Question

Light with a wavelength of 626 nm passes through a slit 7.74 μm wide and falls on a screen 1.75 m away.

Find the linear distance on the screen from the central bright fringe to the first bright fringe above it. ________cm

Answer 1

first bright fringe will be half way between first and second dark fringe.

distance of first dark fringe from central bright fringe=lambda*D/a

where lambda=wavelengh=626 nm=626*10^(-9) m

D=distance of the screen=1.75 m

d=slit width=7.74 um=7.74*10^(-6) m

then distance of first dark fringe=626*10^(-9)*1.75/(7.74*10^(-6))=0.14154 m

distance of second dark fringe=2*626*10^(-9)*1.75/(7.74*10^(-6))=0.28308 m

then distance of first bright fringe=(0.14154+0.28308)/2=0.21231 m=21.231 cm