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# Light

## Light

### Introduction: (Initial Observation)

When white light is directed into a prism, a pattern of brilliant colors come out the other side. But how does this work? And does it help explain color and light?

Many other properties or applications of light can be researched into this project.

Some of the sub titles that you can choose to be the main focus of your research about light are as follows:

• Compare the intensity of light from different light sources.
To do this you may need to purchase a light meter or build one. You then expose your light meter to different sources of light and record the results.
• How does color affect the absorption and reflection of light?
Get a few glass thermometers and cover the bulb of thermometers with different color paints. Let them dry and then place them under the sunlight and record the temperatures after about 5 minutes.
• How does the intensity of light changes by distance?
Record the intensity of light at different distances from a light source. Record the results and draw a graph.
• How does a surface condition affect the light reflection?
Get a shiny piece of steel or aluminum and test the light reflection on that using a laser pointer. Then scratch the surface using a sand paper to see how the roughness of the surface affect the reflection of the light.
• How does a prism analyze the light?
Isolate a narrow beam of sunlight and place a prism on its path until you see a color spectrum. Which colors refract more?
• What material are transparent, translucent or opaque?
Use a flashlight or laser pointer in a dark room to see what material are transparent, what material are translucent and what material are opaque.
• Is there such a thing as invisible light? (Experiment 2 in this page)
Use a beam of sunlight and a prism to form a spectrum of different color lights. Measure the temperature of each area and then measure the temperature of area right passed red that has no light. Excess heat in that area is an indication of an invisible radiation or invisible light known as infra red.
• Which color light is the warmest? (Experiment 1 in this page)
Use a beam of sunlight and a prism to form a spectrum of different color lights. Measure the temperature of each color light and record the results.

Although it is a good choice to have a good light source for light related projects, you can often use sun light instead. Experiments can be designed to be simple and material needed for experiments can simply be purchased locally or ordered via the internet.

Dear

This project guide contains information that you need in order to start your project. If you have any questions or need more support about this project, click on the “Ask Question” button on the top of this page to send me a message.

If you are new in doing science project, click on “How to Start” in the main page. There you will find helpful links that describe different types of science projects, scientific method, variables, hypothesis, graph, abstract and all other general basics that you need to know.

What is Light?

Light is an amazing phenomena with properties unique to itself. Many scientists in the past have studied light and have used it as a valuable tool for their research. Even today light is one of the most important research subjects for scientists.

Light is the type of energy that our vision cells are sensitive to, that is why we can see where there is a light. Every substance in the world emits a special light when it is heated at high temperatures. With these special lights, scientists can identify the type of substances. With the light coming from the sun and other stars, scientists know what chemicals are available in each star.

Light is a wave of magnetic field. Many other types of radiation are also waves of magnetic fields. For example radio waves, Micro waves, Infra red, Ultra Violet and X-ray are all electromagnetic waves. The reason that we can see light and we can not see other types of electromagnetic waves is that our vision cells are not sensitive to those waves. The difference between these waves is their frequency.

What is frequency?

If you hold a magnet in your hand and start to shake it or wave it at a speed of 3 times per second, then you are producing a magnetic wave with frequency of 3 per second or 3 Hz. You may use a different method to vibrate your magnet at a rate of 20 times per second; then you are producing a magnetic wave with frequency of 20 Hz. Higher frequencies can be made using and electromagnet.

The electricity that we use at home is an alternative current at 50 Hz. In other words a flow of electrons are moving back and forth in wire at the rate of 50 times per second. If you connect such electricity to an electromagnet, it will create an electromagnetic waves with frequency of 50Hz. Radio frequencies are usually in the range of million Hz or Mega Hertz. For example a radio station may be broadcasting at 99 MHz (Read 99 Mega Hertz. Mega means million).

The frequency of visible light ranges from 430 trillion Hz, seen as red, to 750 trillion Hz, seen as violet. As you see different color lights have different frequencies.

White light is a combination of all different light frequencies.

