This Portion of Electrical andElectronic Measurements and Measuring instruments contains Units, Systems, Dimensions and Standards MCQs (Multiple Choice Questions and Answers) / Objective Type Questions and Answers.

 

This Section covers below lists of topics.

  1. Units, Absolute Units, Fundamental and Derived Units
  2. Dimension, Dimension of Mechanical Quantities
  3. CGS System of Units
  4. Relationship between Electrostatic and Electromagnetic System of units
  5. MKS System
  6. SI Units
  7. Supplementary Units
  8. Absolute measurement of Currents and Resistance
  9. Standards and their Classification, Standards for mass and length
  10. Atomic Frequency and Time Standards
  11. Temperature Standards
  12. Luminous intensity standards
  13. Electrical Standards
  14. Emf Standards
  15. Resistance, Current, Inductance , Capacitance Standards

 

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1. A coherent system of units is to be evolved which has N kinds of quantities to evaluate and M independent physical quantities expressing relationship between them, we can independently choose the sizes of units of :

  • N+M quantities
  • N-M quantities
  • N quantities
  • M quantities

2. The units whose sizes cannot be chosen independently are called :

  • Derived units
  • Fundamental units
  • Absolute units
  • Auxiliary fundamental units.

3. The dimension of inductance in CGS s system are :

  • [ԑL-1T 2]
  • [ԑ-1 ML-1 T 2]
  • [ԑ-1LT -2]
  • [ԑ-1 L-1 T 2]

4. The dimension of resistance CGS e.m. System are :

  • [µ -1LT -1]
  • [µ -1 MLT -1]
  • [µ LT -1]
  • [µ LT -2]

5. The base units in SI system are

  • Metre, kilogramme, second
  • Metre, kilogramme, second, ampere
  • Metre, kilogramme,second, ampere, Kelvin, candela, mole
  • Metre, kilogramme, second, ampere, Kelvin, candela

6. The symbole nm stands for :

  • newton metre
  • nano metre
  • nano milli
  • number of moles.

7. In measuring the absolute value of ampere using Rayleigh’s balance, the value of gravitational constant g must be accurately known because :

  • The expression for the force is in Newton and weights used in counterbalancing the force are in kg
  • Value of g is different at different places
  • Corrections have to be made for the weight of moving coil
  • None of the above.

8. In Lorenz method for absolute measurements of ohm, two measurements are made one with current in one direction and the other with current in the opposite direction. This is done to :

  • eliminate the effect of thermal emfs
  • eliminate the effect of earth’s magnetic field
  • eliminate the effect of both thermal emfs and earth’s magnetic field
  • eliminate the effect of both temperature on coil and disc.

9. The international standard of length is defined in terms of :

  • Length of earth’s meridian passing through paris
  • Distance between two lines engraved on a platinum-iridium bar
  • Wavelength in vaccume, of radiation of krypton -86 atom in its two specified transitions
  • None of the above.

10. The most stable primary atomic standard for frequency is :

  • Caesium beam standard
  • Hydrogen maser standard
  • Quartz standard
  • Rubidium vapour standard.

11. Caseium beam standard is normally used primary atomic standard for frequency because :

  • Caesium beam standard has an accuracy 3 parts in 1012 , has short term stability , low drift and small size.
  • Hydrogen master standard, though it the most stable frequency source but has a large size.
  • Quartz crystal’s operating frequency changes with change in load capacitance and also the drift in frequency is asymptotic with time
  • All the above.

12. The disadvantage of atomic standards are :

  • Their accuracy is lower than that of standards based upon astronomical measurements
  • The time taken for measurements is long
  • The results obtained with atomic standards are not uniform
  • None of the above.

13. The maximum current that can be drawn from a saturated Weston Cell without damaging it,is

  • 100MA momentarily
  • 100µA continuously
  • 100 µA momentarily
  • 1 mA momentarily

14. The internal resistance of a saturated Weston Cell is of the order of :

  • A few ohm
  • A few kilo ohm
  • A few hundreds of ohm
  • A fraction of ohm

15. The decrease in the value of emf of an unsaturated Weston Cell is :

  • About 1 µ V per year
  • About 1 mV per year
  • About 5 – 10 µ V per year
  • About 30 – 50 µ V per year

16. Zener sources when used as voltage standards :

  • Are reversed biased
  • Can be designed to cover a wide range of voltages
  • Are immune to the effect of short circuits
  • All of the above.

17. The output voltage Josephon effect standard :

  • Can be changed in a continuous manner
  • Can be changed only in a discrete steps
  • Can be changed continuously as well as in discrete steps
  • Can not be changed

18. Candela can be defined as the luminous intensity in the perpendicular, of a surface of :

  • 1/2 59000 square metre of a full radiator
  • 1/600 square centimeter of a full radiator
  • 1/5,89,000 square metre of a full radiator
  • 1/600, 000 square metre of a full radiator

19. The material of wires used for making resistance standard is usually :

  • Manganin
  • Nichrome
  • Copper
  • Phosphor Bronze.

20. In order to reduce skin effect in resistance standards when they are used on high frequency a.c :

  • The diameter of the resistance wire should be small
  • Adjacent turns of the resistance coil should carry currents in the opposite direction
  • They should be provided with four terminals
  • All of the above

 

 

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