EASY
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In a YDSE set up in air, the fringe width is w. If the whole set up is now immersed inside a liquid of refractive index 2, the fringe width will become wk, find k.

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Important Questions on Wave Optics

HARD
In the Young's double slit experiment using a monochromatic light of wavelength λ , the path difference ( in terms of an integer n ) corresponding to any point having half the peak intensity is
HARD
Electrons accelerated from rest by an electrostatic potential are collimated and sent through a Young's double slit experiment. The fringe width is ω. If the accelerating potential is doubled, then the width is now close to:
MEDIUM
In Young's double-slit experiment, in an interference pattern, the second minimum is observed exactly in front of one slit. The distance between the slits is d and the distance between source and screen is D. The wavelength of the light source used is
MEDIUM
In Young’s double-slit experiment, the distance between the two identical slits is 6.1 times larger than the slit width. Then the number of intensity maxima observed within the central maximum of the single-slit diffraction pattern is :
MEDIUM
In a Young's double slit experiment, the slits are placed 0.320 mm apart. Light of wavelength λ=500 nm is incident on the slits. The total number of bright fringes that are observed in the angular range -30oθ30o is:
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Using monochromatic light of wavelength λ , an experimentalist sets up the Young's double slit experiment in three ways as shown.
If she observes that y = β , the wavelength of light used is :

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HARD
In a Young's double slit experiment, slits are separated by 0.5 mm, and the screen is placed 150 cm away. A beam of light consisting of two wavelengths, 650 nm and 520 nm, is used to obtain interference fringes on the screen. The least distance from the common central maximum to the point where the bright fringes due to both the wavelengths coincide is:
MEDIUM
The figure shows a Young's double slit experimental setup. It is observed that when a thin transparent sheet of thickness t and refractive index μ is put in front of one of the slits, the central maximum gets shifted by a distance equal to n fringe width. If the wavelength of light used is λ then t will be:
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MEDIUM
In Young's double slit experiment, the two slits are illuminated by light of wavelength 5890  and the angular distance between the fringes obtained on the screen is 0.2o. If the whole apparatus is immersed in water then the angular fringe width will be, if the refractive index of water is 43.
MEDIUM
The distance between two coherent sources is 1 mm. The screen is placed at a distance of 1 m from the sources. If the distance of the third bright fringe is 1.2 mm from the central fringe, the wavelength of light used is
HARD
In Young's double-slit experiment, the distance between slits and the screen is 1 m and monochromatic light of wavelength 600 nm is being used. A person standing near the slits is looking at the fringe pattern. When the separation between the slits is varied, the interference pattern disappears for a particular distance d0 between the slits. If the angular resolution of the eye is 160°, then the value of d0 is close to
HARD
Consider a Young's double slit experiment as shown in figure. What should be the slit separation d in terms of wavelength λ such that the first minima occurs directly in front of the slit (S1) ?

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EASY
In a double slit experiment, when light of wavelength 400 nm was used, the angular width of the first minima formed on a screen placed 1 m away was found to be 0.2°. What will be the angular width of the first minima, if the entire experimental apparatus is immersed in water? μwater=43
EASY
Young's double slit experiment is first performed in air and then in a medium other than air. It is found that 8th bright fringe in the medium lies where 5th dark fringe lies in air. The refractive index of the medium is nearly
MEDIUM
In a double slit experiment, when a thin film of thickness t having refractive index μ is introduced in front of one of the slits, the maxima at the centre of the fringe pattern shifts by one fringe width. The value of t is (λ is the wavelength of the light used):
HARD
In a Young’s double slit experiment, the separation between the slits is 0.15 mm . In the experiment, a source of light of wavelength 589 nm is used and the interference pattern is observed on a screen kept 1.5 m away. The separation between the successive bright fringes on the screen is:
MEDIUM
In a double – slit experiment, at a certain point on the screen the path difference between the two interfering waves is 18th of a wavelength. The ratio of the intensity of light at that point to that at the center of a bright fringe is:
MEDIUM
In a double-slit experiment, the two slits are 1 mm apart and the screen is placed 1 m away. A monochromatic light of wavelength 500 nm is used. What will be the width of each slit for obtaining ten maxima of double-slit within the central maxima of a single-slit pattern?
MEDIUM
In a Young's double slit experiment slit separation 0.1 mm, one observes a bright fringe at angle 140 rad by using light of wavelength λ1. When the light of wavelength λ2 is used a bright fringe is seen at the same angle in the same set up. Given that λ1 and λ2 are in visible range 380 nm to 740 nm, their values are:
EASY
In Young's double slit experiment the separation d between the slits is 2 mm, the wavelength λ of the light used is 5896  and distance D between the screen and slits is 100 cm. It is found that the angular width of the fringes is 0.20°. To increase the fringe angular width to 0.21o (with same λ and D) the separation between the slits needs to be changed to