KVPY Sample Paper KVPY Stream-SX Model Paper-11

A single slit of width a is illuminated by violet light of wavelength 400 nm and the width of the diffraction pattern is measured as' y. When half of the slit width is covered and illuminated by yellow light of wavelength 600 nm, the width of the diffraction pattern is

A) the pattern vanishes and the width is zero

B) \[y/3\]

C) \[3y\]

D) \[5y\]

Correct Answer: C

Solution :

\[\sin \theta =\frac{\lambda }{d}\]

Or \[\theta =\frac{\lambda }{d}\]

\[\therefore {{\beta }_{1}}=D{{\theta }_{1}}\,=\frac{400}{d}D=y\]

And \[{{\beta }_{2}}=D{{\theta }_{2}}=\frac{600D}{d/2}=3y\]