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Electromagnetic Spectrum

11.3 Electromagnetic spectrum (ESADK)

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 11.1 lists the wavelength and frequency ranges of the divisions of the electromagnetic spectrum.

Category

Range of Wavelengths (nm)

Range of Frequencies (Hz)

gamma rays

\(< 1\)

\(> \text{3} \times \text{10}^{\text{17}}\)

X-rays

\(1–10\)

\(\text{3} \times \text{10}^{\text{16}} – \text{3} \times \text{10}^{\text{17}}\)

ultraviolet light

\(10–400\)

\(\text{7,5} \times \text{10}^{\text{14}} – \text{3} \times \text{10}^{\text{16}}\)

visible light

\(400–700\)

\(\text{4,3} \times \text{10}^{\text{14}} – \text{7,5} \times \text{10}^{\text{14}}\)

infrared

\(700 – \text{10}^{\text{5}}\)

\(\text{3} \times \text{10}^{\text{12}} – \text{4,3} \times \text{10}^{\text{14}}\)

microwave

\(\text{10}^{\text{5}} – \text{10}^{\text{8}}\)

\(\text{3} \times \text{10}^{\text{9}} – \text{3} \times \text{10}^{\text{12}}\)

radio waves

\(> \text{10}^{\text{8}}\)

\(< \text{3} \times \text{10}^{\text{9}}\)

Table 11.1: Electromagnetic spectrum

Examples of some uses of electromagnetic waves are shown in Table 11.2.

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

Table 11.2: Uses of EM waves

EM radiation

Exercise 11.1

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

Solution not yet available

Calculate the frequency of an EM wave with a wavelength of \(\text{400}\) \(\text{nm}\).

Solution not yet available

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.

Solution not yet available

Figure 11.2: 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).

The EM spectrum is continuous (has no gaps) and infinite. Due to technological limitations, we can only use electromagnetic radiation with wavelengths between \(\text{10}^{-\text{14}}\) \(\text{m}\) and \(\text{10}^{\text{15}}\) \(\text{m}\).