# Phase Difference

In this lesson, we shall understand the terms Phase and Phase Difference in the context of Radio Waves. In our earlier post, we had understood the classification of radio waves in different Radio Frequency Bands.

### PHASE

Phase of an electromagnetic wave is the position of the wave at a given instant of time on the sine wave form. It is expressed as 0 to 360 degrees of a circle. If the starting point of the wave is taken as being at zero amplitude its maximum amplitude would be at 90 degrees.

The wave would return to its mean position at 180 deg of phase and would reach maximum negative amplitude at 270 degrees. Finally, the wave would come back to its mean position at 360 degrees of phase.

### PHASE DIFFERENCE

Phase difference is the difference in phase between two waves. Phase difference can be obtained by phase comparison of the wave forms. Phase comparison is the comparison of phase of two radio waves. one of them is named as the reference wave and the other is called as the variable wave.

Phase difference indicates how much the variable wave is out of phase with the reference wave. Phase can be compared only between waves of same frequency and wave length. Principle of phase comparison is used in some radio navigational equipment like Automatic Direction Finder (ADF)

In this post, we have learnt about the terms Phase and Phase Difference of Radio Waves, In our next lesson, let us understand the power required for radio waves based on the Inverse Square Law of Electro-Magnetic Radiation.