Question

Why coherent sources are essential for observable interference?

Answer 1

Step 1: Coherent source

1. Sources that emit a light wave of the same frequency are called coherent sources.
2. A coherent source is necessary to observe certain optical phenomena such as interference.
3. Coherent sources have the same:

(i). phase and amplitude

(ii). constant phase difference

(iii). wavelength and intensity

(iv). speed

Step 2: Coherent sources are essential for interference as,

1. In case of interference, it is necessary to ensure that the position of minima and maxima do not change with time.
2. To ensure this, the sources must have the same phase, amplitude, and constant phase difference.
3. This is only possible if we use coherent sources.
4. If we use two different sources, it is not possible to have the same phase, phase difference, and amplitude for them.
5. Hence, coherent sources are essential for observable interference.