## electrical

### Electrical Instruments MCQ Objective Questions and Answers Page - 2

1.
 High value pot resistance leads to A Low sensitivity B High sensitivity C Low nonlinearity D Less error Answer : B Explanation :
2.
 Which one of the following statements for a potentiometric transducer is correct  ? A It is a zero order displacement transducer. B It is a first order displacement transducer. C It is a zero order temperature transducer. D It is a second order displacement transducer. Answer : A Explanation :
3.
 How can resolution of a wire wound potentiometer be improved  ? A By increasing the applied voltage B By decreasing the applied voltage C By reducing the diameter of the resistance wire D By increasing the diameter of the resistance wire Answer : C Explanation :
4.
 What is the number of turns of wire needed to provide a potentiometer with a resolution of  0.05 per cent  ? A 200 turns B 2000 turns C 20 turns D 20000 turns Answer : B Explanation :
5.
 A 3-turn 100 kΩ potentiometer with  1%  linearity uses  30 V supply. What is the potentiometer constant  ? A 0.1 V/turn B 10 V/turn C 33.33 V/turn D 0.3 V/turn Answer : A Explanation :
6.
 A stain gauge is passive transducer and is employed for converting A Mechanical displacement into a change of resistance B Pressure into a change of resistance C Force into displacement D None of the above Answer : A Explanation :
7.
 The sensitivity factor of strain gauge is normally of the order of A 1 to 1.5 B 1.5 to 2.0 C 0.5 to 1 D 5 to 10 Answer : B Explanation :
8.
 The resistance of  125 Ω strain gauge changes by  1 Ω for  4000 micro-strain. The gauge factor for strain gauge is A 1.5 B 2.0 C 2.5 D 3.0 Answer : B Explanation :
9.
 In wire wound strain gauges, the change in resistance under strained condition is mainly on account of A Change in diameter of wire B Change in length of wire C Change in both length and diameter of wire D Change in resistivity Answer : C Explanation :
10.
 Unbonded strain gauges are A Exclusively used for transducer applications B Exclusively used for stress analysis C Commonly used for both stress analysis and transducer applications D None of the above Answer : B Explanation :
11.
 Bonded strain gauges are A Exclusively used for construction of transducers B Exclusively used for stress analysis C Used for both stress analysis and for construction of transducers D None of the above Answer : C Explanation :
12.
 Over wire strain gauges foil strain gauges have the advantages of A Higher heat dissipation capacity and better bonding B Superior mechanical stability under prolonged stained and high temperature conditions, low hysteresis and creeping effects C Excellent reproducibility and longer life D All of the above Answer : D Explanation :
13.
 In a semiconductor strain gauge, the change in resistance on application of strain is mainly due to change in A Length of the wire B Diameter of the wire C Resistivity of the material of the wire D Both the length and diameter of the wire Answer : C Explanation :
14.
 Which of the following is not an advantage of semiconductor gauges as compared to conventional strain gauges. A Excellent hysteresis characteristics. B Least sensitive to temperature changes C High fatigue life D Smaller size Answer : B Explanation :
15.
 In semiconductor strain gauges, what happens when a tensile strain is applied  ? A Resistance increases in  N-type of materials B Resistance increases in  P-type of materials C Resistance increases in  both  P  and  N-type of materials D Resistance decreases in  both  P  and  N-type of materials Answer : B Explanation :
16.
 The drawbacks of strain gauges are A Low fatigue life B That they are expensive, brittle, highly sensitive to temperature variations C Poor linearity D Both (b) and (c) Answer : D Explanation :
17.
 Strain gauges are constructed with Germanium chips because Germanium A Has a strong Hall Effect B Is crystalline in nature C Can be doped D Has piezoelectric property Answer : C Explanation :
18.
 In a semiconductor strain gauge, the change in resistance on application of strain is A Much higher than the case of metal strain gauges and this is mainly due to change in dimensions B Much higher than the case of metal strain gauges and this is mainly due to change in resistivity C Lower than the case of metal strain gauges D None of the above Answer : A Explanation :
19.
