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# 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.

Electromagnetic spectrum

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

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

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

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

 $\lambda =\frac{c}{f}$ $f=\frac{c}{\lambda }$ $f=\frac{3×{10}^{8}}{400×{10}^{-9}}$

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.

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.

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.