Optics Answers

A beam of parallel light is incident normally on a diffraction grating having 550 lines per mm. A

 telescope is used to observe the second order in the spectrum. Calculate the angular separation in radians of two spectra lines of wavelengths 559nm and 563nm.

 A laser is used to produce young fringes with slits separated by 0.50mm. The screen is 1.0m

     from the slits and 10 fringe separations occupy 12.5mm. What is the wavelength of the laser light?

     State the advantage of using light from a laser. 

 (a.) Diffraction and interference are phenomena exhibited by waves. State clearly the differences

     between these two phenomena.

When a thin film of transparent plastic is placed over one of the slits in Young's double slit

     experiment, the central fringe is displaced by 4.5 fringes. The refractive index of the material is 1.48

    and the wavelength of the light in air is 5.5 × 10^-7 m.

    (i.) By how much does the film increase the optical path?

    (ii.) What is the thickness of the film?

    (iii.) What would be observed if the material had a thickness of 1.00mm? Explain. 

 (i.) State the conditions necessary for two sources of light to produce interference.

    (ii.) How are these conditions satisfied in Young's double-slit experiment?

Tom and Jerry are placed at a distance of 32 cm. Between them a convex lens is placed having a focal length of 15 cm in such a way that images of both Tom and Jerry way are formed at same place. What can be the possible distance of Tom from lens?

When a 5cm plane mirror is held 0.5m from the eye the image of the mango tree in the mirror is also 5cm tall. How tall is the mango tree if it 100m from the mirror

  In one of Young's double slit experiment, two thin parallel slits S1 and Sz, distant a apart are

          illuminated with by an intermediate slit S parallel to S1 and S2 and situated at the same distance

          from each. A system of fringes is produced on a screen P, parallel to the double slit and distant D

           from it. It is discovered that N consecutive fringes of the same nature occupy a length L.

           (i.) Derive, from first principle, the expression for λ, the wavelength of the light used, in terms of

           a, D, l and N. Hence, calculate λ given that a = 2mm, D = 1m, l = 4mm, N = 12.

           (ii.) What will be the new value of L, for the same number N of fringes if the apparatus is plunged in a pool of water? (Hint: index of water= 4/3)

  Explain why it is possible to observe sound interference effects using two whistles, but not light

interference effects using two lamps, even if the dimensions of the apparatus are suitably modified.

 Describe, quoting the necessary formula how you would determine the wavelength of monochromatic light by observation of Young's fringes.