Introduction: (Initial Observation)
While walking toward the pool, I noticed that it was much deeper then when I saw it empty a few days ago. As I got closer, it looked deeper and deeper again. I took a few steps back and fourth, I noticed that it just looked shallow when I stood away from it. Later in a side show I saw a boot with a small pool of water and one china plate at the bottom of it. You could pay a dollar and get a stun gun and shoot the plate in order to win something. Many were trying and they all failed to correctly aim the plate. The boot owner was basically using his knowledge of light refraction to make easy money.
Light refraction has also many industrial applications. In a tour from an oil company, I saw a device that can identify the density and the type of oil while the oil was passing trough a glass tube with a speed of about 35 miles per hour. That was called a refractometer. Knowledge of light is also used in magic and illusions. Magicians make an elephant disappear using the light reflection and mirrors. These all shows that light refraction, reflection and diffraction are important properties that demand more attention and study. One major question in my mind is that if these are the properties of light or the properties of objects and material?
If it be a property of light, we may be able to find some other lights that do not refract (bend), reflect, or diffract. Also if refraction, reflection, and diffraction are just the property of material, we may be able to find materials that act differently.
Also I want to know what other factors (if any) are involved.
This project is an opportunity to do some experiments and find some answers to these questions.
This is a large multi-part project. You may want to select only one of the parts. For example your project can be how does the frequency of the light beam affect it’s refraction?
Adult supervision is required
Find out about light properties. Read books, magazines or ask professionals who might know in order to learn about the effect of different material on light. Keep track of where you got your information from.
If you have ever half submerged a straight stick into water, you have probably noticed that the stick appears bent at the point it enters the water. This optical effect is due to refraction. As light passes from one transparent medium to another, it changes speed, and bends. How much this happens depends on the refractive index of the mediums and the angle between the light ray and the line perpendicular (normal) to the surface separating the two mediums. Each medium has a different refractive index. The angle between the light ray and the normal as it leaves a medium is called the angle of incidence. The angle between the light ray and the normal as it enters a medium is called the angle of refraction. Read more …
Refraction of light: The direction of light propagation can be changed at the boundary of two media having different densities. This property is called refraction, and is illustrated in the above figure for the boundary between air and water.
The apparent and actual positions of the fish differ because the direction of light propagation has been changed as light passes from the more dense water into the less dense air.
If we adopt the convention that the light passes from medium 1 into medium 2, the general rule is that the refraction is
- Away from the perpendicular if medium 2 is less dense than medium 1
- Toward the perpendicular if medium 2 is more dense than medium 1
Thus, in the above example the refraction is away from the perpendicular because air is less dense than water. Such effects form the basis of the refracting telescope, and of optical devices using lenses in general.
Diffraction of light: Diffraction is the bending of light as it passes the edge of an object. Because light is a wave, it has the capability to “bend around corners”. The intensity of light behind the barrier is not zero in the shadow region. Diffractive effects occur generally when a part of a light wave is cut off by an obstruction.
When a monochromatic light (light of a single wavelength) passes through a single slit, this is the pattern observed on the screen on the opposite side.
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 see what factors may affect the refraction, diffraction, and reflection of the light.
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.
Variables that may possibly affect the refraction, reflection, and the diffraction of the light are:
- Light frequency (remember light is a wave)
- Light intensity
- type of material exposed to the light
- Light angle
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 both the light frequency and the type of material can affect the the light refraction, reflection and diffraction. Light intensity however will have no affect on any of these properties.
My hypothesis is based on my observation of laser pointer light that can travel much more than a normal light without being diffracted by air molecules.
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.”
Light Refraction Experiments
This experiment is designed to show how does the light frequency affect the light refraction. For this experiment we will keep all other variables constant and only change the light frequency. As we already know, different color lights have different frequencies. So we need to test the refraction of different color lights. The frequency of visible light is referred to as color, and ranges from 430 trillion Hz, seen as red, to 750 trillion Hz, seen as violet.
