The Electromagnetic Spectrum
The electromagnetic spectrum is one continuous range of wavelengths. Know the order, the rough sizes, that shorter wavelength means higher frequency and higher energy, and which everyday device uses which kind of radiation.
Key Facts to Memorize
Order of the spectrum
Radio → Microwave → Infrared → Visible → Ultraviolet → X-ray → Gamma Wavelength gets shorter; frequency and energy get higher. In visible light, violet is shortest and red is longest.
Key equations
c = λν with c = 3.00 × 10⁸ m/s E = hν with h = 6.626 × 10⁻³⁴ J·s
Radio
FM/AM broadcasts, Wi-Fi, cell signals, MRI machines.
Microwave
Microwave ovens, radar, satellite communications.
Infrared
TV remotes, night-vision goggles, thermal cameras, heat lamps.
Visible
Sunlight, lamps, laser pointers, anything your eyes can detect.
Ultraviolet
Sunburn, black lights, sterilizing lamps, tanning beds.
X-ray
Medical and dental imaging, airport security scanners.
Gamma
Nuclear decay, cancer radiation therapy, cosmic sources.
Radio: Wavelength & Frequency
Wavelength: longer than 1 m (up to km) Frequency: below about 3 × 10⁸ Hz (lowest)
Microwave: Wavelength & Frequency
Wavelength: about 1 mm to 1 m Frequency: about 3 × 10⁸ to 3 × 10¹¹ Hz
Infrared: Wavelength & Frequency
Wavelength: about 700 nm to 1 mm Frequency: about 3 × 10¹¹ to 4 × 10¹⁴ Hz
Visible: Wavelength & Frequency
Wavelength: about 400–700 nm (violet to red) Frequency: about 4 × 10¹⁴ to 7.5 × 10¹⁴ Hz
Ultraviolet: Wavelength & Frequency
Wavelength: about 10–400 nm Frequency: about 7.5 × 10¹⁴ to 3 × 10¹⁶ Hz
X-ray: Wavelength & Frequency
Wavelength: about 0.01–10 nm Frequency: about 3 × 10¹⁶ to 3 × 10¹⁹ Hz
Gamma: Wavelength & Frequency
Wavelength: shorter than 0.01 nm (smallest) Frequency: above 3 × 10¹⁹ Hz (highest)
Radio: Matter Interaction
Causes nuclear spin flips (used in MRI) and makes electrons in antennas oscillate.
Microwave: Matter Interaction
Causes molecules (like water) to rotate, producing heat.
Infrared: Matter Interaction
Causes bonds in molecules to vibrate (stretch and bend) — felt as heat.
Visible: Matter Interaction
Excites valence (outer) electrons to higher energy levels — gives color.
Ultraviolet: Matter Interaction
Excites or removes electrons and can break chemical bonds (damages DNA).
X-ray: Matter Interaction
Ionizes atoms by knocking out inner-shell (core) electrons.
Gamma: Matter Interaction
Highly ionizing; can break apart molecules and interact with atomic nuclei.
Al says…
Remember the order with 'Raging Martians Invaded Venus Using X-ray Guns': Radio, Microwave, Infrared, Visible, Ultraviolet, X-ray, Gamma. Then walk through your house: radio in the car, microwave in the kitchen, infrared in the TV remote, visible from the lamp, UV out the window.
Practice This Topic
External Tools
- Blooket review game
Coming soon — Mrs. Cauthron will post the game link here.
- NASA: Introduction to the EM spectrum
Short, readable pages for each region.
- NASA EM spectrum tour
Photos of each region in real use.