Question

Two sources of light are said to be coherent when both give out light waves of the same

• A. Amplitude and constant phase difference
• B. Wavelength and constant phase difference
• C. Intensity and wavelength
• D. Constant phase difference and speed

Answer 1

The correct option is B

Wavelength and constant phase difference

Coherent sources:

1. When the two sources have a constant phase difference and the same frequency, the sources are called coherent sources.
2. The speed of the light can be expressed as follows:

$c=v\lambda$

Where, $c$ is the speed of the light, $v$ is the frequency, and $\lambda$ is the wavelength.

3. Since the speed of the light is constant, and the frequency of the coherent sources is also constant, the wavelength of the sources must be the same.

Hence, the light waves must have the same wavelength and constant phase difference in order to be coherent.

Therefore, option (B) is correct.