120.

What are the characteristics of waves?

The following parameters are used to characterize these waves:

(i) Wavelength: It is defined as the distance between two adjacent crests or troughs of the wave. It is denoted by lambda (λ). It is generally expressed in meters; Angstroms (Å) or nanometres (nm).
1 Å = 10^-10m
1 nm = 10^-9 m

(ii) Frequency: It is defined as number of waves which pass through a given point in one second. It is denoted by v (nu) and is measured in cycles per second (cps) or simply reciprocal seconds (sec^-1). It is also expressed in terms of Hertz (Hz).



It is inversely proportional to the wavelength.


(iii) Velocity: The distance travelled by the wave in one second is called the velocity of the wave. It is denoted by c and is equal to the product of wavelength and frequency.
c =vλ

The units of velocity are ms^-1 or cm s^-1.
Light and all other types of electromagnetic radiations travel through space with the same velocity i.e. 3 x 10^-8 ms^-1.

(iv) Amplitude: The height of the crest or the depth of the trough or distance of maximum displacement is called amplitude. It is denoted by a. It determines the density or brightness of a beam of light.

(v) Wave number: It is defined as the number of wavelengths per unit of length and is equal to the inverse of wavelength expressed in centimeters. It is denoted by ⊽ cm^-1 or in^-1.
                                                    ...(1)
But                          
or                                                ...(2)
  From (1) and (2),
                            
or