Light Wave Interference Test

1. To distinguish hill and valley one surface of optical flat is lightly pressed. Which of the following option is for the valley?

Fringes move apart

Centre of fringes is displaced

Number of fringes increases

Fringes brought closer

2. If the angle between optical flat and surface to be tested is very small, then what is the difference of separation between optical flat and surface between two similar adjacent fringes?

λ/2

λ/3

3λ/2

3. In flatness testing with interferometry, if surfaces are perfectly wrung. Then which option is correct regarding fringe pattern?

No fringe pattern

Indistinguishable pattern

Fringes are closer

Fringes are at great distance

4. Which of the following option is incorrect for flatness testing by interferometry?

Only one point contact between optical flat and surface is possible in some cases

For perfectly flat surface condition of complete interference satisfies

For checking concave or convex surface optical flat is pressed lightly

If angle between optical flat and work surface reduces, then fringe spacing decreases

5. Which of the following option is true for optical flats used in flatness testing?

Working surfaces of optical flats are cylindrical

White light source is very important in measurement by light wave interference

Optical flats are better than quartz flats

Type A optical flats has only one surface flat

6. What is the range of the diameter of optical flats?

100 to 200 mm

10 to 50 mm

50 to 100 mm

25 to 300 mm

7. What is the pattern of fringes, if an optical flat is resting on any hill?

Concentric dark and light band fringes

Straight dark fringes

Central band dark

Central band may be light or black

8. Which of the following option is correct for the given statements about interferometry applied to flatness testing?
Statement 1: If the angle between optical flat and surface is too large then there will be largely spaced fringe pattern is observed.
Statement 2: Quartz flats are very sensitive to heat.

T, T

T, F

F, F

F, T

9. Which of the following is true for quartz flats?

Have 10 % less wearing quality than optical flats

Have 10 % more wearing quality than optical flats

Have 200 to 400 % more wearing quality than optical flats

Have 200 to 400 % less wearing quality than optical flats

10. Which of the following is the incorrect condition for a perfectly flat surface when tested for interferometry?

Monochromatic light is used

For perfect flat surface alternate light and dark bands are observed

Viewing angle should be greater than 0^o

Optical flats are important in light wave measurement