A monochromatic plane wave of speed c and wavelength $λ$ is diffracted at a small aperture. The diagram illustrates successive wavefronts (vibrating in the same phase). After what time will some portion of the wavefront $XY$ reach $P$ ?

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TestHub · Accepted Answer

This distance between the 2 successive lines (wavefronts) is $λ$ . This is for both the straight and curved lines.

So, wavefront XY is separated by a distance of $3 λ$ from the wavefront that has reached point P.

Distance that needs to be traveled $= 3 λ$

Speed of light $= c$

Speed = Distance/Time

Time = distance/speed $= \frac{3 λ}{c}$

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