Electromagnetic Spectrum Examples in Physics

Start with the recap, study the fully worked examples, then use the practice problems to check your understanding of Electromagnetic Spectrum.

This page combines explanation, solved examples, and follow-up practice so you can move from recognition to confident problem-solving in Physics.

Concept Recap

The complete continuum of all electromagnetic waves, organized in order of increasing frequency (or decreasing wavelength).

A 'rainbow' that extends far beyond visible light in both directions.

Read the full concept explanation →

How to Use These Examples

  • Read the first worked example with the solution open so the structure is clear.
  • Try the practice problems before revealing each solution.
  • Use the related concepts and background knowledge badges if you feel stuck.

What to Focus On

Core idea: Same type of wave, just different frequencies = different properties and uses.

Common stuck point: Visible light is only a tiny sliver of the full EM spectrum; most EM radiation is invisible to the human eye.

Sense of Study hint: When answering EM spectrum questions, recall the order from low to high frequency: Radio, Microwave, Infrared, Visible, Ultraviolet, X-ray, Gamma ray. Then identify the properties asked about — longer wavelength means lower frequency and lower photon energy. Finally, match each region to its common applications.

Worked Examples

Example 1

easy
Arrange the following EM waves from lowest to highest frequency: visible light, X-rays, radio waves, ultraviolet, infrared, gamma rays, microwaves.

Solution

  1. 1
    The electromagnetic spectrum from lowest to highest frequency: radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, gamma rays.
  2. 2
    This is also the order from longest to shortest wavelength.
  3. 3
    All travel at the same speed (c = 3 \times 10^8 \text{ m/s}) in a vacuum.

Answer

\text{Radio} < \text{Microwave} < \text{IR} < \text{Visible} < \text{UV} < \text{X-ray} < \text{Gamma}
The electromagnetic spectrum encompasses all EM waves ordered by frequency (or wavelength). Higher frequency means shorter wavelength and more energy per photon. All EM waves travel at the speed of light.

Example 2

medium
A photon of ultraviolet light has a wavelength of 200 \text{ nm}. What is its energy? Use c = 3 \times 10^8 \text{ m/s} and h = 6.626 \times 10^{-34} \text{ J s}.

Practice Problems

Try these problems on your own first, then open the solution to compare your method.

Example 1

medium
A cell phone operates at 800 \text{ MHz} and an X-ray machine at 3 \times 10^{18} \text{ Hz}. By what factor is the X-ray frequency greater than the cell phone frequency?

Example 2

hard
The human eye detects light from 380 \text{ nm} (violet) to 700 \text{ nm} (red). What is the range of frequencies for visible light? What fraction of the full EM spectrum (from 3 \text{ Hz} radio to 3 \times 10^{20} \text{ Hz} gamma) does visible light occupy? Use c = 3 \times 10^8 \text{ m/s}.
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Background Knowledge

These ideas may be useful before you work through the harder examples.

electromagnetic wavesfrequencywavelength