Fig.2.6 The electric and magnetic field components of an electromagnetic wave. These components have the same wavelength, frequency, speed and amplitude, but they vibrate in two mutually perpendicular planes.

1. Unlike sound waves or water waves, electromagnetic waves do not require medium and can move in vacuum.
2. It is now well established that there are many types of electromagnetic radiations, which differ from one another in wavelength (or frequency). These constitute what is called electromagnetic spectrum (Fig. 2.7). Different regions of the spectrum are identified by different names. Some examples are: radio frequency region around 10⁶ Hz, used for broadcasting; microwave region around 1010 Hz used for radar; infrared region around 10¹³ Hz used for heating; ultraviolet region around 1016Hz a component of sun’s radiation. The small portion around 10¹⁵Hz, is what is ordinarily called visible light. It is only this part which our eyes can see (or detect). Special instruments are required to detect non-visible radiation.
3. Different kinds of units are used to represent electromagnetic radiation.

These radiations are characterised by the properties, namely, frequency (ν ) and wavelength (λ).

The SI unit for frequency (ν ) is hertz (Hz, s^–1), after Heinrich Hertz. It is defined as the number of waves that pass a given point in one second.

Wavelength should have the units of length and as you know that the SI units of length is meter (m). Since electromagnetic radiation consists of different kinds of waves of much smaller wavelengths, smaller units are used. Fig.2.7 shows various types of electro-magnetic radiations which differ from one another in wavelengths and frequencies. In vaccum all types of electromagnetic radiations, regardless of wavelength, travel at the same speed, i.e., 3.0 × 10⁸ m s^–1

(2.997925 × 10⁸ m s^–1, to be precise). This is called speed of light and is given the symbol ‘c‘. The frequency (ν ), wavelength (λ) and velocity of light (c) are related by the equation (2.5). c = ν λ (2.5)

The other commonly used quantity specially in spectroscopy, is the wavenumber (ν ). It is defined as the number of wavelengths per unit length. Its units are reciprocal of wavelength unit, i.e., m^–1. However commonly used unit is cm^–1 (not SI unit).

Fig.2.6 The electric and magnetic field components of an electromagnetic wave. These components have the same wavelength, frequency, speed and amplitude, but they vibrate in two mutually perpendicular planes.

1. Unlike sound waves or water waves, electromagnetic waves do not require medium and can move in vacuum.
2. It is now well established that there are many types of electromagnetic radiations, which differ from one another in wavelength (or frequency). These constitute what is called electromagnetic spectrum (Fig. 2.7). Different regions of the spectrum are identified by different names. Some examples are: radio frequency region around 10⁶ Hz, used for broadcasting; microwave region around 1010 Hz used for radar; infrared region around 10¹³ Hz used for heating; ultraviolet region around 1016Hz a component of sun’s radiation. The small portion around 10¹⁵Hz, is what is ordinarily called visible light. It is only this part which our eyes can see (or detect). Special instruments are required to detect non-visible radiation.
3. Different kinds of units are used to represent electromagnetic radiation.

These radiations are characterised by the properties, namely, frequency (ν ) and wavelength (λ).

The SI unit for frequency (ν ) is hertz (Hz, s^–1), after Heinrich Hertz. It is defined as the number of waves that pass a given point in one second.

Wavelength should have the units of length and as you know that the SI units of length is meter (m). Since electromagnetic radiation consists of different kinds of waves of much smaller wavelengths, smaller units are used. Fig.2.7 shows various types of electro-magnetic radiations which differ from one another in wavelengths and frequencies. In vaccum all types of electromagnetic radiations, regardless of wavelength, travel at the same speed, i.e., 3.0 × 10⁸ m s^–1

(2.997925 × 10⁸ m s^–1, to be precise). This is called speed of light and is given the symbol ‘c‘. The frequency (ν ), wavelength (λ) and velocity of light (c) are related by the equation (2.5). c = ν λ (2.5)

The other commonly used quantity specially in spectroscopy, is the wavenumber (ν ). It is defined as the number of wavelengths per unit length. Its units are reciprocal of wavelength unit, i.e., m^–1. However commonly used unit is cm^–1 (not SI unit).

Fig. 2.7 (a) the spectrum of electromagnetic radiation. (b) Visible spectrum. The visible region is only a small part of the entire spectrum