Introduction: (Initial Observation)
I clearly remember the shiny reflectors on the sides of dark roads. They are a great contribution to the safety and comfort of driving at night. Some of these reflectors can be seen from about a quarter mile away.
I have always wondered how these pieces reflect so much light that we can see them from every spot in the road.
One night while walking on the road side, I noticed that the reflectors do not shine any more. Even though the cars were passing by with headlights on, none of the reflectors had the continuous shine and visibility that I was used to seeing.
Soon I started to examine reflectors on cars, bicycles, and standalone triangle reflectors. Deep inside each reflector I could see geometric shapes (often triangles). But what do they mean?
I took a reflector in the dark. It had no light. In other words, it was not phosphorescent that stores light energy.
In this project I will investigate reflectors and how they work.
Information Gathering:
Find out about reflectors and how they work. Read books, magazines, or ask professionals who might know in order to learn about the structure of a reflector, its uses, and how it can be made. Keep track of where you got your information from.
Following are samples of information that you may find:
Reflectors used on the road sides are a matrix of many small corner reflectors, also known as universal reflectors.
Each universal reflector is made of two or more mirrors placed at an angle that makes them reflect any light beam back to the same direction as it originated.
Universal reflectors have many uses. One common use is as a safety marker to show the road sides and traffic lanes.
Universal reflectors are also used to reflect laser beams and radar waves.
corner reflector:
1. A reflector consisting of three mutually perpendicular intersecting conducting flat surfaces, which returns a reflected electromagnetic wave to its point of origin. (188) Note: Such reflectors are often used as radar targets. 2.A directional antenna using two mutually intersecting conducting flat surfaces. 3. A device, normally consisting of three metallic surfaces or screens perpendicular to one another, designed to act as a radar target or marker. [JP1] 4. In radar interpretation, an object that, by means of multiple reflections from smooth surfaces, produces a radar return of greater magnitude than might be expected from the physical size of the object. [JP1] 5. A passive optical mirror, that consists of three mutually perpendicular flat, intersecting reflecting surfaces, which returns an incident light beam in the opposite direction.
Consider three identical square planar mirrors that are glued together to form three adjacent sides of a cube meeting at a corner, with the mirrored sides all facing towards each other. Show that these mirrors act as a universal reflector that sends light back to its source: any light beam entering this arrangement of mirrors will leave parallel and opposite to its original direction.
If you look into such a corner reflector, what kind of image will you see of your face?
Note: Such corner reflectors were left on the surface of the moon by Apollo astronauts and were used in ranging experiments, in which laser beams from an observatory on Earth were bounced off the surface of the Moon and returned to the observatory, with the time of transit being measured. This enabled the distance from the Earth to the Moon to be measured with high accuracy, which has been useful in testing the theory of general relativity and also for investigating the geology and origin of the Moon.
Radar reflectors are a passive means of jamming radar systems. These may be corner, pyramid, spherical, or dipole reflectors that are designed to reflect radar energy back to the sending radars. When suspended in pairs along a road or scattered in an area, corner reflectors create a bright return on a radar scope that masks any activity along the road or within the area (fig. 7).12 The sensor will indicate that something is present but will give no indication of its nature. This makes it difficult to accurately detect movement along the road or activity in the area, thus adding an element of confusion and possibly concealing any activities. Corner reflectors may be issued or produced in the field from wood and metallic foil. During the mid-1970s, each Soviet motor rifle battalion was provided 30 Corner reflectors.
Radar reflectors may also be used for imitation and simulation. Corner reflectors placed inside or beside dummy tanks will imitate the radar image of a tank.13 Radar reflectors may be placed on motorcycles that travel up and down roads to simulate heavy traffic
This is a single corner reflector set up on a piece of re-bar that has been pounded into the cinders. The painted board helps the EDM operator to find the reflector since he or she is often looking for it over distances of a few kilometers. This type of low-tech reflector is relatively expendable and is usually left out in areas where eruptions are possible. For more precise measurements, clusters of 3, 6, or 9 reflectors are used, but they are only installed while the measurements are being made. Source…
Universal reflectors are not just for reflecting light. They are also used for reflecting radar and other electromagnetic waves.
