Electromagnetic radiation (EMR) is any form of radiant energy that propagates as a transverse wave, including visible light, infrared, ultraviolet, X-rays and radio waves. EMR is characterized by its wavelength or frequency. The EMR spectrum ranges from gamma rays to radio waves, divided into regions including infrared, visible light and ultraviolet. Visible light has wavelengths from 400-700 nm and is observed as different colors due to the wavelengths absorbed and transmitted by an object when illuminated with white light.

1. Electromagnetic Radiation
(EMR)
Prepared by : Museera Sardar

2. Spectroscopy
The study of interaction of electromagnetic radiation (EMR) with material (atom
or molecule )
Radiation
Energy travelling from one place to another.
Electromagnetic Radiation :(EMR)
Any form of radiant energy that is propagated as a transvers wave and vibrate
perpendicular and imparts wave motion to the radiation .

3. Terms Related with EMR
1. Wave Length
The distance between two consecutive crust or trough. OR The distance of one
complete cycle.
Unit:m, cm, nm, pm, A`
Represented by: λ
2. Frequency
The number of vibration or cycle completed per second is called frequency.
Represented by: v (n`u )
Unit: s−1 or HZ

4. 3. Wave number
The reciprocal of wavelength is called wave number or The number of waves in a
unit length or distance per cycle.
Represented by: v bar . V bar = 1/ λ
Unit: m−1, cm−1, nm−1, A`−1
4. Energy
EMR posses a certain amount of energy .The energy of ultimately indivisible unit of
radiation called the photon.
The wavelength unit preferred for Uv and visible region of spectrum is nanometer
while the unit μm is preferred for infrared region.

5. EMR Spectrum
EMR are arbitrary breakdown into different region on the basis of λ, v bar or v.
This is called EMR spectrum.
Figure 1 EMR spectrum

6. From above spectrum it is clear that Uv is divided into two:
The near Uv and near IR means that they are near to visible region while the far IR and far
Uv mean that they are far from visible region.
UV
IR

7. Visible Region
• Visible region range from 400-800nm
• It is consist of 7colors: VIBGYOR
How dose we see colors?
We see objects color because they transmit only a portion of the spectrum of
white light when illuminated by white light .
When polychromatic light (white light ) which contain the whole spectrum of
wavelengths in the object, The visible region passes through an object, The object
absorbs certain of the wavelength, leaving the unabsorbed wavelength to be
transmitted.

8. These residual transmitted wavelength are seen as a color. This color is
complementary to the absorbed color.
Some color which are absorbed and transmitted (complementary color) are given
below in in table 1.

9. Λ(nm) Absorbed Color Transmitted
(complimentary)
380 - 450 Violet Yellow Green
450 - 495 Blue Yellow
495 - 570 Green Violet
570 - 590 Yellow Blue
590 - 620 Orange Green Blue
620 - 750 Red Blue Green