 Measurement of pressure can be done by using wire, foil or semiconductor type strain gauges. The disadvantage of the semiconductor type of strain gauge compared to the other two is in terms of A Gauge factor B Hysteresis characteristics C Temperature sensitivity D Frequency response Answer : C Explanation :
20.
 The wire material of strain gauges should have A High resistivity and high thermo-emfs. B Low resistivity and high thermo-emfs. C Low resistivity and low thermo-emfs. D High resistivity and low thermo-emfs. Answer : D Explanation :
21.
 The carrier material employed with strain gauges at room temperature is A Impregnated paper B Bakelite C Epoxy D Aluminium foil Answer : A Explanation :
22.
 A rosette gauge is used to determine A Principal stress direction only B Principal strain direction only C Principal stress and strain direction and magnitude D Principal strain direction and magnitude Answer : C Explanation :
23.
 Rosette gauges are employed for measuring A Strain in a direction B Variable strain C Strain in more than one direction D Small strains Answer : C Explanation :
24.
 Platinum is the commonly used metal for resistance-temperature detectors (RTDs) because A It is commercially available in pure form at reasonable rates. B It is relatively stable under various environment conditions C It has wide operating temperature range D All of the above Answer : D Explanation :
25.
 Resistance thermometer elements made from semiconductor compounds are called A Hot wire anemometer B Semiconductor temperature sensors C Thermistors D Hot wire resistance transducer Answer : C Explanation :
26.
 Semiconductor thermometers have the disadvantage that these A Are not readily available and are expensive B Are fragile and have low sensitivity C Are large in size and have a poor frequency response D None of the above Answer : B Explanation :
27.
 A semiconductor device made out of a material having very high temperature coefficient of resistance is A Transistor B Varistor C Thyristor D Thermistor Answer : D Explanation :
28.
 The temperature coefficient of resistance for a thermistor is A Low and negative B Low and positive C High and negative D High and positive Answer : C Explanation :
29.
 For which one of the following measurements a thermistor can be used  ? A Velocity B Humidity C Displacement D Percent of  CO2  in air Answer : D Explanation :
30.
 Which one of the following is the most sensitive device  ? A Thermocouple B RTD C Thermistor D Pyrometer Answer : C Explanation :
31.
 Which of the following should be incorporated in the  RTD  to make a temperature sensing bridge most sensitive to temperature  ? A Platinum B Nickel C Thermistor D Copper Answer : C Explanation :
32.
 A fixed resistor of suitable value is usually connected across a thermistor to A Decrease its resistance B Increase its sensitivity C Compensate its self-heating effect D Improve linearity Answer : D Explanation :
33.
 Three phenomena which govern the behaviour of a thermocouple are A Thomson effect, Seebeck effect, anisotropic effect. B Hall effect, Seebeck effect, Peltier effect. C Peltier effect, Thomson effect, anisotropic effect. D Seebeck effect, Peltier effect, Thomson effect. Answer : D Explanation :
34.
 Cold junction in a thermocouple is A The reference junction maintained at a known constant temperature B The junction maintained at a very low temperature C The Junction at which the temperature is sensed D None of the above Answer : A Explanation :
35.
 Thermocouples A Are most commonly employed for indication of rapidly changing temperature and for use in localized and in otherwise accessible positions B Need reference junction compensation C Have a low output voltage level D All of the above Answer : D Explanation :
36.
 The drawbacks of thermocouples are that A They are less accurate that  RTDs  and thermistors B They need compensating leads C Reference junction compensation is required in thermocouples D All of the above Answer : D Explanation :
37.
 For a thermocouple pair  (A, B)  the extension wires  (C, D) A Should be identical pair elements B Should be identical temperature emf relationship C Can be of any two dissimilar materials D Should have very small temperature emf sensitivity Answer : A Explanation :
38.
 Which one of the following thermocouple has the highest temperature measuring range  ? A Copper-Constantan B Iron- Constantan C Alumel-Chromel D Platinum Rhodium-Platinum Answer : C Explanation :
39.
 DC tachometer generators are sometimes preferred over ac tachometer generators because A It is possible to know the direction of rotation B They present no maintenance problems C It is possible to know the direction of rotation and magnitude of speed with the help of simple dc voltmeter D All of the above Answer : C Explanation :