Electromagnetic spectrum

EM radiation is classified into types according to the frequency of the wave: these types include, in order of increasing frequency, radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays and gamma rays.

Table 1 lists the wavelength and frequency ranges of the divisions of the electromagnetic spectrum.

Table 1: Electromagnetic spectrum

Category	Range of Wavelengths (nm)	Range of Frequencies (Hz)
gamma rays	< 1	> 3 × 10¹⁹
X-rays	1–10	3 × 10¹⁷ – 3 × 10¹⁹
ultraviolet light	10–400	7,5 × 10¹⁴ – 3 × 10¹⁷
visible light	400–700	4,3 × 10¹⁴ – 7,5 × 10¹⁴
infrared	700 – 10⁵	3 × 10¹² – 4,3 × 10¹⁹
microwave	10⁵ – 10⁸	3 × 10⁹ – 3 × 10¹²
radio waves	> 10⁸	< 3 × 10⁹

Examples of some uses of electromagnetic waves are shown in Table 2.

Table 2: Uses of EM waves

Category	Uses
gamma rays	used to kill the bacteria in marshmallows and to sterilise medical equipment
X-rays	used to image bone structures
ultraviolet light	bees can see into the ultraviolet because flowers stand out more clearly at this frequency
visible light	used by humans to observe the world
infrared	night vision, heat sensors, laser metal cutting
microwave	microwave ovens, radar
radio waves	radio, television broadcasts

Exercise 1: EM radiation

Problem 1:

Arrange the following types of EM radiation in order of increasing frequency: infrared, X-rays, ultraviolet, visible, gamma.

Answer 1:

Infrared, visible, ultra-violet, X-rays, gamma

Problem 2:

Calculate the frequency of an EM wave with a wavelength of 400 nm.

Answer 2:

λ = \frac{c}{f}

f = \frac{c}{λ}

f = \frac{3 \times 10^{8}}{400 \times 10^{- 9}}

f = 7, 5 \times 10^{14} Hz

Problem 3:

Give an example of the use of each type of EM radiation, i.e. gamma rays, X-rays, ultraviolet light, visible light, infrared, microwave and radio and TV waves.

Answer 3:

Gamma rays: Studying the physics of stars by observing gamma ray bursts in space

X-rays: Searching baggage at the airport

ultra-violet: Used in sun beds to help people get a tan during winter. NB! Dangerous!

Visible light: Used in Light Emitting Diodes for use as indicator lights in electronic equipment

infrared: Used for night-vision goggles, objects emit infrared radiation because they are warm and can therefore be detected at night using infrared goggles.

Microwaves: Microwave ovens emit microwave radiation that excites motion in water molecules in foodstuffs, thereby warming it up

radio waves: Use for telecommunication

TV waves: see radio waves.

**Figure 1:** The electromagnetic spectrum as a function of frequency. The different types according to wavelength are shown as well as everyday comparisons.

EM radiation in the visible part of the spectrum is scattered off all of the objects around us. This EM radiation provides the information to our eyes that allows us to see. The frequencies of radiation the human eye is sensitive to constitute only a very small part of all possible frequencies of EM radiation. The full set of EM radiation is called the electromagnetic spectrum. To simplify things the EM spectrum divided into sections (such as radio, microwave, infrared, visible, ultraviolet, X-rays and gamma-rays).

Radio waves, microwaves and infrared radiation

The EM spectrum is continuous (has no gaps) and infinite. Due to technological limitations, we can only use electromagnetic radiation with wavelengths between 10⁻¹⁴ m and 10¹⁵ m.

« Previous: Wave-like nature of EM radiation Next: Penetrating ability of EM radiation »

Everything

Science

Electromagnetic spectrum

Exercise 1: EM radiation