For this experiment we pass a straight beam of white light trough a prism. White light consists of many different color lights. If each color refracts a different amount, the prism must be able to separate these colors. This experiment has been done many times and we have seen the results in books and we know that this will happen. If you want to repeat this experiment, following are some hints:
- Sun light gives the best result. You need a room that gets a lot of sun light trough a clean window. Then you cover the window with black construction paper and leave only one small hole or slot about 1 mm wide and 20 mm long. This makes the best light source for this experiment.
- Place a prism in the path of this light and keep a white paper behind that in a way that light passes trough the prism and gets to the paper.
- At this time you will see how different colors refract different amounts.
- What color refracts more? Picture below shows a similar quick experiment without having a dark room.
This experiment is designed to show how does the light intensity affect the light refraction. For this experiment we will keep all other variables constant and only change the light intensity.
We repeat the previous experiment with different light intensity and observe the location of the produced light spectrum. The intensity of sunlight can be reduced by passing trough a dark filter such as sunglasses. So simply hold a piece of dark glass in the path of sunlight before it gets to prism.
You can also change the light intensity by passing it trough two magnifier glasses. The reason that we use two magnifying glasses is that one will converge the parallel light beams of the sun and the other will make them parallel again. The distance between the magnifiers will affect the light intensity.
This experiment is designed to show how does the type of material affect the light refraction. For this experiment we will keep all other variables constant and only change the type of material.
For this project you will use a container and a laser pointer. Secure the laser pointer on the edge of the container with clamps or hot-melt glue in a way that it’s light ray have an angle of about 45 degree with the surface or bottom of the container.
Mark the point where the light hits the bottom of the container.
Then fill up the container with water. Mark the water level and mark the new position where the light hits the bottom of the container.
Remove the water and fill your container with some cooking oil. Make sure the oil level is the same is what your water level was before. Mark the new position of the light spot at the bottom of the container.
Note: Marking the position of light spot can be hard when the container is full of water or oil. I recommend to place a metal ruler at the bottom of the container and just make note of the position of light spot. In our experiment, we used a glass container, so we placed a measuring tape under the container.
Warning: Do not direct the laser light to your eyes or someone else’s eyes.
This experiment is designed to show how does the light angle affect the light refraction. For this experiment we will keep all other variables constant and only change the light angle.
Fill up your container with water and add a few drops of milk to make the water cloudy. This will make the light beam visible.
Hold the laser pointer to send a light beam in to the water from different angles. observe the displacement of rays or the amount of light break at different angles.
Smoke or water vapors in the room can make the light beams visible.
Referring to the above figure, the angle that your laser light makes with the line perpendicular to the water’s surface is called the angle of incidence and is represented by the angle a. The corresponding angle between the light beam inside the water and the perpendicular is called the angle of refraction and is represented by the angle b.
How does the angle of refraction change by changing the angle of incidence?
Following are images of some other experiments related to refraction.
Light Reflection Experiments
This experiment is designed to show how does the light frequency affect the light reflection. For this experiment we will keep all other variables constant and only change the light frequency or color.
Sun light is a good source of light for this experiment. Use a mirror to reflect the sunlight to a predetermined plain surface.
Sunlight consists of different color lights. If the reflection would be different for different color lights, the reflected light could be missing some colors or some colors may be reflected in a different position.
This experiment shows that the angle of incidence is equal to the angle of reflection for all colors.
In this photograph a convex lens is used to produce the parallel beam of light rays.
This experiment is designed to show how does the light intensity affect the light reflection. For this experiment we will keep all other variables constant and only change the light intensity.
This experiment is similar to the experiment 5. The only difference is that you will use a dark glass such as those used in sunglasses to reduce the light intensity to see if it causes any change in the angle of reflection.
This experiment is designed to show how does the type of material affect the light reflection. For this experiment we will keep all other variables constant and only change the reflecting surface. Mirror, glass and sheets of shiny metal such as steel, aluminum and copper can be used for this experiment.
Use a regular mirror to reflect a light beam of a laser pointer to a certain spot. then change the mirror and replace it with other shiny metals. Make sure that the reflecting surface will remain at the same position for different reflector material that you may try. Observe the location of light spot.
