The seven groups in order, what they share, c = fλ in standard form, and timing radar echoes and satellite signals.
What you will learn
- Put the seven groups in order of frequency or wavelength
- Use v = fλ with 3.00 × 10⁸ m/s and standard form
- Find a distance from a signal's travel time
One family, seven groups
Electromagnetic (EM) waves are transverse waves that transfer energy from a source to an absorber.
Light is one of them; it just happens to be the band our eyes detect.
In order of increasing frequency (and so decreasing wavelength):
- Radio waves (wavelengths from about a millimetre to kilometres)
- Microwaves (around a centimetre)
- Infrared (around 0.01 mm)
- Visible light (400 nm violet to 700 nm red)
- Ultraviolet (around 50 nm)
- X-rays (around 0.1 nm)
- Gamma rays (smaller than an atom)
The spectrum is continuous: the groups merge into each other. Make up your own memory sentence from the first letters R, M, I, V, U, X, G; one you invent sticks better than one you are given.
Every EM wave travels at the same speed in a vacuum, 3.00 × 10⁸ m/s, and almost as fast in air. Papers give you this value.
The rest of this lesson and its 11 practice questions are locked.
In this lesson
- One family, seven groups
- v = fλ for EM waves
- Timing signals
- Try it: Frequency from a wavelength
11 practice questions, marked as you go; about 25 minutes in all.
Key terms
Increasing frequency, Decreasing wavelength
In this unit: Waves and the electromagnetic spectrum
Transverse and longitudinal waves, v = fλ and the wave practicals, reflection and refraction, and the electromagnetic spectrum with its uses, dangers and the infrared practical.