Electromagnetic spectrum

Electromagnetic (EM) waves are a family of waves that include radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma (γ) rays. All EM waves are produced by oscillating electric and magnetic fields.

A clean, minimalist diagram showing a transverse electromagnetic wave. Show perpendicular electric and magnetic field vectors oscillating at right angles to the direction of wave travel. Use simple lines and arrows, with clear labels: 'Electric field', 'Magnetic field', and 'Direction of travel'.

All electromagnetic waves are transverse waves, meaning the oscillations are perpendicular to the direction of energy transfer. In a vacuum (free space), all EM waves travel at the same speed, known as the speed of light, cc.

Definition

The electromagnetic spectrum is the continuous range of electromagnetic waves arranged in order of increasing frequency (or decreasing wavelength).

Speed of Electromagnetic Waves

All electromagnetic waves travel at the same speed in free space:

Formula
c=3.0×108 m s−1c = 3.0 \times 10^8 \ \text{m s}^{-1}

Regions of the Electromagnetic Spectrum

The electromagnetic spectrum is divided into principal regions according to wavelength (or frequency). The main regions, from longest to shortest wavelength, are:

A horizontal, minimalist bar or spectrum showing the electromagnetic spectrum from radio waves (left, longest wavelength) to gamma rays (right, shortest wavelength). Each region (radio, microwave, infrared, visible, ultraviolet, X-ray, gamma) is clearly labeled. Indicate the visible light region with a subtle color gradient. Keep the design clean and modern.

RegionApproximate Wavelength Range (in free space)
Radio waves>1> 1 m
Microwaves10−310^{-3} m to 11 m
Infrared7×10−77 \times 10^{-7} m to 10−310^{-3} m
Visible light4×10−74 \times 10^{-7} m to 7×10−77 \times 10^{-7} m
Ultraviolet10−810^{-8} m to 4×10−74 \times 10^{-7} m
X-rays10−1310^{-13} m to 10−810^{-8} m
Gamma rays<10−13< 10^{-13} m
Important

Always include units with every physical quantity.

Visible Light

The only part of the electromagnetic spectrum visible to the human eye is called visible light. Its wavelength range in free space is approximately 400–700 nm (1 nm=1×10−91 \ \text{nm} = 1 \times 10^{-9} m).

  • Violet: ≈400\approx 400 nm
  • Red: ≈700\approx 700 nm

A minimalist, horizontal gradient bar representing the visible spectrum from violet (left, 400 nm) to red (right, 700 nm). Label the ends with 'Violet (400 nm)' and 'Red (700 nm)'. Keep the design clean and modern.

Summary

  • All EM waves are transverse and travel at c=3.0×108c = 3.0 \times 10^8 m s−1^{-1} in free space.
  • The EM spectrum includes radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays, ordered by decreasing wavelength.
  • Only wavelengths between 400–700 nm are visible to the human eye.
Exam Tip

You may be asked to recall the order of regions in the electromagnetic spectrum or estimate their wavelength ranges. Remember the order from longest to shortest wavelength: radio, microwave, infrared, visible, ultraviolet, X-ray, gamma.

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