Image Source…
The picture on the left shows a universal reflector made of mirrors.
Picture in the right is a universal reflector used in the roads to mark the traffic lanes.
Radar Reflectors
A radar search for craft built of materials other than steel or aluminum is often ineffective unless some form of radar reflector is displayed.
Radar echoes from such craft are variable, the detection range always being relatively short in relation to the size of the vessel. Small metal targets have been detected at greater ranges than the craft themselves.
A radar reflector greatly improves the chances of detection and success in a radar search. It is desirable, therefore, that all vessels carry some form of reflector. It should be carried on the mast or at the highest practicable position on the vessel to give maximum detectable range.
A radar reflector must be of metal (preferably aluminum) construction and designed to reflect any radar pulse intercepted. This can be efficiently done by a corner reflector consisting of three metal plates placed at right angles to each other. Eight corners placed around a common center gives full reflection in azimuth and elevation.
If such a reflector is not available, a more simple type can be used which will give varying degrees of reflection. A design consisting of two slotted metal plates set at right angles, or a flat metal plate at least 300 mm square (but preferably larger) which can be hoisted as high on the vessel as practicable are alternatives.
If no properly constructed reflector is carried, it may help searchers using radar if the distressed vessel hoists any available metal objects as high above the hull as practicable in the circumstances. Petrol cans, cooking utensils or any other metal objects will serve.
Corner reflector & Simple practical reflector
Question/ Purpose:
What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.
The purpose of this project is to design and construct a universal reflector. I also like to know if I can see myself in a universal reflector from different angles.
Identify Variables:
When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.
Independent variable is the angle of light beam.
Dependent variable is the angle of reflected light.
Hypothesis:
Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis.
My hypothesis is that you can see your face in a universal reflector from different angles.
Experiment Design:
Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”
Experiment: (Make a Universal Reflector)
Introduction: Two hinged mirrors create a kaleidoscope that shows multiple images of an object. The number of images depends on the angle between the mirrors. When you set the hinged mirrors on top of a third mirror, you create a reflector that always sends light back in the direction from which it came.
Material:
1.Three 6 x 6 inch (15 x 15 cm) mirrors. Plastic mirrors are best, since there is less danger of breaking the mirror or cutting your fingers. Plastic mirrors are available at plastics supply stores and can easily be cut to any size. Glass mirror tiles are readily available but are not as safe.
2.Duct tape.
3.A piece of light cardboard (such as a manila file folder).
4.Adult help.
If you don’t have access to a local source for mirrors, you may order them online from www.SchoolOrders.com. SchoolOrders.com is an online store for science supplies needed by schools and students. Following are the part numbers:
Plastic Mirrors: # 3240
Glass Mirrors: # 3366
Results of Experiment (Observation):
Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.
Following are some sample results:
When you put an object between the two hinged mirrors, light from the object bounces back and forth between the mirrors before it reaches your eyes. An image is formed each time the light bounces off a mirror. The number of images that you see in the mirrors depends on the angle that the mirrors form. As you make the angle between the mirrors smaller, the light bounces back and forth more times, and you see more images.
The illustration below shows how an image is formed in the corner of two mirrors at 90 degrees. Light rays bounce off each mirror at the same angle that they hit the mirror: Physicists say that the angle of reflection is equal to the angle of incidence. Mirrors at other angles behave similarly, but the ray diagrams may get more complex.
The inside corner of a corner reflector (where the three mirrors meet) sends light back parallel to its original path. If you pointed a thin beam of laser light right near the corner, the beam would bounce from mirror to mirror and then exit parallel to the entering beam. Light from the center of your eye bounces straight back to the center of your eye, so the image of your eye seems to be centered in the corner made by the mirrors.
In a corner reflector, multiple reflections reverse the image and invert it.
Calculations:
Calculation of the number of images based on the angle between two mirrors is described in the experiment section.
Summary of Results:
Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.
It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.
Conclusion:
Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.
Related Questions & Answers:
What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.
Possible Errors:
If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.
If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.
References:
List of References
http://sunearth.gsfc.nasa.gov/eclipse/SEhelp/ApolloLaser.html
