For observing sustained interferencr with good contrast, which of the following option are correct?
(i) The sources must be coherent i.e. the phase difference must remain constant.
(ii) The frequencies, wavelengths and amplitudes of interfering waves must be equal and light must be monochromatic.
(iii) The source must be close to each other and must be narrow.
(iv) If the interfering beams are polarised, they must be in the same state of polarisation.

Options

A. (i), (ii)
B. (ii), (iii), (iv)
C. (i), (ii), (iii)
D. all

Answer

D