S4.10.7 For the adult
The electromagnetic spectrum
In empty space, a radio wave and a gamma ray leave a star at the same moment. Which reaches the Earth first?
What this chapter teaches
Electromagnetic waves are transverse waves that need no medium and all travel at 3 × 10⁸ m/s in a vacuum. In order of falling wavelength and rising frequency: radio, microwave, infrared, visible, ultraviolet, X-ray, gamma. Each has uses. c = fλ links frequency and wavelength.
Three questions to ask
There is no one right wording. Listen for the idea.
- Can you list the electromagnetic waves, from longest wavelength to shortest?
- Why do a radio wave and a gamma ray from the same star arrive together?
- A wave has a frequency of 100 MHz. How would you find its wavelength?
After the chapter, the learner can
- List electromagnetic waves in order of wavelength and frequency
- Give a use of each kind of electromagnetic wave
What they copy into their notebook
Radio, microwave, infrared, visible, ultraviolet, X-ray, gamma: wavelength falls, frequency rises. All go at 3 × 10⁸ m/s in a vacuum. c = fλ.