Question

Sources 1 and 2 emit lights of different wavelengths whereas 3 and 4 emit lights of different intensities (but same wavelength). Coherence-

• A. Can be obtained by using sources 1 and 2
• B. Can be obtained by using sources 3 and 4
• C. Cannot be obtained by any of these sources
• D. Since contrast suffers when sources 3 and 4 are used so coherence cannot be obtained by using sources 3 and 4
  

Answer 1

The correct option is B Can be obtained by using sources 3 and 4

Different wavelengths would correspond to different frequencies, so coherence is not possible; whereas lights of different intensities can give coherence even if the contrast is poor.