Frequency

• Frequency is properties of waves.
• For cyclical processes such as rotation, oscillations or waves, frequency is defined as a number of cycles per unit time.
• Frequency is usually denoted by a Latin letter f or by the Greek letter ν (nu).
• The SI unit of frequency is the hertz (Hz).





• The period usually denoted by T, is the duration of one cycle, and is the reciprocal of the frequency f.

f= 1 cycle/T

Types of frequency

1. Angular frequency

• Angular frequency usually denoted by the Greek letter ω (omega)
• It is defined as the rate of change of angular displacement θ (during rotation), or the rate of change of the phase of a sinusoidal waveform.
• Angular frequency is commonly measured in radian per second (rad/s).

2. Spatial frequency

• Spatial frequency is analogous to temporal frequency, but the time axis is replaced by one or more spatial displacement axes.
• It is measured by radian per minute (rad/m).

Examples

Sound

• Sound propagates as mechanical vibration waves of pressure and displacement, in air or other substances.
• Frequency is the property of sound that most determines pitch.
• The frequencies an ear can hear are limited to a specific range of frequencies.
• The audible frequency range for humans is between 20 Hz and 20,000 Hz (20 kHz).

Light

• Visible light is an electromagnetic wave, consisting of oscillating electric and magnetic fields traveling through space.
• Frequency of the wave determines its color: 4×1014 Hz is red light, 8×1014 Hz is violet light, and between these (in the range 4-8×1014 Hz) are all the other colors of the rainbow.