## Preparation

The most important step in the process of the unit development is to built a skeleton of the material to be presented and the activities to be used in class. This is the logical format of the electromagnetic radiation unit that would be the most effective.

```----------------------------------------------------------
No.  Learning Material    Type of Activity     Experiment

1.   Properties and       -Introduction of    -Ripple tank
characteristics       new material        experiments
of electromagnetic   -Discussion
waves                -Problem solving

2.   Electromagnetic      -E.M. spectrum
spectrum              chart analysis
-Group work:
making a quipu

-visible light        summary tables,     light
-UV radiation         poster contest     -discharge tubes
-X-rays                                  -gamma detectors
-gamma rays

4. Final review           -Science conference
-E.M. spectrum trial
-Test
```

### Unit Description

#### (1) Electromagnetic Waves

The first couple of days should be devoted to discussing the general properties of electromagnetic waves. The direction of such class discussions and the complexity of material will depend on how well the students are prepared for the material. Pre-test that includes general questions can help a teacher identify the level of student preparedness. At this stage, the goal is to show the students the differences and similarities between waves existing only in a medium and electromagnetic waves. The following summary charts and diagrams can be helpful.

#### (2) Electromagnetic Spectrum

The second stage is to combine all electromagnetic waves in one spectrum. The main goal is to show the students different options for such a spectrum: vertical or horizontal, according to the wavelength or frequency of radiation. It is very important to demonstrate different types of electromagnetic spectrum charts taken from different sources (textbooks, encyclopedia, etc.). In addition, the teacher can give students assignments to develop their own spectrum structures based on other principles.

A very interesting and non-traditional way to identify each type of radiation in a spectrum is to create a "quipu" that contains complete information about this spectrum. Quipu, a so-called knotted-rope-artifact, is a mysterious way of coding and decoding any type of data in a very compact and unusual manner. This method was used by the ancient Incas. Using knots of different shapes (single, figure eight, and long knots) and strings of various lengths and thicknesses, students not only can arrange electromagnetic waves in a spectrum, but also insert any other type of information (wavelength, frequency, energy, etc.).

After quipus are constructed, groups can exchange them and try to decipher the coded information by analyzing how the strings are grouped together, how many strings there are in each group, and according to what pattern the knots are arranged. Here is an example of an electromagnetic spectrum quipu based on frequency. First string represents the speed of light. It is considered to be a key string that gives the idea of how to insert numbers with scientific notations using different types of knots. Other six strings represent six types of electromagnetic waves ( from radio waves to gamma rays.)

#### (3) Types of Radiation: sources and properties

The next, and perhaps, central part of this unit is a detailed description of each type of radiation. To increase the efficiency and to avoid repetition, it is logical to organize the whole process in the form of independent work in small groups. The whole class is divided into six groups, which are assigned to investigate a type of radiation in accordance with a certain format.

Students are responsible for organizing library research (using school and public libraries), conducting experiments (under the teacher's supervision), filling out a special summary table (the table should be big enough to be posted in class), and making group presentations of their investigations in front of the class.

The final presentation and summary table should include the following information: Type of radiation, astronomical sources, artificial sources, properties, methods of detection, discovery, and wavelength/frequency.

In addition to (or instead of) the class presentation, there are other interesting activities that may be organized in this part of the unit. In order to emphasize astronomical issues related to electromagnetic radiation, it would be helpful, for example, to have a poster contest. The poster themes could be:
• how to "see" invisible radiation,
• extreme ultraviolet sources in the Universe,
• use of radio waves for communication between civilizations,
• Universe as seen in different types of radiation,
• advanced astrophysics technology of the 21st century,
• the infrared world, etc.

#### (4) Recapitulation and Review

There are different ways to review the material studied in the unit and to prepare students for the test. Class discussions, review worksheets, or a movie about electromagnetic waves are among possible activities. Another interesting form of a review lesson could be a science conference entitled "Electromagnetic radiation in astrophysics." Students can use charts, tables, slides, OHPs, and even VCRs to support their ideas while making presentations. The following are some of the possible topics for discussion:

• evolution of a star, and radiation,
• history of NASA missions,
• size of the Universe, and the Hubble Space Telescope,
• extreme ultraviolet radiation and white dwarfs,
• the search for other planetary systems,
• advanced X-ray astrophysics and supernova stars,
• astrophysics data system,
• EUVE satellite mission and new discoveries in astronomy, etc.

But the most non-traditional way to summarize and review the material studied in this unit is to put the electromagnetic spectrum "On Trial" in an unusual but educational lesson-game.
For further information on these topics:

"Astrophysics": Elective Subject for High School Students