If Young's interference experiment is performed using two separate identical sources of light instead of using two slits and one bulb

For constructive interference to take place between two monochromatic light waves of wavelength $\lambda$, the path difference should be

Newton postulated his corpuscular theory on the basis of

A wave front is an imaginary surface where

If the speed of red light is denoted by $V_r$ and the speed of violet light by $V_v$ then for vacuum