other eye.
Your team will use the principle of cross polarization to analyze materials with intrinsic polarizing properties. Some materials have atomic or molecular properties such that light is at least partially polarized when light passes through that substance. When the plane of oscillation of linearly polarized light is observed to be rotated after passing through materials with an asymmetry of their atomic or molecular structure.
Some materials will change the polarization of transmitted light when a stress or strain is applied. Placing such materials between two polarizers allows the amount of stress to be measured. Many transparent plastics objects that were formed by casting or with a pressing process have the property of rotating the polarization of transmitted light. The alignment of molecules is changed when under stress. The light passing through the plastic does not change in a way that is easily discernable to the naked eye; however, when the object is placed in a beam of polarized white light and viewed through another polarizer, the internal non-uniformities give rise to colors and patterns.
The effect that makes these colors appear is that the material has the ability to rotate the plane of polarization of the incident light beam. The degree to which the plane of polarization is rotated depends on the color of the light and the stress or characteristic of the material at any given point. The method is an important tool for determining critical stress points in a material.
If we polarize white light and pass it through sugar syrup, the direction of polarization of the light emerging from the syrup will be different for the different color components. If the light then passes through a second polarizer, its color changes with the orientation of the transmission axis of this polarizer. A sugar solution rotates the direction of polarization, extinction does not occur when the polarizers are crossed. Determine how much rotation is required to get maximum extinction. You should also note whether you need to give a clockwise or counter-clockwise rotation to the analyzing polarizer. To verify that the rotation is, say 20o clockwise rather than 160o counter-clockwise, you might vary the thickness of the solution. The rotation is due to an asymmetry in the corn syrup molecules. Fruit sugar and turpentine rotate in the opposite direction from sucrose.
Test your polarimeter with the provided clear plastic fork. The multiple colors are the result of different wavelengths of light. When you pull the tines of the fork apart, or squeeze them together, you will notice that the patterns change.
Use your polarimeter to observe the light transmitted through the provided square glass bottle. Compare what you observe to light passing through an empty bottle to the same bottle with tap water. Now pour some corn syrup into the bottle of water to create a dilute solution and compare what you observe to the previous situations.