Interference. Laser light of wavelength 628 nm illuminates 2 narrow slits separa

Question

Interference. Laser light of wavelength 628 nm illuminates 2 narrow slits separated by distance d. The pattern observed on the screen shows a very bright spot at the center of the screen, with a series of spots spaced almost evenly on both sides of the center, as shown. If the distance on the screen from the center bright spot to the third bright spot (on either side) is 3.00 cm, which choice best represents the separation, d, between the slits? Suppose that the slit separation, d, is increased by 20%, and no other change is made. Which choice best represents what happens to the pattern on the screen? The spacing between the centers of the bright spots increases. same, but the intensity of each bright spot increases. The spacing between the centers of the bright spots decreases. same, but the intensity of each bright spot decreases.

Explanation / Answer

path difference d*sintheta = m*lambda

for small angles sintheta = tantheta = = y/R

R = slit - screen distance

y = distance from the center bright to the third bright

y = m*R*lambda/d

0.03 = 3*2.4*628*10^-9/d

d = 0.15 mm <<<<-----answer

OPTIOn C

++++++++++++++++++++++++++++++

13)

y2/y1 = d1/d2

d2 = d1 + 0.2*d1

d2 = 1.2*d1

y2/y1 = 1/1.2

y2 = y1/1.2

y2 < y1

space between the centers of the bright spots decreases

OPTION C

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