Electromagnetic Waves  
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Are a self – propagating transverse wave of oscillating electric and magnetic fields  
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OR: Are the waves which are propagated through space or matter by the  
vibration of an electric field and magnetic field at right angles to one another  
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Self-propagating means a change in electric field produces a change in  
magnetic field and vice versa  
Examples are Radio waves, Microwaves, Infrared radiation, Visible light ,  
Ultraviolet rays, X–rays, Gamma rays  
NB:  
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It is produced when electrically charged particles oscillate or change energy  
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The greater the energy change, the higher the frequency of the resulting wave  
Electric field and magnetic field of an electromagnetic wave are perpendicular to each other  
Properties of Electromagnetic Waves  
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They do not require material medium to travel through  
They undergoes reflection, refraction, interference and diffraction  
They travel at the speed of light (i.e C = 3 x108 m/s in vacuum  
)
They carry no electric charge  
They transfer energy in form of oscillating electric and magnetic fields  
They obey the wave equation, C =  
풇λ  
Electromagnetic Spectrum  
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Is a continuous band of all electromagnetic waves arranged in order of  
increasing or decreasing frequencies or wavelength change.  
It is divided into seven regions or bands  
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Tables of Electromagnetic Spectrum  
Wavelength (m)  
Region (band)  
Radio waves  
Micro waves  
Infrared  
Visible light  
Ultraviolet light  
X-rays  
Frequency (Hz)  
>10-1  
>3 x 109  
10-1 – 10-4  
3x109 - 3x1012  
3x1012 - 4.3x1014  
4.3x1014 - 7.5x1014  
7.5x1014 - 3x1017  
3x1017 - 3x1019  
>3x1019  
10-4 – 10-7  
7x10-7 – 4 x 10-7  
4x10-7 – 10-9  
10
-9
–
10
-11  
<10
-11  
Gamma rays  
Electromagnetic Spectrum Observation  
✓
It is continuous: means each band merges into next and there is no gap  
between their frequencies  
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Some Wave length overlap: in some cases there is an overlap of wave length  
so we have to name according to source not to the wave length, for Example,  
X-rays and Gamma rays  
Sources, Detectors, and uses of EMW  
Radiation  
Detector  
Uses  
Source  
Gamma rays  
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Radioactive  
substance  
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Photographic  
plate  
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in medicine to locate  
internal body organs  
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Geiger muller tube  
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sterilize surgical  
equipment  
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To detect flaws in metals  
X
–rays  
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x –rays tubes  
Detect fractured bones  
and dislocations  
Treatment of cancer  
Study of crystal structure  
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fluorescent  
screens  
photographic film  
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Ultra violet  
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the sun  
sparks  
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photographic films  
photocells  
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Detect forgeries e.g  
bank notes  
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mercury vapor  
lamp  
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paper smeared  
with vaseline  
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Source of vitamin D  
To kill bacteria in water  
Visible light  
Infra red  
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The sun  
Luminous  
objects  
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The eye  
Photocells  
Photographic films  
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Ordinary photography  
Enables the eye to see  
Photosynthesis  
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The sun  
Fires  
Hot bodies  
Infrared photography  
Drying substances  
locate overheating in  
electric system  
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Thermometer with  
blackened bulbs  
Thermopile  
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Bolometer  
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Used in remote control,  
night vision device, fibre-  
optic telecommunication  
and security system  
Are used for welding  
plastics, drying prints, etc  
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Microwaves  
Radio waves  
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Magnetrons in  
microwave  
oven  
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Solid state diodes  
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For cooking in  
microwaves ovens  
Satellite communication  
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Radar communication  
Used for broadcasting of  
information by radio and  
television channels  
Used by astronomers to  
collect and study radio  
waves from distant stars  
and galaxies.  
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Oscillating  
electric circuits  
Objects in space  
e.g planets,stars  
etc  
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Aerials  
Diodes  
Earphones in  
electric circuits  
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N.B: RADAR = Radio  
Detection  
A
nd  
Ranging  
Example  
1. What is the wavelength of radio waves of frequency 95.6MHz?(c = 3.0 x 108 m/s)  
Soln:  
( )  
From: 풗 풄 = 풇흀  
ퟖ
풗
ퟑ 풙 ퟏퟎ  
∴ 흀 = =  
= ퟑ. ퟏퟒ 풎  
ퟔ
풇
ퟗퟓ.ퟔ 풙ퟏퟎ  
Class Assignment  
1. (a) Explain why radio waves are similar to light waves but not sound waves  
(b) A radio station transmits a signal of wave 1500m. Calculate the frequency of  
this signal (ANS: ƒ = 200 KHz)  
2. Light of frequency 4.6 × 1014Hz travels at a speed of 1.24 × 108ms-1 in diamond.  
Calculate the refractive index of diamond for this color of light. (ANS:  
흁
= 2.42  
)
3. (a) What is diffraction of wave?  
(b) Illustrate how plane water wave fronts are diffracted on passing through a narrow gap