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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.

λ=cf
f=cλ
f=3×108400×10-9
f=7,5×1014  Hz

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.

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

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.