How do different surfaces affect the amount of sunlight reflected and absorbed?
Design a method of measuring how much sunshine is available each day.
Introduction: (Initial Observation)
In the summer time, when I was walking barefoot, I noticed that some surfaces are much warmer than others. I could easily stand and walk on a wooden board, but street asphalt was too hot to stand on it. I could also feel such differences by touching different objects.
This project is an opportunity to study the reasons that some surfaces absorb more heat from the sun.
Many factors may affect the absorption and reflection of sunlight. However, surface color is by far the most important one. Depending on your grade, you may not be required to study on any other factor but the surface color. In this project we have also considered one additional factor that are heat conductivity of the surface.
Information Gathering:
Find out about light and the way that it transmits energy. Read books, magazines or ask professionals who might know in order to learn about the factors that may cause a surface absorb more heat from the sunlight than others. Keep track of where you got your information from.
How do you measure the amount of absorbed or reflected sunlight?
The amount of light absorbed by a surface, will convert that light to heat energy. That results a temperature increase that can be measured by a thermometer. If the object reflects all the light, it should not get hot at all.
If the object absorbs part of the light, then it should get hot, but not as much as another object that absorbs all the light.
Scientists Take Big Steps to Measure Sunlight Reflected by Earth
Have you ever noticed that when the ground is covered with snow and the Sun shines, the edges of snow next to an exposed patch of earth or concrete melt faster? That’s because the white snow reflects the Sun’s radiation, while the darker earth absorbs it and heats up. Earth’s ability to reflect the Sun’s light, called albedo, is influenced by the color, type and texture of surfaces ranging from snow, vegetation and urban areas. In order for computer models to simulate and predict our weather and climate in a realistic way, it is vital to have accurate information about albedo for the whole planet.
What is a Sun photometer?
A Sun photometer (or sunphotometer) is a kind of light meter that measures the light from the Sun. Most Sun photometers measure sunlight at discrete colors or wavelengths. All Sun photometers measure only the sunlight arriving directly from the Sun and not the sunlight scattered from MOLECULES and AEROSOLS (or particles) in the sky. Therefore a Sun photometer must be pointed directly at the Sun.
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 find out the factors that affect heat absorption and heat reflection in a surface. We will also design a method to find out how much sunlight is available each day.
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.
Variables that may affect the absorption and reflection of the sunlight are:
- The color of the surface
- Heat conductivity of surface material
These variables are the independent variables for our project.
The dependent variable will then be the rate of heat absorption.
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 Dark colors will absorb more heat energy from the sunlight. White and reflective surfaces absorb very little heat. Higher specific heat and higher heat conductivity can also contribute to heat absorption.
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.”
Note: Following are just sample experiments to give you an idea and help you to design your own experiments. Experiment 1 for example can not be used for a reliable conclusion because two variables are changed at the same time. Using mirror as a test sample means that the color of sample and the material of the sample are both changed. If you want to follow a scientific method and change one variable at a time, you can use a glass mirror and two or three other colored glass pieces. You can find black, white and many other colors of glass. In this way all your test samples are glass and the only variable changed is the color. A glass with no color can be your control.
Experiment 1:
In this experiment we will test the effect of surface color on heat absorption.
Procedure:
- On a sunny day (as close to summer as possible) go outside and setup a space for your experiment. You need a piece of white paper, black paper, and a mirror. Place each piece of paper and mirror in a sunny spot as close to each other as possible. Leave the objects in the sun for 15-20 minutes. During this time, think about the following questions: “What’s happening to the paper and mirror right now? Is the sun hitting them? Is the same amount of sun hitting all of them? Is the sun bouncing off any of them? Are any of them reflecting the sunlight? Are they all reflecting the same amount? Do you think any of the surfaces are absorbing or soaking up the sunlight? If yes, are they all absorbing or soaking up the same amount of sunlight?
- Now take your journals to the test site. Touch each of the surfaces to determine which is the warmest and which is the coolest. Write hot, warm, cold in your journal under the pictures of the white paper, the black paper, and the mirror.
- Use the following possible questions to connect the ideas of reflectivity and absorption of the light to the heat. It is important that you understand that the mirror (and white paper somewhat) reflects the sunlight and absorbs little. Therefore it is not warmed by much light. The black paper however, reflects little and absorbs a lot of light. Since light energy converts to heat, the black paper gets the hottest.
- What did you notice the light does on the mirror? (bounces off, reflects)
Do you think the sunlight outside bounced off the mirror? (yes)
Did the mirror stay cool? (yes)
Did the mirror absorb or soak up much of the sunlight? (no)
Does the black paper reflect the sunlight? (no)
Does the black paper get hot? (yes)
Why did the black paper get hot? (absorbs or soaks up sunlight, light is heat)
Does the white paper get hot? (no) etc.
Experiment 2:
In this experiment we will test the effect of surface conductivity on heat absorption. As you may have already experienced, some material are a better conductive for heat than others. For example metals conduct heat better than wood.
Procedure:
- For this experiment you will need identical blocks of wood, iron, cardboard, plastic, aluminum, sheetrock or any other material that you can find. (Try to have at least 3 different type of material).
- Paint all surfaces with black paint and wait until all paints are dry prior to your experiment.
- On a sunny day select a sunny spot for your experiment and place your painted samples close to each other under the sun.
- After 60 minutes place a thermometer on each sample and record the temperature. (The accuracy of results depends on your thermometer)
- Touch all samples and see how do they feel!, Give a number to each sample from 0 for the coldest to 100 for the hottest. Record the results in your journal.
Another good experiment that you can design is using colored water. You can easily used food coloring or other water based colors to make colored waters. A few cups of colored water can easily show the effect of color in absorbing light. In this way a cup of water without color can be your control.
Experiment 3:
In this experiment we will measure how much sunlight is available each day.
Procedure:
There are different methods that can help you to measure the amount of sunlight on each day. Following are some suggestions that can help you to design your own experiment.
- Place a large bucket of water outdoor where it can get as much sunlight as possible. Paint it black (inside and outside) so it will absorb more sunlight. Fill it up with water and cover it with a sheet of glass or clear plastic. Measure the temperature of the water every morning before the sunrise and record the temperature again immediately after the sunset. The difference is the heat absorbed by the sunlight. Such a temperature increase can be a good representation for the amount of sunlight in that day. You cover the bucket with a clear glass or plastic to prevent air current or wind at the surface of the water. Air current and wind can cause evaporation of water and reduce the water temperature.
- A more modern method is using a photocell switch. It can be purchased from hardware stores and electrical stores. The switch can be tuned to close only under the sunlight with certain strength. This switch can be connected to an electrical timer to record the number of hours or minutes that the sun was hitting the switch. The exact design of such a set depends on the material that you may find in a local hardware store.
Materials and Equipment:
List of material depends on your final experiment design. Following is just a sample:
- 1 piece of black construction paper
- 1 piece of white construction paper
- 1 mirror
- white poster board
- woodblock
- Thermometer (If using a laboratory glass thermometer, place some lubricating grease between the thermometer bulb and the surface to increase heat conductivity)
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.
Calculations:
Description
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.
Your experiment will show that different surfaces absorb and reflect light and heat in different amounts. Write the results showing what surfaces absorb or reflect more sunlight.
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.
