A set of narrow vertical slits is located a distance D from a screen. The slits

Question

A set of narrow vertical slits is located a distance D from a screen. The slits are equally spaced and have the same width. The intensity pattern in the figure is observed when light from a laser passes through the slits, illuminating them uniformly. The screen is perpendicular to the direction of the light. Data: Distance to the screen = 2.59 m, wavelength of light = 520 nm, Distance between tick marks on the intensity figure = 1.40 cm. What is the spacing between the slits? 9.816 times 10^-5 m Calculate the width of the slits. 1.963 times 10^-5 m If the slit separation is increased by a factor of 2, what would be the distance between the principal peaks on the screen? How does the slit separation affect the diffraction pattern?

Explanation / Answer

Answer for Double Slit -

the diffraction pattern spread out when slits becomes narrower.

Other Way Around (Diffraction pattern spreads out)

Here is why: Each band of light in the diffraction pattern is caused by constructive interference. Constructive interference occurs when
n / d = x / L
where
is the wavelength of the light,
d is the separation of the slits
n is the order of maximum observed (central maximum is n = 0),
x is the distance between the bands of light and the central maximum (also called fringe distance), and
L is the perpendicular distance from the slits to the screen (or retina of your eye).

Choose a given band of light to observe. It has some definite value for n. Now decrease separation d. Since n, , and L are constant, x must increase, where x is the distance from the central maximum to the band we are observing. (The central band is the band of light directly under the two slits, the band located on the screen directly across from the center of the two slits.) Hence the diffraction pattern spreads out.

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