Assignment no.1

GA-II (III Semester) MM:30 Attempt all questions. All carry equal marks.

Mulitiple choice questions

1. Two coherent source of light produces constructive interference when the phase difference

between them is

a) π

b) 2π

c) 3/2π

d) π/2

2. the brilliant colours in thin films of soap are due to

a) dispersion

b) diffraction

c) interference

d) scattering

3. the refracting angle of fresnel’s biprism is

a) 1/2:

b) 0:

c) 180:

d) 179:

4. A phase difference of π between two waves reaching a point is equal to the path difference of

a) λ

b) λ/2

c) 2λ

d) λ/4

5. in young’s double slit experiment if the distance between the slits is halved and the distance of

screen from the slits is doubled, then the fringe width will be

a) remain same

b) reduce to half

c) be doubled

d) increase to four time

6. the optical path difference in a wedge shaped film is

a)

b) + λ/2

c) - λ/2

d) - 3λ/4

7. the shape of the fringes obtained in wedge shaped film is

a) circular

b) straight

c) curved

d) elliptical

8. in newton’s ring experiment when drops of oil ( ) are inserted in between the plane

glass plate and the lens ( ) then

a) the rings appears to contract inwards

b) the rings appears to expand outwards

c) the rings remains unchanged

d) the rings disappear

9. interference is possible by

a) longitudinal waves

b) transverse waves

c) by both waves

d) by none of waves

10. newton’s rings are

a) circular and localized in the film

b) circular and formed at infinity

c) elliptical and localized in the film

d) hyperbolic and at infinity

short answer type questions

11. give the relation between phase difference & path difference and time difference?

12. Define coherent and incoherent sources?

13. Write conditions to obtain a sustained interference pattern?

14. Show interference by fresnel’s biprism ( only diagram)?

15. What is the path difference between two interfering waves by method of division of amplitude?

( give only expression & define symbols).Is it same in both reflected or transmitted part?

16. Write the conditions of bright and dark fringes in transmitted part as well as in reflected part?

( give only expression & define symbols).

17. Give examples of interference obtained by division of amplitude?( at least two)

18. Draw newtons rings in reflected part & write the diameter for nthbright & dark ring?

19. Write short note on colours due to thin films?

20. Write down the statement of stokes law?

21. Explain why newtons rings are the fringes of equal thickness?

22. What should be the order of thickness of the film so that it may appear coloured in white light?

Numericals

23. A planoconvex lens of radius of curvature 88 cm is placed on a plane glass plate, newton’s rings

are formed with mercury green light (λ=5460A:). find the differences in the square of diameter

of ten fringes.

24. Two coherent beams of intensities 1.6 & 0.4 unit produces a resultant intensity of 0.6 unit at a

certain point. Calculate the minimum phase difference with which the beams reach the point.

25. when a thin sheet of mica of thickness 6.3X10-6 m is introduced in the path of one of the

interfering beams, the central fringe shifts to a position of sixth bright fringe. λ =5460A:, find the

refractive index of the sheet.