THE STUDY OF HOW MUCH LIGHT IS REFLECTED OFF OF EVERYDAY HOUSEHOLD OBJECTS

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1 THE STUDY OF HOW MUCH LIGHT IS REFLECTED OFF OF EVERYDAY HOUSEHOLD OBJECTS Joshua Pullen Cary Academy ABSTRACT The purpose of these experiments was to discover what materials reflected the most light and how much light passed through different objects and liquids. Objects reflect light because the light will strike an object and then bounce off at an angle equal to the angle at which it struck. A mirror, aluminum foil, and a piece of paper were placed on a table in a dark room with the flashlight held 6 in away and the light probe was held 6 in away at an equal angle. It was found that the mirror reflected the most light (238 LUX), the paper reflected the least light (8.33 LUX), and the aluminum reflected the second most light (46.66 LUX). These results were found because a mirror is a smooth, shiny reflective surface, aluminum foil is a wrinkly, shiny surface and paper is a rough, dull surface. INTRODUCTION Light has many different qualities that allow us to see. Reflection is when a ray of light strikes a smooth surface and bounces off at the same angle that it struck (figure 1). If a surface is shinier, it can reflect more light, and if it is dull, it will reflect less. An incoming ray of light has electrons that will absorb energy, but will not pass it on to different atoms. They will slightly vibrate and then they will bounce back, with the same frequency of the incoming wave. The law of reflection states that an angle where the ray strikes the surface (called the angle of incidence) is always equal to the angle in which the light beam leaves it, so when the electrons bounce off they come right back to the object in which they came from. This happens very quickly, so it looks like the reflection hasn t

2 moved at all. If the surface isn t smooth, light will scatter in all directions. This is why people can read words on paper from most directions. Light moves at approximately 300,000 km/sec in a straight line. Light slows down a little when it passes through transparent matter like air, water, and glass. Refraction occurs when light travels through one transparent matter to another, like light going through air into water. When this happens, the speed of the light can change and the light ray can bend. That is why some things appear closer, bigger, or bent in water. Absorption of light is when light strikes an object and it doesn t all bounce off, but just stays there. The reason that some objects are dark is because they absorb light, and if the light doesn t bounce back to our eyes, people can t see it very well. Figure 1- reflection of light The reason that humans and animals can see is because there is light. If there was not light, there would not be a sense of sight. Light is measured in different ways. Light is measured in energy (W), and in brightness, or illumination (lux). If people stand very close to a light, it may seem bright, but if people move father away, it will seem to dim or people may not even see it. Photons are small packets of energy that make up light. Photons make up light waves, which can travel in rays. Color originates in light. Our eyes make sunlight appear colorless, but really, it is all of the colors. Think of when after it rains really hard, the sun comes out and there is a rainbow. The mist from the rain splits up the light into the colors that people see in the

3 rainbow. The colors from the rainbow just make up a small part of the giant spectrum of energy, which is electromagnetic radiation. There are two types of electromagnetic radiation. One type is visible light. Visible light comes from things like lamps, and it is light that people can see. There are also radio waves, like the ones that come from radio stations. People cannot see radio waves. Electromagnetic radiation can be described as a stream of photons. Photons are particles that have no mass that each travel in waves at the speed of light. Every photon contains a certain amount of energy, and all electromagnetic radiation consists of these photons. A previous experiment was done by Aly Halferty to find out if it was true that wearing black clothes attracted more sunlight and made people hotter but wearing white made people cooler. She tested pink, green, black, and white shirts and discovered that white reflected the most light and black absorbed the light. The flashlight was held 50 cm away from the shirt, and the light probe was held 25 cm away from the shirt. The white shirt reflected 55.5 LUX, and the black shirt only reflected 12.3 LUX. MATERIALS AND METHOD In this experiment, a light sensor, a flashlight, paper, a mirror, aluminum foil, a computer, a beaker, an eye dropper, measuring spoons, salt, and food coloring was used. In the first experiment, light was shined off of a mirror, aluminum foil, and paper in a dark room (figure 2). The flashlight was held 6 in away from the reflecting surface, and the light probe was held 6 in away at an equal angle from the flashlight. Each surface was measured 3 times and an average was taken.

