Everything Science Grade 12

CHAPTER 15. EM RADIATION 15.4

c = fλ

3 × 108 = f× 200 × 10 −^9

f = 1. 5 × 1015 Hz

Examples of some usesof electromagnetic waves are shown in Table 15.2.

Table 15.2: Uses of EMwaves

Category Uses

gamma rays used to kill the bacteriain marshmal-

lows and to sterilise medical equip-

ment

X-rays used to image bone structures

ultraviolet light bees can see into the ultraviolet be-

cause flowers stand outmore 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

In theory the spectrumis infinite, although realistically we can only observe wave-
lengths from a few hundred kilometres to those of gamma rays due toexperimental
limitations.

Humans experience electromagnetic waves differently depending on their wavelength.
Our eyes are sensitive tovisible light while our skin is sensitive to infrared, and many
wavelengths we do notdetect at all.

Exercise 15 - 3

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


2. Calculate the frequency of an EM wave with awavelength of 400 nm.


3. Give an example ofthe use of each type ofEM radiation: gamma rays, X-rays,
   ultraviolet light, visible light, infrared, microwave and radio and TV waves.

More practice video solutions or help at http://www.everythingscience.co.za

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