Episode 314: Electromagnetic radiation
Lesson for 16-19
- Activity time 70 minutes
- Level Advanced
This episode extends students’ understanding of the nature of different types of electromagnetic radiation, and considers their shared nature.
- Demonstration: Beyond the visible spectrum (10 minutes)
- Student presentation: Regions of the electromagnetic spectrum (30 minutes)
- Student questions: General aspects of the spectrum (30 minutes)
Demonstration: Beyond the visible spectrum
Set up a spectrum of visible light. To do this, shine a bright white light source through either a prism or a diffraction grating.
(Note that a prism is often used, but that a diffraction grating is much simpler and more reliable. At this stage, it is harder for students to understand how a diffraction grating works, but you can promise that they will soon know!)
Display the spectrum on a white screen.
Use a phototransistor or other infra-red detector to show that the spectrum extends beyond the red. Use fluorescent paper to show that it extends beyond the violet. (Alternatively, use a fluorescent marker pen, of the type used for security labelling.
(Be sure to check that these methods work before showing this to a class.)
It can help students to understand the continuous nature of the spectrum if you relate colours to temperatures. Any object emits infrared; heat it to 500 ° C and it glows dull red; heat it to 1 000 ° C and it glows white hot.
Student presentation: Regions of the electromagnetic spectrum
In advance of this episode, ask students to find out about a particular region of the electromagnetic spectrum. They should find out about:
- wavelengths, frequencies and speeds
- methods of production
- methods of detection
Note that the regions of the spectrum are not well-defined. You could include terahertz radiation, a part of the spectrum which is rapidly gaining importance.
An alternative approach would be to ask individuals to research the importance of different types of electromagnetic radiation in different spheres of interest – medicine, astronomy, communications, the historical development of physics, etc.
Ask students to present their findings in turn; provide a suitable blank table for them to record a summary.
This can be used as an OHT to show how the radio wave and microwave regions can be subdivided.
Student questions: General aspects of the spectrum
These questions will help to focus students’ attention on the general features of the spectrum.