Define angular frequency, wave number and wave vector.

Explanation

(i) The number of cycles (or revolutions) per unit time is called angular frequency. Angular frequency, `omega =(2pi)/T = 2 pi f` (unit is radian/ second).
(ii) The number of cycles per unit distance or number of waves per unit distance is called wave number.
(iii) In two, three or higher dimensional case, the wave number is the magnitude of a vector called wave vector. The points in space of wave vectors are called reciprocal vectors, `vec(k)`.
Dimensional of `vec(k)` is `L^(-1)`.