EASY
JEE Main
IMPORTANT
Earn 100

A thin film of liquid is held in a horizontal circular ring, with air on both sides of the film. A beam of light at wavelength 620 nm is directed perpendicularly onto the film, and the intensity P of its reflection is monitored. The figure gives intensity l as a function of time t, the horizontal scale is set by ts=20.0 s. The intensity changes because of evaporation from the two sides of the film. Assume that the film is flat and has parallel sides, a radius of 1.2 cm, and an index of refraction of 1.33 . Also assume that the film's volume decreases at a constant rate. Find that rate.

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Important Questions on Interference

MEDIUM
JEE Main
IMPORTANT
A double-slit arrangement produces interference fringes for sodium light (λ=589 nm) that has an angular separation of 3.50×10-3 rad. For what wavelength would the angular separation be 6.0% greater?
EASY
JEE Main
IMPORTANT

In the figure (a), a beam of light in material 1 is incident on a boundary at an angle of 30°. The extent to which the light is bent due to refraction depends, in part, on the index of refraction n2 of material 2. Figure (b) gives the angle of refraction θ2 versus n2 for a range of possible n2 values, from na=1.40 to nb=2.00. What is the speed of light in material 1 ?

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(a)                                                                (b)

EASY
JEE Main
IMPORTANT
Suppose that Young's experiment is performed with blue green light of wavelength 410 nm. The slits are 1.20 mm apart, and the viewing screen is 5.40 m from the slits. How far apart are the bright fringes near the center of the interference pattern?
EASY
JEE Main
IMPORTANT
White light is sent downward onto a horizontal thin film that is sandwiched between two materials. The indexes of refraction are 1.80 for the top material, 1.65 for the thin film, and 1.50 for the bottom material. The film thickness is 5.00×10-7 m of the visible wavelengths (400 nm to 700 nm) that result in fully constructive interference at an observer above the film, which is the (a) longer and (b) shorter wavelength? The materials and film are then heated so that the film thickness increases. (c) Does the light resulting in fully constructive interference shift toward longer or shorter wavelengths?
EASY
JEE Main
IMPORTANT
In a double-slit experiment, the distance between slits is 5.0 mm and the slits are 1.8 m from the screen. Two interference patterns can be seen on the screen, one due to light of wavelength 480 nm, and the other due to light of wavelength 600 nm. What is the separation on the screen between the third-order (m=3) bright fringes of the two interference patterns?
MEDIUM
JEE Main
IMPORTANT

In the below figure, a light ray is incident at angle θ1=55° on a series of five transparent layers with parallel boundaries. For layers 1 and 3L1=20 μmL3=25 μmn1=1.6 and n3=1.45.

(a) At what angle does the light emerge back into the air on the right?

(b) How much time does the light take to travel through layer 3?

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MEDIUM
JEE Main
IMPORTANT

In the following figure, assume that two waves of light in the air, of wavelength 585 nm, are initially in phase. One travels through a glass layer of the index of refraction n1=1.60 and thickness L. The other travels through an equally thick plastic layer of the index of refraction n2=1.50.

(a) What smallest value L should have if the waves are to end up with a phase difference of 5.65 rad?

(b) If the waves arrive at some common point with the same amplitude, is their interference fully constructive, fully destructive, intermediate, but closer to fully constructive or intermediate but closer to fully destructive?

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EASY
JEE Main
IMPORTANT

In the two-slit experiment from the given figure, let angle θ be 30.0°, the slit separation be 4.24 μm, and the wavelength be λ=500 nm.

(a) What multiple of λ, gives the phase difference between the waves of rays r1 and r2, P on the distant screen?
(b) What is the phase difference in radians?
(c) Determine where, in the interference pattern point P lies by giving the maximum or minimum on which it lies, or the maximum and minimum between which it lies.

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