Ascreen is placed 50cm from a single slit illuminated with 690nm light. if the distance between the first and third dark fringes in the diffraction pattern is 3mm.
a) find the width of the slit
used w=(2\lambdal)/d to get 500 mm
b) find the width of the central bright fringe using w=(2\lambdal)/d .

Explanation:

a ) Distance of screen (D) = 50 X 10⁻²

Wavelength of light λ = 690 x 10⁻⁹

d  = width of slit

Distance between first and third dark fringe = 2 x fringe width

= 2 x λD/d = 3 x 10⁻³

d = 2 x 690 x 10⁻⁹ x 50 x 10⁻² /3 x 10⁻³ =  0.23 mm

b ) Width of central bright fringe = 2 λD/d

2 x 690 x 10⁻⁹ x 50 x 10⁻² /23 x 10⁻⁵ m

= 3 mm.

which statement about this sum is true? −245+2.7

1 - wave length

2 - amplitude

3 - crest

4 - trough

explanation:

duh.