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A source of light of wavelength 5000Å i...

A source of light of wavelength 5000Å is placed as shown in figure.
Considering interference of direct and reflected rays, determine the position of the
region where the fringes will be visible and calculate the number of fringes.
` .

Text Solution

Verified by Experts

The correct Answer is:
D
Interference will be obtained between
direct rays from S and reflected rays from S' (image
of S on mirror).
Since, the reflected rays will lie between region P and
Q on the screen. So, interference is obtained in this
region only. From geometry will can show that,
OP = 1.9cm and OQ = 3.9cm.
`:. PQ=2cm`
`Fringe width, omega=(lambdaD)/d = ((5000 xx 10^(-8))(200))/(2 xx 10^(-1)) cm = 0.05 cm`
Total number of fringes in the region PQ,
`N=(PQ)/omega = 2/0.05 = 40`
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Knowledge Check

  • A beam of light consisting of two wavelengths 650 nm and 520 nm is used to obtain interference fringes in a Young's double slit experiment. (a) Find the distance of the third bright fringe on the screen from the central maximum for the wavelength 650 nm . (b) What is the least distance from the central maximum where the bright fringes due to both the wavelengths coincide? The distance between the slits is 2 mm and the distance between the plane of the slits and screen is 120 cm .

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    C
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    D
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