recall the approximate range of wavelengths in free space of the principal regions of the electromagnetic spectrum from radio waves to γ-rays

Published by Patrick Mutisya · 14 days ago

Electromagnetic Spectrum – Cambridge A‑Level Physics 9702

Electromagnetic Spectrum

Learning Objective

Recall the approximate range of wavelengths in free space for the principal regions of the electromagnetic spectrum, from radio waves to γ‑rays.

Wavelength and Frequency Ranges

The electromagnetic spectrum is continuous, but for practical study we divide it into regions. The table below lists the typical wavelength (\$\lambda\$) and corresponding frequency (\$\nu\$) ranges for each region in free space.

RegionWavelength, \$\lambda\$ (meters)Frequency, \$\nu\$ (hertz)
Radio waves\$10^{3}\,\text{m}\$ to \$10^{-1}\,\text{m}\$\$3\times10^{5}\,\text{Hz}\$ to \$3\times10^{9}\,\text{Hz}\$
Microwaves\$10^{-1}\,\text{m}\$ to \$10^{-3}\,\text{m}\$\$3\times10^{9}\,\text{Hz}\$ to \$3\times10^{11}\,\text{Hz}\$
Infrared (IR)\$10^{-3}\,\text{m}\$ to \$7\times10^{-7}\,\text{m}\$\$3\times10^{11}\,\text{Hz}\$ to \$4.3\times10^{14}\,\text{Hz}\$
Visible light\$7\times10^{-7}\,\text{m}\$ to \$4\times10^{-7}\,\text{m}\$\$4.3\times10^{14}\,\text{Hz}\$ to \$7.5\times10^{14}\,\text{Hz}\$
Ultraviolet (UV)\$4\times10^{-7}\,\text{m}\$ to \$10^{-9}\,\text{m}\$\$7.5\times10^{14}\,\text{Hz}\$ to \$3\times10^{17}\,\text{Hz}\$
X‑rays\$10^{-9}\,\text{m}\$ to \$10^{-11}\,\text{m}\$\$3\times10^{17}\,\text{Hz}\$ to \$3\times10^{19}\,\text{Hz}\$
γ‑rays\$<10^{-11}\,\text{m}\$\$>3\times10^{19}\,\text{Hz}\$

Key Points to Remember

  • The wavelength and frequency are related by \$c = \lambda \nu\$, where \$c \approx 3.00\times10^{8}\,\text{m·s}^{-1}\$ is the speed of light in vacuum.

  • Each region overlaps slightly with its neighbours; the limits given are conventional approximations.

  • Moving from radio waves to γ‑rays, the wavelength decreases by more than 20 orders of magnitude while the frequency increases by the same factor.

  • Different regions are useful for different applications (e.g., radio for communication, infrared for thermal imaging, visible for human vision, U \cdot for sterilisation, X‑rays for medical imaging, γ‑rays for nuclear physics).

Suggested Diagram

Suggested diagram: A logarithmic scale showing the electromagnetic spectrum from radio waves (long wavelength, low frequency) to γ‑rays (short wavelength, high frequency), with the approximate boundaries indicated.