nature of em wave
DESCRIPTION
plus two physicsTRANSCRIPT
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• Electromagnetic radiation is a disturbance in an electric field.
• This results in a magnetic field at right angles to the electric one.
• Therefore it is called an electromagnetic radiation – electric and magnetic disturbances result!
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It propagates (moves) through space carrying energy from one place to
another
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• All electromagnetic waves (also called electromagnetic photons) can travel through a vacuum – it is the only way that energy can propagate through space
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• Wavelength is the smallest distance between two corresponding points on a wave.
• It is given the symbol and is measured in metres.
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The wave equation
wave speed (metre/second, m/s) = frequency (hertz, Hz) × wavelength (metre, m)
wavespeed = f
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• All electromagnetic radiation travels through a vacuum at the same speed – the speed of light – symbol ‘c’ – which is 300,000,000 m/s
• This is the fastest speed anything can travel at!
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• As electromagnetic waves all travel at the same speed and:
c = f• If a wave has a long wavelength it
must have a low frequency and vice versa a high frequency wave must have a short wavelength… f and have to always equal 300,000,000 when they are multiplied together.
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Electromagnetic waves
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t
EB
t
EEEE
o
02
22
t
EE o
or,or,
For the electric field E,For the electric field E,
i.e. wave equation with vi.e. wave equation with v22 = 1/µ = 1/µoo
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Electromagnetic waves0
2
22
t
BB o
Similarly for the magnetic fieldSimilarly for the magnetic field
i.e. wave equation with vi.e. wave equation with v22 = 1/µ = 1/µoo
oo
c1
c = 3.0 X 10c = 3.0 X 1088 m/s m/s
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Irradiance (energy per unit volume)
• Energy density stored in an electric field
• Energy density stored in a magnetic field
32 ,
2
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m
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32 ,
2
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m
JBu
oB
c
EB
32
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2 2
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c
Eu o
oB