Assignment Problems

Assignment Problem

1. Monochromatic light emitted by a broad source of wavelength 580 nm, falls normally on two plates of glass enclosing a wedge shaped film. The plates touch at one end and are separated at a point 15 cm from that end by a wire of 0.05 mm diameter. Find the fringe width.

(Ans. β = 8.7 × 10-4 m) 

2. Two pieces of plane glass are placed together with a piece of paper between the two at one edge. Find the angle in seconds of the wedge shape air film between the plates, if on viewing the film normally with monochromatic light of wavelength 480 nm, β = 0.0555 cm

(Ans. = 432 × 10-6 radian = 1'29")

3. Fringes of equal thickness are observed in a thin glass wedge of refractive index 1.52. The fringe spacing is 1 mm and wavelength of light is 589.3 nm. Calculate the angle of wedge in seconds of arc. 

(Ans. = 40 seconds of arc) 

4. In a Michelson's interferometer 200 fringes cross the field of view when the movable mirror is displaced through 0.0589 mm. Calculate the wavelength of monochromatic light used.

(Ans. = 589 × 10-9m = 589 nm) 

5. The movable mirror of Michelson's interferometer is moved through a distance of 0.02603 mm. Find the number of fringes shifted across the cross-wire of eyepiece of the telescope, if a wavelength of 520.6 nm is used.

(Ans. N=100) 

6. When a thin film of glass of refractive index 1.5 is interposed in the path of one of the interfering beams of the Michelson's interferometer, a shift of 30 fringes of sodium light is observed across the field of view. If the thickness of the air film is 0.018 mm, calculate the wavelength of the light used.

[Hint. 2(n-1) t = m λ]

(Ans. 600 × 10-9 m) 

7. A transparent film of glass of refractive index 1.5 is introduced normally in the path of he interfering beams of Michelson's interferometer which is illuminated with light of wavelength 480 nm. This causes 500 dark fringes to sweep across the field. Determine the thickness of the film.

(Ans. 0.00024 m)