1) A screen that is 1.0m wide is 2.0m away from a pair of slits illuminated by 6

Question

1) A screen that is 1.0m wide is 2.0m away from a pair of slits illuminated by 633-nm
light, with the screen centered between the slits. Find the highest-order bright
fringe that will appear on the screen if the slit spacing is (a) 0.10mm and (b)
10µm.

2) Light of wavelength 589 nm is incident on a single slit that is 0.720mm wide, and
the resulting diffraction pattern is observed on a screen 2.00m away. What is the
distance between the two dark fringes on either side of the central bright fringe?

3) While driving at night, your pupils dilate to 3.1mm diameter. An oncoming car has
two headlights spaced 1.5m apart. If your vision were diffraction limited, what
would be the greatest distance at which you could see the two headlights
distinctly? Assume the headlights emit light at wavelength 550 nm.

4) A tanker ship spills oil (n=1.40) into the sea. Looking at this disaster from a
helicopter overhead, what predominant wavelength of visible light do you see if
the oil is 390nm thick?

Explanation / Answer

1) = 633 nm ; D = 2 m ; W = 1 m

a) d = 0.1 mm

Fringe width = D / d = 12.66 mm.

Let there be n bright fringes. Therefore dark fringes in between them = n-1

(2n-1)* 12.66 mm < 500 [1 m screen placed mid way]

n = 20.

b) d = 10m

Fringe width = 126.6 mm

Similarly as above, n = 2.

2) Distance between dark on either side of central bright = Central maxima

= D/a [a = slit opening]

= 1.636 mm

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