4 Figure 2: an example of the first experiment In the first follow up experiment, light was shined off of a dry mirror, and a mirror with 0.5, 1, and 1.5 ml of water added. The flashlight was held 6 in away from the mirror, and the light probe was held 6 in away at an equal angle to the flashlight. Each amount of water was done three times and an average was taken. In the second follow up experiment, light was shined through 250 ml of water in a beaker with 1, 2, 3, 4, 5, and 6 teaspoons of salt added. The flashlight was held 2 in away from the beaker on one side, and the light probe was held 2 in from the other side of the beaker. Each amount of salt was done three times and an average was taken. In the third follow up experiment, 10 drops of red, green, blue, and yellow food coloring were dropped into 250 ml of water. The flashlight was held 2 in away from the beaker on one side, and the light probe was held 2 in from the other side of the beaker. Each color was done three times and an average was taken. RESULTS AND DISCUSSION In the first experiment, different objects were tested to find out which one reflected the most light. The flashlight that was used had a brightness of 770 LUX. It was discovered that the mirror reflected the most light, second was aluminum foil, and paper reflected the least. The mirror reflected an average of 238 LUX. The aluminum foil reflected about LUX, and the paper reflected only 8.33 LUX (figure 3). This happened because

5 light reflected (lux) mirrors are smooth, shiny surfaces that are easy for light to reflect off of. Aluminum foil is shiny, but bends a lot and makes the light go everywhere. Paper is just a slightly rough surface that is not very shiny, but scatters the light all around normal light paper aluminum foil mirror reflective surface Figure 3. The amount of light different objects reflect In the first follow up experiment, light was reflected off of a dry mirror, and a mirror with 0.5, 1, and 1.5 ml of water added. The dry mirror reflected the most light, followed by 0.5 ml, 1 ml, and with the least light, 1.5 ml. The dry mirror reflected LUX, and 0.5 ml of water added reflected LUX. The mirror with 1 ml of water reflected LUX, and the mirror with 1.5 ml of water only reflected 11 LUX (figure 4). These results were found because with more water, there was a greater angle of refraction, which lost some of the light, only reflecting back a smaller portion of the light. The dry mirror had no refraction, so most of the light was reflected.

6 light reflected (lux) Amount of water (ml) Figure 4. The amount of light a wet mirror reflects. In the second follow up experiment, different amounts of salt were added to 250 ml of water. Normal water without salt added let the most light through, and LUX passed through the water. After that, the results were in order. With 1 tsp. of salt added let 118 LUX through, 2 tsp. let 95 LUX through, 3 tsp. let LUX through, 4 tsp. let LUX through, 5 tsp. of salt added let LUX through, and 6 tsp. of salt added let LUX through (figure 5). This happened because with more salt added to the water, the water started to absorb the salt and it became very foggy after 3 tsp., so the light barely passed through the water.

7 light passed through (lux) amount of salt (tsp) Figure 5. The amount of light that passes through water with different amounts of salt added. In the third follow up experiment, 10 drops of different colored food coloring were dropped into 250 ml of water. The water without any food coloring in it let the most light pass through. Normal water allowed 238 LUX to pass through. The yellow food coloring allowed 132 LUX to pass through, red allowed 78 LUX to pass through, green allowed 22 LUX to pass through, and blue food coloring allowed only 15 LUX to pass through (figure 6). This happened because the blue was very dark and quickly took over the water, making it almost impossible to see through. The yellow only slightly tinted the water, so it was easy to see through.

8 light passed through (lux) clear red yellow green blue color of the water Figure 6. The amount of light that passes through different colored water. CONCLUSION The most important information in this experiment was that the mirror reflected the most light, and the paper reflected the least. The hypothesis was correct because it was predicted that the mirror would reflect the most light and that the paper would reflect the least. A future follow up experiment that could be done would be to reflect light off of different slightly clear surfaces or to shine light through sunglasses to find out how much they help. CITATIONS Halferty, Aly. The Study of How Much Light Reflects off of Different Colored Shirts. Cary Academy, Print. Harris, William, and Craig Freudenrich, Ph.D.. "How Light Works" 10 July HowStuffWorks.com. < 14 February Lewis, Peter. Light and sound. Tucson, Brown Bear Books: Print.

9 "Light." Britannica Elementary Encyclopedia. Encyclopædia Britannica Online School Edition. Encyclopædia Britannica, Inc., Web. 12 Jan Light, Douglas. The Senses. Philadelphia, Chelsea House: Print. Trethewey, Ken. "How Light and Brightness is Measured." How lighthouses work. N.p., N.d. Web. 14 Feb