This experiment will show that the location of light spot does not change when you try different reflective material. The angle of incidence and the angle of reflection will remain the same.
This experiment is designed to show how does the light angle affect the light reflection. For this experiment we will keep all other variables constant and only change the light angle.
Us a regular mirror and a laser pointer. Direct the laser light beam to the mirror from different angles and observe the reflection angle. In this picture you see the light reflection from a small piece of copper.
In our experiment the angle of incidence and the angle of reflection remained the same for different reflective surfaces that we used.
For this experiment, hold the laser pointer in a way that the light beam touches the paper so you can see the light path.
Following are some other images from experiments related to reflection:
Light Diffraction Experiments
We classically think of light as always traveling in straight lines, but when light waves pass near a barrier they tend to bend around that barrier and become spread out. Diffraction of light occurs when a light wave passes by a corner or through an opening or slit that is physically the approximate size of, or even smaller than that light’s wavelength.
A very simple demonstration of diffraction can be conducted by holding your hand in front of a light source and slowly closing two fingers while observing the light transmitted between them. As the fingers approach each other and come very close together, you begin to see a series of dark lines parallel to the fingers. The parallel lines are actually diffraction patterns. This phenomenon can also occur when light is “bent” around particles that are on the same order of magnitude as the wavelength of the light.
A good example of this is the diffraction of sunlight by clouds that we often refer to as a silver lining, illustrated in the above picture with a beautiful sunset over the ocean.
We can often observe pastel shades of blue, pink, purple, and green in clouds that are generated when light is diffracted from water droplets in the clouds. The amount of diffraction depends on the wavelength of light, with shorter wavelengths being diffracted at a greater angle than longer ones (in effect, blue and violet light are diffracted at a higher angle than is red light). Click Here for a good demonstration of refraction.
This experiment is designed to show how does the light frequency affect the light diffraction. For this experiment we will keep all other variables constant and only change the light color. Remind you that each light color has a different frequency. The only high intensity pure lights that you can find are laser lights, so you can use two different laser lights with two different colors.
For this experiment you need a slit not wider than 0.2mm, but it can be smaller such as 0.04mm. You pass the laser light trough the slit and direct it to a screen such as a blank paper or a wall. Slits with different sizes are available for sale at laboratory supply stores, but we used a Caliper for our experiment and it worked. The jaws of caliper can get very close to each other to form a slit. Some have used two blades to make a slit, but blade are sharp and I don’t suggest it.
You may even ask an adult to use a blade or utility knife to cut a short slit in the middle of a black paper or aluminum foil. Any way the result of refraction can be seen in this picture.
After you secure the position of your slit and your screen and your light, you repeat the test with red laser light and blue or green laser light and compare the results.
Click here to see a graphical explanation of what happens in diffraction.
You must see that higher frequency lights such as blue and purple have a higher refraction than low frequency lights such as red. So you may conclude that the light frequency does affect the refraction.
This experiment is designed to show how does the light intensity affect the light diffraction. For this experiment we will keep all other variables constant and only change the intensity of our laser light.
After you set up the laser light, slit and the screen turn on the laser light and observe and mark the location of dots or lines on the screen. Leave the laser on for a while so it discharges it’s battery and the light intensity will reduce. Make observation every 5 or 10 minutes to see if reduction in light intensity has any affect on the position of light spots on the screen.
A laboratory setup that simplifies refraction experiments is shown in the following picture.
Materials and Equipment:
List of material can be extracted from the experiment section.
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.
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.
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.
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.
Refractive index of different material.
|Carbon Dioxide (gas)||1.000449|
|Emerald, Synth flux||1.561|
|Emerald, Synth hydro||1.568|
|Glass, Crown, Zinc||1.517|
|Glass, Flint, Dense||1.66|
|Glass, Flint, Heaviest||1.89|
|Glass, Flint, Heavy||1.65548|
|Glass, Flint, Lanthanum||1.80|
|Glass, Flint, Light||1.58038|
|Glass, Flint, Medium||1.62725|
|Water 35ºC (Room temp)||1.33157|