### Information Gathering:

Find out about light and its properties. Read books, magazines or ask professionals who might know in order to learn about different color lights and their differences. Keep track of where you got your information from.
Click here to read some interesting facts about light, which is an electro magnetic wave. Skip any part that you don’t understand. The following is a simplified/ modified version as a quick reference.

Scientist say light is an electromagnetic wave! But, what is an electromagnetic wave? What does it mean.

Magnetism can be static like a refrigerator magnet. But when you shake or vibrate a magnet, you are creating a moving magnetic field or electromagnetic wave. Another way of making an electromagnetic wave is sending a changing (alternative) electric current into a coil of wire. The most common electromagnetic waves that we know about are radio waves. James Clerk Maxwell and Heinrich Hertz are two scientists who studied how electromagnetic waves are formed and how fast they travel.

When you listen to the radio, watch TV, or cook dinner in a microwave oven, you are using electromagnetic waves.

Radio waves, television waves, and microwaves are all types of electromagnetic waves. They only differ from each other in wavelength. Wavelength is the distance between one wave crest to the next.

Waves in the electromagnetic spectrum vary in size from very long radio waves the size of buildings, to very short gamma-rays smaller than the size of the nucleus of an atom.

Did you know that electromagnetic waves can not only be described by their wavelength, but also by their energy and frequency? All three of these things are related to each other mathematically. This means that it is correct to talk about the energy of an X-ray or the wavelength of a microwave or the frequency of a radio wave.

The electromagnetic spectrum includes, from longest wavelength to shortest: radio waves, microwaves, infrared, optical, ultraviolet, X-rays, and gamma-rays.

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## Visible Light Waves

Visible light waves are the only electromagnetic waves we can see. We see these waves as the colors of the rainbow. Each color has a different wavelength. Red has the longest wavelength and violet has the shortest wavelength. When all the waves are seen together, they make white light.
When white light shines through a prism or through water vapor like this rainbow, the white light is broken apart into the colors of the visible light spectrum.

How do we “see” using Visible Light?

Cones in our eyes are receivers for these tiny visible light waves. The Sun is a natural source for visible light waves and our eyes see the reflection of this sunlight off the objects around us.
The color of an object that we see is the color of light reflected. All other colors are absorbed.

Light bulbs are another source of visible light waves.

### 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.

When we feel cold, we walk to a sunny space to use the heat of sunlight. Now that we know sunlight is a combination of different color lights, it is good to know which of these color lights carry more heat energy or which color light is warmer.

Question: How do different color lights vary in the amount of heat energy that they carry? Which color light is the warmest?

### 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 (also known as manipulated variable) is the color of the light.

Dependent variable (also known as responding variable) is the amount of heat carried by each color 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. Following is a sample hypothesis:

I think red color is the warmest light. My hypothesis is based on my observation of some electric heaters that have a heat lamp as the source of heat and the heat lamps are red.

### 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 1:

Determine which color light is the warmest.

Introduction: In the year 1800, Sir William Herschel performed this experiment and it led to discovery of an invisible light called infrared. Herschel passed sunlight through a prism. As sunlight passes through the prism, the prism divides it into a rainbow of colors called a spectrum. A spectrum contains all of the colors which make up sunlight. Herschel was interested in measuring the amount of heat in each color. To do this he used thermometers with blackened bulbs and measured the temperature of the different colors of the spectrum. He noticed that the temperature increased from the blue to the red part of the spectrum. Then he placed a thermometer just past the red part of the spectrum in a region where there was no visible light and found that the temperature there was even higher. Herschel realized that there must be another type of light which we cannot see in this region. This light was called infrared. Here you repeat William Herschel’s experiment to see how different are the temperatures of different color lights.

