Question

A plane wave of monochromatic light falls normally on a uniform thin film of oil which covers a glass plate. The wavelength of source can be varied continuously. Complete destructive interference is observed for λ = 5000Ã… and λ = 1000 Ã… and for no other wavelength in between. If μ of oil is 1.3 and that of glass is 1.5, the thickness of the film will be  

Solution

Correct option is

 

In this case, both the rays suffer a phase change of 180o and the conditions for destructive interference is   

                       

                       

  

               

SIMILAR QUESTIONS

Q1

In Young’s double-slit experiment, the slits are illuminated by monochromatic light. The entire set-up is immersed in pure water. Which of the following act cannot restore the original fringe width?

Q2

Blue light of wavelength 480 nm is most strongly reflected off a thin film of oil on a glass slab when viewed near normal incident. Assuming that the index of refraction of the oil is 1.2 and that of the glass is 1.6, what is the minimum thickness of the oil film (other than zero)?

Q3

The slits in a double-slit interference experiment are illuminated by orange light (λ = 60 nm). A thin transparent plastic of thickness t is placed in front of one of the slits. The number of fringes shifting on screen is plotted versus the refractive index μ of the plastic in graph shown in fig. The value of t is

                                                  

Q4

In a YDSE with identical slits, the intensity of the central bright fringe is . If one of the slits is covered, the intensity at the same point is

Q5

The maximum intensity in Young’s double-slit experiment is I0. Distance between the slits is d = 5λ, where λ is the wavelength of monochromatic light used in the experiment. What will be the intensity of light in front of one of the slits on a screen at a distance D = d?       

Q6

Two identical coherent sources are placed on a diameter of a circle of radius R at separation x (<< R) symmetrical about the centre of the circle. The sources emit identical wavelength λ each. The number of points on the circle of maximum intensity is (x = 5λ).  

Q7

In Young’s double-slit experiment  (d = distance between slits, D = distance of screen from the slits). At a point P on the screen, resulting intensity is equal to the intensity due to the individual slitI0. Then, the distance of point P from the central maximum is (λ = 6000 Ã…)

Q8

To produce a minimum reflection of wavelength near the middle of visible spectrum (550 nm) how thick should a coating of MgF(μ = 1.38) be vacuum-coated on a glass surface?   

Q9

A thin film of refractive index 1.5 and thickness 4 × 10–5 cm is illuminated by light normal to the surface. What wavelength within the visible spectrum will be intensified in the reflected beam?

Q10

A light ray frequency v and wavelength λ enters a liquid of refractive index . The ray travels in the liquid with