Question

If two light waves are coherent: a) their amplitudes are the same b) their phase difference is constant c) their frequencies are the same d) their wavelengths are the same e) the difference in their frequencies is constant

Answer 1

Answer:

The correct answer is option 'b' and 'c' :

1) Their phase differences are constant

2)Their frequencies are same.

Explanation:

Two light waves are said to be coherent if they have a constant phase difference between.A condition that is attached inherently to this definition is the waves must have the same frequency.

For 2 waves

$y_{1}=A_{1}sin(\omega t+kx)\\\\y_{2}=A_{2}sin(\omega t+kx+\phi )$

Are coherent as they have a constant phase difference $\phi$ even if they have different Amplitudes.

The phase difference in the above two waves are

$\delta =(\omega t+kx+\phi )-(\omega t+kx)\\\\\delta =\phi$

Thus they must have same frequency.