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

Question

A monochromatic plane wave of speed c and wavelength λ is diffracted at a small aperture. The diagram illustrates successive wavefronts. After what time will some portion of the wavefront XY reach P ? <img class="img-fluid question-image" alt="Question" src="https://cdn.tardigrade.in/q/nta/p-awljx4vechecktha.jpg" /> (A) (3 λ /2 c) (B) (2 λ /c) (C) (3 λ /c) (D) (4 λ /c)

Tardigrade Admin · Accepted Answer

Distance between successive wave fringes is a wavelength λ . So path difference from XY to P is 3λ Time taken: (3 λ /c)

Q. A monochromatic plane wave of speed $c$ and wavelength $λ$ is diffracted at a small aperture. The diagram illustrates successive wavefronts. After what time will some portion of the wavefront $X Y$ reach $P$ ?

$\frac{3 λ}{2 c}$

$\frac{2 λ}{c}$

$\frac{3 λ}{c}$

$\frac{4 λ}{c}$

Distance between successive wave fringes is a wavelength $λ$ .
So path difference from $X Y$ to $P$ is $3 λ$
Time taken : $\frac{3 λ}{c}$

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

2c3λ​

c2λ​

c3λ​

c4λ​