Optics Answers

 (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.

   State the conditions which must be full filled if interference fringes are to be observed where two

 beams of light overlap.

        Explain how it is that these conditions are fulfilled in the interference experiment using two slits, as

        in Young s experiment.

 Draw a labeled diagram of Young's apparatus for producing and observing optical interference.

 Indicate clearly on your diagram the distances that need to be measured to enable yon to determine the wavelength of light

 An essential condition for interference to be observable between wave trains originating from

two sources is that the sources should be coherent. Explain what is meant by coherent in this text.

How did Young achieve this condition in his experiment ? 

 The driver of the stationary car can hear the frequency of the sound either directly from the alarm of the car or from a bridge ahead.

(a.) Name the phenomenon that permits the driver of the stationary car to hear the sound from the bridge.

 (b.) At what frequencies does the driver of the stationary car hear the sounds?

 (c.) The stationary car starts moving towards the bridge at a speed of 6ms~1. At what frequencies does the driver now hears the sounds? Explain why he hears beats and calculate the beat frequency