1. Electromagnetic Spectrum
Understanding the relation between color, temperature and energy.
AUTHORS:
Jasmeet K Dhaliwal, Scripps Institution of Oceanography, UCSD
Jason Moore, San Diego High School: School of the Arts
SUMMARY: This specific lesson can be used in a unit prior to chemistry to introduce the electromagnetic spectrum, or as a review later in the year. This presentation includes a simple activity using “mood beads,” which may be more appropriate for classes such as freshman Earth Science (vs. upper-classmen Chemistry).
CONTEXT FOR USE: This is an introduction to the chemistry unit, which draws on stellar nucleosynthesis as a context for explaining how atoms are built.
MISCONCEPTIONS:
Warm colors are red, orange and yellow and are therefore hotter
Cool colors are green, violet and blue and therefore have lower energy

2. Mood Beads
The ‘mood’ beads contain a liquid crystal
It is a thermochromatic crystal.
This means that it changes color when exposed to heat.
MAIN POINT: An ice-breaker to introduce the idea of color as a measure of energy (or temperature)
TEACHING NOTES:
The students are given mood beads to experiment with and observe. The objective of this activity is to prompt them to think about the reasons why the mood beads change color. They are in fact liquid crystals that respond to changes in thermal energy (heat). In order to allow the students to brainstorm, they should be allowed to discuss the following questions with a partner or in small groups.
What do the mood beads do when they are touched?
Why do they change color? (Are they actually indicating your ‘mood’?)
a)) How is it obtaining its information?
b) What does it represent? (body heat)
3) What can color tell you about energy?
4) How do the colors differ in energy? (i.e. reds, oranges vs. blues and violets) How about white?
This should then be brought into a full classroom discussion, with the objective of discussing the relation between color and temperature (or energy).
REFERENCES:
Thermochromism
Mood rings and mood beads use liquid crystals that exhibit thermochromism, which refers to the property of a substance to change color as a result of a change in temperature. In liquid crystals, this change in color is because of different reflection of certain wavelengths through the structure of the material (which transforms at different temperatures).
The mood beads can be purchased online. Alternatively, a class set of mood rings would also suffice. A quick search in Amazon will prove useful, such as:
PICTURE/GRAPHICS CREDITS:
Mood Beads: These are made of a thermochromatic liquid crystal and so will change when exposed to heat.

3. Electromagnetic Radiation
A type of radiation that includes both varying electric and magnetic fields.
This includes visible light, UV rays and infrared.
MAIN POINT: Electromagnetic Radiation occurs in different forms, but is present everywhere.
TEACHING NOTES:
Electromagnetic radiation is an important phenomenon in which waves with both electric and magnetic properties carry radiant energy through space. They are different types of electromagnetic radiation and are categorized by their frequency or wavelength (these properties are inversely related: frequency increases as wavelength decreases). In order of increasing frequency, electromagnetic radiation consists of the following: radio waves, microwaves, infrared radiation, visible light, ultraviolet (UV) radiation, X-rays, and gamma rays. This is detailed further in the next slide on the electromagnetic spectrum.
As the image shows above, different information is communicated by the various types to electromagnetic radiation. The image on the left only shows the Orion constellation in visible light, while the image on the right has the added information of “thermal emission,” which is represented by infrared radiation. In this way, it is evident that in order to understand different characteristics of an object (i.e. such as the color and thermal energy of a star), it is important to observe and measure it using different types of electromagnetic radiation.
It is also important to note that sound waves are not part of electromagnetic radiation; they are pressure waves that involve the compression of molecules.
REFERENCES:
Electromagnetic Radiation:
Measuring Infrared Radiation:
PICTURE/GRAPHICS CREDITS:
Orion Constellation
This image is an example of different types of electromagnetic radiation. Both images are of the Orion constellation, but the left shows visible light, while the right shows infrared radiation (in false color). 3

4. Electromagnetic Spectrum
The range of all possible frequencies of electromagnetic radiation.
Radio waves have the lowest frequency and therefore the lowest energy.
In contrast, gamma rays have the highest frequency and energy, but the shortest wavelength.
MAIN POINT: The electromagnetic spectrum represents the range of all possible types of electromagnetic radiation.
TEACHING NOTES:
The electromagnetic spectrum displays the types of radiation from the lowest frequencies (on the left) to the highest frequencies (on the right). This also corresponds to the longest wavelengths (on the left) and the shortest wavelengths (on the right). This demonstrates the inverse relationship between frequency and wavelength: as one decreases, the other increases.
The spectrum is ordered as follows: radio waves, microwaves, infrared radiation, visible light, UV light, X-ray light, gamma rays. Because of their shorter wavelength (and therefore higher frequency and energy), UV light, X-rays and gamma rays are able to penetrate materials more easily; this is also why these types of radiation are dangerous to human health.
Without special instruments, humans can only observe visible light, which ranges between 380 nm and 760 nm (nm = nanometers; measure of wavelength). The other types of radiation need to be observed with instruments that are sensitive to different types of electromagnetic radiation.
REFERENCES:
Electromagnetic Spectrum:
PICTURE/GRAPHICS CREDITS:

5. Hertzsprung Russell Diagram
The Hertzsprung Russel diagram shows the relation between temperature and luminosity in stars
The Main Sequence of Stars runs through the middle of the diagram
(bottom right to top left)
The Sun is an example of a Main Sequence star.
MAIN POINT: The Hertzsprung Russell (HR) diagram illustrates the relation between temperature and luminosity in stars.
TEACHING NOTES:
The H-R diagram is a scatter plot that shows the relationship between a star’s luminosity / brightness (also known as ‘absolute magnitude’) versus its spectral type and associated temperatures (where there is a general relation between luminosity and temperature). The main aspect of the diagram is the diagonal that stretches across; this represents the ‘main sequence’ of stars where the upper-left ones are hot and bright and the lower-right ones are cooler and less bright. There are also non-main sequence stars represented on the diagram; the white dwarfs are along the lower left while giants and supergiants are found in the top right. This diagram is explained in greater detail in the next lesson.
REFERENCES:
H-R Diagram:
PICTURE/GRAPHICS CREDITS: 5

6. Summary
The mood beads are an ice-breaker activity to introduce the students to the electromagnetic spectrum.
The electromagnetic spectrum describes different forms of radiation, from radio waves to gamma rays.
The Hertzsprung Russell diagram describes the relation between temperature and luminosity in stars.
The Main Sequence stars are represented by the main branch on this diagram.
The Sun is an example of a Main Sequence star. 6