Author: Sandy Van Natta
A radiometer is made from a glass bulb from which much of the air has been removed. Inside the bulb is a low friction spindle and a rotor with several lightweight metal vanes spaced equally around the axis. When the bulb is exposed to certain energy sources, the rotor turns.
This module allows participants to investigate the motion of the rotor by designing their own experiments and drawing their own conclusions based upon their observations and data. They will then be asked to identify the energy conversions taking place that allow potential energy to be converted into the kinetic energy of the turning rotor.
This module also leads participants through the process of designing an experiment so that they can direct their own students to do the same. As a final part of this module, teachers develop a plan to implement what they have learned in their classrooms.
One radiometer per group (or Crookes Radiometer) - available from most science supply houses for about $10.00 a piece
Have as much of the following available for testing as possible:
*Note: only one or two of the above items are needed for testing since each group will be testing different variables
This stage focuses the participant's attention on a topic and poses a problem for the participant to explore in the next phase of the learning cycle.
Assessment: This is an on-going process throughout the learning cycle. The participants should respond orally in the Engage stage as well as throughout the cycle. Try to encourage all participants to take part in your discussion.
Assessment: Monitor the groups' work to be sure that they are recording data, discussing findings, and answering the posed problem.
In this phase, participants use the data they have collected, whether observational or numerical, to draw conclusions relating to the motion of the rotor. However, you may first want to ask the participants about the steps they just went through to design and set up an experiment. (How to write a question, how to identify variables, how to write a procedure, etc.)
You may now wish to ask the participants what factors they discovered affected the motion of the rotor.
At this point you may want to discuss the history of the rotor. A brief background is given in the Explanation of the Science section.
Assessment: During the Explanation phase, the participants can be evaluated by being asked questions that assess the participant's comprehension of vocabulary and concepts. Ask participants how they would relate this activity to the teaching of energy conversions in their own classrooms. Ask them how the use of inquiry in this activity compares to other methods of instruction used in their classrooms. Encourage all participants to participate in the discussion.
Allow the participants to design additional experiments with the radiometer using the materials at hand or other materials they might have in their classrooms if additional questions are raised during your discussion. Have them suggest other ways of using inquiry to teach energy conversions to their own students. Give time for participants to complete the lesson implementation sheet as a first step to moving toward classroom implementation.
Assessment: Check the lesson implementation plans for faithfulness to the lesson just experienced. If possible, visit the participants' classes for onsite assessment.
Every facet of our lives involves energy and energy conversions. For example, chemical energy in the food we consume is converted into the energy needed by our bodies to move (kinetic energy) as well as keep our bodies warm (thermal energy). Since energy is constantly changing from one form to another, we often take these conversions for granted.
The radiometer is a simple devise that allows the participants to determine the effect of different types of energy (thermal, radiant, magnetic, etc.) on the motion of the rotor. Testable questions can be asked, simple experiments performed, observations made, and conclusions drawn in a relatively short amount of time. Participants will have fun conducting simple experiments while, at the same time, identifying and discussing excellent examples of energy conversions. This is an excellent inquiry activity that allows the participants to determine the path of their own learning experiences. They can then use the ideas presented here as a model for inquiry lessons in their own classrooms.
Science as Inquiry:
Content Standard A: As a result of activities in grades 5 – 8, and 9-12, all students should develop:
Physical Science Standards:
Content Standard B: as a result of their activities in grades 5-8, all students should develop an understanding of:
Content Standard B: as a result of their activities in grades 9-12, all students should develop an understanding of:
Standard A: Professional development for teachers of science requires learning essential science content through the perspectives and methods of inquiry. Science learning experiences for teachers must:
Standard B: Professional development for teachers of science requires integrating knowledge of science, learning, pedagogy, and students; it also requires applying that knowledge to science teaching. Learning experiences for teachers of science must use inquiry, reflection, interpretation of research, modeling and guided practice to build understanding and skill in science teaching.
This activity should take about 45 minutes to complete
Purchase the radiometers in advance unless they are already available in your science department. Assemble the "testing" materials (lights, magnets, etc.) in a tub to set out in the front of your classroom
Handle the radiometers with care since they are made of glass. No other special precautions are needed.
Have participants suggest ways of teaching energy conversions in their own classrooms.
The radiometer was invented in 1873 by the chemist Sir William Crookes. The radiometer is made from a glass bulb from which much of the air has been removed to produce a partial vacuum. A rotor with usually four lightweight metal vanes spaced equally around the axis sits on top of a low friction spindle. The vanes are either polished or white on one side and black on the other. When exposed to light, either artificial or natural, or infrared radiation, the vanes turn. Even the heat from a nearby hand can be enough to cause the rotor to turn. The more intense the energy source, the faster the spinning. The dark sides retreat from the radiation source and the light sides advance. Cooling the radiometer causes rotation in the opposite direction.
Crookes first believed that light radiation pressure on the black vanes was turning the rotor around just like water in a mill. However, there was a problem with this explanation. Light falling on the black side should be absorbed and light falling on the white side should be reflected. The net result would be twice as much radiation on the white side as the black. If that were the case, the rotor was spinning the wrong way.
So what causes the rotor to spin? Since so little gas remain inside the radiometer compared to the trillions of air particles outside the radiometer, the air remaining inside can move about more freely. The dark side of the rotor vanes absorb more energy than the light side and a temperature difference develops between the vanes. The difference between the temperature of the warmer black side and the cooler white side causes the gases to creep along the surface of the vanes. The faster gases from the black side strike the edges of the vanes at an angle with more force than the molecules from the cold side. This causes the radiometer to spin. If you cool the glass quickly in the absence of a strong light source by placing ice on the glass, it turns backwards. This is because the black sides give off more heat and cool more quickly than the lighter sides.
None available for this module.
Have participants describe the energy conversions witnessed in daily life such as a light bulb attached to a battery, falling water turning a paddle wheel, or sunlight allowing plants to grow. Have them relate the energy conversions to the Law of Conservation of Energy.
When dividing participants into groups, try to be sensitive to gender, ethnic and religious backgrounds. Try to make groups as heterogeneous as possible.
None available for this module.
With thanks to educators affiliated with the University of Iowa whose creative ideas in a teacher workshop inspired this module
Crookes radiometer, http://en.wikipedia.org/wiki/Crookes_radiometer