Procedure:

You need an equilateral glass prism, 3 alcohol thermometers, scotch tape, a white piece of paper and a south facing window sill or a box. The cost of the prism we used was about \$7.50 (from MiniScience.com) and the thermometers were 75 cents a piece (from a hardware store). You will need to blacken the bulbs of the thermometers so it will absorb the heat energy from light waves. To do this you can insert the bulb of thermometers in black paint and then let it dry. Alternatively you may mask the thermometers with masking tape exposing only the bulbs and then spray paint the bulbs with a flat black paint.

In the above image you can see how to set up this experiment for use outdoors. Place a white piece of paper at the bottom of a cardboard so the bottom of box does not get so hot.
Rotate the prism until a good wide spectrum appears on the white paper at the bottom of the box and then tape the prism into place. To get a good spectrum you may have to tilt the box up on the prism end by placing a rock under it.

First check the temperature of the thermometers away from the spectrum in the shaded area of the box. The above image shows the temperature before the thermometers are placed in the spectrum. All 3 thermometers must read the same temperature.

If you only have one thermometer, place the thermometer bulb in blue section of spectrum, hold it there for about one minute and then read the temperature while the the blackened bulb of the thermometer is still in the blue section. Record the temperature. Repeat this with green section, yellow section and red sections of spectrum.

Record your results in a table like this:

 Color Light Temperature Blue Green Yellow Red

If you have three or more thermometers, you may place them or tape them all at the same time at the bottom of the box in a way that each thermometer measures the temperature of a different color.

It takes a few minutes for the temperatures to reach their final value. Within 1 minute you can already see a difference in temperature. The differences between the 3 temperature readings continue to grow larger until the final temperatures are reached.

You may want to use a larger cardboard to make shade over your experiment setup. In this case you must cut an opening not larger than your prism so the sunlight will get to the prism while all other areas are still in shade.

Finally use your results table to draw a graph.

This project require sunlight and is really good for hot sunny days. In a cold windy day, all the heat of sunlight will be immediately removed by the wind. The solution to that is covering the box with glass or clear plastic.

### Experiment 2:

Is there such a thing as invisible light?

Procedure:

Repeat the previous experiment, but this time also measure the temperature immediately before the purple and immediately after the red light. These areas have no visible light; however their temperature may indicate presence of invisible radiations separated from the sunlight by the prism. Record your results in a table like this:

 Color Light Temperature Ultra Violet Blue Green Yellow Red Infra red

Note: Presence of Ultraviolet light may not be observed in this way because UV does not create noticeable amounts of heat.

### Materials and Equipment:

Complete list of material can be extracted from the experiment section.

• Prism (See samples of prisms at MiniScience.com)
• Thermometer (See samples of thermometers at MiniScience.com)

### 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.

Sample Results:

The thermometer in the blue part of the spectrum shows the lowest reading which is not much higher than shade temperature. The yellow part of the spectrum is showing a much higher temperature than the blue. The thermometer on the right, which is in the dark region just past the red, is showing the highest temperature of all 3 regions.

 Color Light Temperature Blue 80º F Green 81º F Yellow 83º F Red 85º F Infra red 86º F

Notes:

1. The differences between the temperatures of the colors of the spectrum vary with the width of the spectrum, which depends on time of day, and the distance from the prism, which is proportional to the height of your box. In all cases the trend of temperature increasing from blue to infrared should still show up.
2. All the wavelengths farther than the infrared are compressed to a small region just beyond the red (see Reconciling The Herschel Experiment). For typical box depths of 0.3 m, no solar wavelengths are beyond 0.4 cm from the end of the red, so the “infrared” thermometer must be placed immediately next to the end of the observed spectrum.
3. If you can arrange to have the prism more distant from the projected spectrum, the wavelengths will be spread out farther, giving more room to explore the infrared. However, the difference in the thermometer readings will be smaller since they will intercept less energy.

Herschel’s experiment was important not only because it led to the discovery of infrared light, but also because it was the first time that someone showed that there were forms of light that we cannot see with our eyes. As we now know, there are many other types of light that we cannot see and the visible colors are only a very small part of the entire range of light which we call the electromagnetic spectrum.

### Calculations:

No calculation is required for this project.

### Summery 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.