Question

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

• A. $\frac{3\lambda}{2c}$
• B. $\frac{2\lambda}{c}$
• C. $\frac{3\lambda}{c}$
• D. $\frac{4\lambda}{c}$

Answer 1

Answer: (C)

$\frac{3\lambda}{c}$

Answer 2

Distance between successive wave fringes is a wavelength l so path difference 3l time table : $\frac{3\lambda}{C}$