ELECTROMAGNETIC RADIATION
ELECTROMAGNETIC RADIATION
Light is a form of energy called electromagnetic energy,
which travels in form of waves. It means the electromagnetic energy or
radiation defines the wave nature of light. Other types of electromagnetic
waves are radio, microwave, infra-red (heat), ultraviolet (UV), X-ray & Gamma
ray radiation. Here light refers to visible light white, which consists of seven
colors added together. The seven colors are Violet, Indigo, Blue, Green,
Yellow, Orange and Red (VIBGYOR).
WAVE : We can
differentiate waves by their wavelengths. Wavelength is the distance between
two crests. Crest is the highest point of a wave. The trough is the lowest
point of a wave. Amplitude is the highest value of the wave and Frequency is
the number of waves in a given period of time. Or we can define frequency
mathematically as –
fλ = c …………(i)
Where, f = frequency
λ =
wavelength
c = speed
of light in vacuum
It means, from the formula we can say that frequency and
wavelength of an electromagnetic wave is inversely proportional. The shorter
the wave length and the greater the frequency.
Relation between Energy and Frequency and Wavelength :
We know that the energy of a photon is, E = hf
Where, h = Plank’s constant= 6.626176 x 10-34 joule-seconds.
f =
frequency
putting equation (i) in this equation –
E = hc/λ
It means, the shorter the wavelength and the greater the
frequency, the higher the energy.
THE ELECTROMAGNETIC SPECTRUM
The electromagnetic spectrum is the range of frequencies of electromagnetic
radiations or waves and their respective wavelengths and photon energies. By
seeing the EM spectrum we can differentiate between every EM waves according to
their frequencies, respective wavelengths and photon energies.
HISTORY : In 1800 William Herschel discovered infrared
radiation. The next year, Johann Ritter discovered ultraviolet radiation. Then
Maxwell’s equations predicted an infinite number of frequencies of
electromagnetic waves. In this way the electromagnetic spectrum is build.
VISIBLE LIGHT SPECTRUM
COLOR
|
WAVELENGTH (nm)
|
FREQUENCY (THz)
|
PHOTON ENERGY (eV)
|
Violet
|
380-450
|
668-789
|
2.75-3.26
|
Blue
|
450-495
|
606-668
|
2.50-2.75
|
Green
|
495-570
|
526-606
|
2.17-2.50
|
Yellow
|
570-590
|
508-526
|
2.10-2.17
|
Orange
|
590-620
|
484-508
|
2.00-2.10
|
Red
|
620-750
|
400-484
|
1.65-2.00
|
There is one more color in Rainbow that is Indigo. The frequency
of Indigo is 425-450 nm.
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