Engineering Metrology Multiple Choice Questions on “Wavelength Standard”.
1. Which of the following is not correct about wavelength standard?
a) Wavelength of monochromatic light is an invariable unit of length
b) Wavelength standard is a physical standard
c) It is a reproducible standard
d) It is a natural unit of length
Answer: b
Clarification: Wavelength standard need not be preserved as it is not a physical one. This is an advantage of wavelength standard over others.
2. What is the error in a reproduction of wavelength standard?
a) 1 part in 100 million
b) 2 parts in 50 million
c) 2 parts in 50 million
d) 1 part in 50 million
Answer: a
Clarification: Wavelength standard is reproducible and error of reproduction is very less i.e. only 1 part in 100 million.
3. Which of the following is the most suitable for wavelength standard?
a) Cadmium 114
b) Krypton 86
c) Mercury 198
d) Any monochromatic light
Answer: b
Clarification: If used in a hot cathode discharge lamp then It is the most suitable element. Temperature should be maintained at 64oK.
4. Which colour radiation of krypton 86 is selected for measurement?
a) Yellow
b) Green
c) Orange
d) Blue
Answer: c
Clarification: Orange radiation of Kr 86 is selected for measurement. Orange-red line of Kr 86 is produced under some specific conditions like at the temp of 64oK.
5. Which of the following option is correct for given statements about wavelength standard?
Statement 1: Gas lasers produce 1000 times more intense light than others.
Statement 2: Lasers cannot be used for some interferometers like Pitter-NPL gauge interferometer.
a) T, F
b) F, T
c) F, F
d) T, T
Answer: d
Clarification: Working of Pitter-NPL gauge interferometer is based on 3 or 4 different wavelengths. Laser contains only a single wavelength.
6. Which of the following is not an advantage of gas laser?
a) Bigger size
b) Highly monochromatic light
c) Produce intense light
d) Enormous path difference between interference fringes
Answer: a
Clarification: Bigger size, high cost and effect of temperature and vibration on wavelength, these are the disadvantages of laser.
7. Which of the following option is correct for the given statements?
Statement 1: End and wavelength standards can be compared without any mechanical movement.
Statement 2: Indirect comparison of line standard and wavelength standard involves movement.
a) Only statement 1 is true
b) Only statement 2 is true
c) Both the statements are true
d) Both the statements are not true
Answer: c
Clarification: Comparison of end and wavelength standard does not involve any mechanical movement. Terminal surfaces of end standard can be used as optical reflectors. But in comparison of line and wavelength standard, movement like movement of carriage are involved.
8. What is the path difference between interference fringes, when krypton 86 is used?
a) 500 mm
b) 800 mm
c) 1000 mm
d) 1200 mm
Answer: b
Clarification: Next to laser, Krypton 86 enables maximum path difference i.e. 800 mm between fringes.
9. Which of the following option is correct about wavelength standard?
a) Wavelength does not depend upon the amount of isotope impurity
b) Solid state lasers having high intrinsic noise can be used to study new lines
c) Krypton 86 is produced by neutron bombardment of gold
d) Cadmium 114 is the secondary international length standard
Answer: d
Clarification: Wavelength depends upon the impurity of isotopes. Mercury 198 is produced by neutron bombardment of gold. Cadmium is the only natural material which can produce an almost symmetrical spectral line.