InterviewSolution
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InterviewSolution
This section includes InterviewSolutions, each offering curated multiple-choice questions to sharpen your knowledge and support exam preparation. Choose a topic below to get started.
| 101. |
Insertion of a dielectric material between the plates of an air capacitor |
| Answer» . | |
| 102. |
Two ammeters A and B are connected in parallel in a circuit carrying 100 A. Their resistances are 0.8 mΩ. Their readings will be. |
| Answer» . | |
| 103. |
In figure, Z = 100∠50°, Z = 300∠-90° and Z = 200∠0°. For balanced condition, Z will be |
| Answer» . | |
| 104. |
In household energy meters the flux of series magnet is in phase with current but the flux of shunt magnet lags the voltage by 88°. The reading of energy meters |
| Answer» Since angle is less than 90°, reading will be less. Therefore error is negative and correction is positive. | |
| 105. |
The emf of a Weston cell is 1.286 V. |
| Answer» It is 1.01859. | |
| 106. |
The power factor of a single phase load can be calculated if instruments available are |
| Answer» , we need to, measure active power, voltage and current. | |
| 107. |
A sinusoidal signal is measured by CRO. The scale is set at 4 mV/cm. If vertical distance between positive and negative peaks is 6 cm, the peak value of ac signal is |
| Answer» , Peak to peak value will be 24 mV. | |
| 108. |
Wheatstone bridge is suitable for low resistances. |
| Answer» It is suitable for medium resistances. | |
| 109. |
To avoid creep in an energy meter |
| Answer» When a hole comes under a pole of upper electromagnet the disc becomes stationary. Thus creep is avoided. | |
| 110. |
A wire strain gauge has a gauge factor of 2, resistance of 125 Ω and length 1 m. If length of wire changes by .005 m, change in resistance will be |
| Answer» . | |
| 111. |
The deflection of a DArsonval galvanometer is measured through a mirror and scale. The mirror is 1 m away from the light source. The mirror is mounted on, the moving system. If mirror rotates through 0.2 rad the displacement on the scale is |
| Answer» Diplacement = (1) (2θ) = 0.4 m. | |
| 112. |
Two ammeters having resistances of 0.5 Ω and 0.25 Ω and having full scale reading of 25 A each are connected in parallel. To ensure that neither of them goes beyond scale, the total current should not be more than |
| Answer» or V = 37.5 V. | |
| 113. |
An amplifier has to amplify pulses of 1 H-s duration. The minimum bandwidth of amplifier must be |
| Answer» Time period of 1 μs corresponds to frequency of 1 MHz. | |
| 114. |
A moving coil meter has a resistance of 50 ohms and a full scale deflection current of 20 mA. To convert it into a voltmeter of 0-100 V range, the series resistance should be |
| Answer» . | |
| 115. |
In measuring a resistance by voltmeter-ammeter method, the voltmeter can be connected either across supply or across the resistance. If the resistance is low, the voltmeters should be connected |
| Answer» Since resistance is low current is high and voltage drop across ammeter is high. Therefore, voltmeter should be connected across resistance. | |
| 116. |
For measurement of surface temperature of solids the elements of RTD is usually in the shape of |
| Answer» The flat grid is attached to the surface of solid. | |
| 117. |
Two resistances R = 18.7 Ω. and R = 3.624 Ω in series. The total resistance to the appropriate number of significant figures is |
| Answer» Since second and third decimal places of R1 are not known, we can take only first decimal place of R2. | |
| 118. |
The input impedance of CRO is about |
| Answer» CRO has very high input impedance. | |
| 119. |
The wave applied to X plates, for ohtaining trace of voltage wave, is |
| Answer» It is called time base signal. | |
| 120. |
The response of a thermistor overs the whole of its temperatures range is |
| Answer» It is a non-linear device. The change of resistance with temperature is non-linear. | |
| 121. |
A polyphase wattmeter basically consists of two wattmeters. The moving system of two wattmeters |
| Answer» The moving system has to be common since reading depends on the action of both wattmeters. | |
| 122. |
The dead zone in a pyrometer is 0.125% of span. The calibration is 400°C to 1000°C. What temperature change might occur before it is detected. |
| Answer» Span = 600°, . | |
| 123. |
The dimensions of force are |
| Answer» F = ma = MLT-2. | |
| 124. |
For use at 50 Hz the range of scale of vibrating reed frequency meter is |
| Answer» Generally the frequency does not fall below 47 Hz and does not exceed 53 Hz. | |
| 125. |
A variable reluctance type tachometer has 150 teeth on rotor. The counter records 13500 pulse/sec. The rotational speed is |
| Answer» . | |
| 126. |
The current through the coil of an electromagnet is doubled. The magnetic field around the coil |
| Answer» B ∝ H. | |
| 127. |
In a moving iron voltmeter the coil has a resistance of 20 Ω and an inductance of 0.3 H. The swamping resistance in 2000 Ω. To ensure correct reading with dc as well as 50 Hz ac, the value of capacitor to be connected in parallel with swamping resistance should be |
| Answer» C = 0.41 L/R2 or C = (0.41 x 0.3)/(2000)2 = 0.0311 x 10-6 F. | |
| 128. |
If a shunt of 200 Ω resistance is used with a galvanometer of 1000 Ω resistance, the multiplying power is |
| Answer» If current through galvanometer is 1, A current through shunt = . Total current = 6 I. Hence multiplying factor is 6. | |
| 129. |
In a thermocouple two metal junctions between metals and are kept at temperature and . The thermocouple emf is produced because |
| Answer» The two materials in thermocouple are different and the two junctions are kept at different temperatures. | |
| 130. |
The scale of dynamometer wattmeter is non linear. |
| Answer» It is linear. | |
| 131. |
Magnetic deflection is inversely proportional to |
| Answer» where VA is the potential difference between anode and cathode. | |
| 132. |
To increase Q factor of a coil, the wire should be |
| Answer» Q is high if resistance is low. Therefore, wire should be thick. | |
| 133. |
An ammeter of 0-25 A range has a guaranteed accuracy of 1% of full scale reading. The current measured is 5 A. The limiting error is |
| Answer» . | |
| 134. |
The coil of a moving iron instrument has a resistance of 500 Ω and an inductance of 1 H. It reads 250 V when a 250 V dc is applied. If series resistance is 2000 Ω, its reading when fed by 250 V, 50 Hz ac will be |
| Answer» | |
| 135. |
In 3 phase power measurement by two wattmeter method, the reading of one wattmeter is zero. The power factor of load is |
| Answer» When p.f. = 0.5, 0 = 60° and one of the wattmeters reads zero. | |
| 136. |
A dynamometer wattmeter is connected in ac circuit. The measured power is |
| Answer» All wattmeters measure average power over a cycle. | |
| 137. |
Loss of charge method is suitable for medium resistances. |
| Answer» It is suitable for high resistances. | |
| 138. |
In two wattmeter method of 3 phase power measurement, when does one wattmeter read negative |
| Answer» When p.f. is less than 0.5 (leading or lagging) one of the wattmeters reads negative. | |
| 139. |
In figure, Z = 200∠60° Ω, Z = 400∠ - 90° Ω, Z = 300∠0°. Then Z for bridge to be balanced is |
| Answer» . | |
| 140. |
In a ballistic galvanometer, a charge of 100 μC gives a first swing of 25°. The charge required to cause first swing of 50° is |
| Answer» swing is proportional to charge. | |
| 141. |
Two resistors = 36 Ω ± 5% and = 75 Ω ± 5% are connected in series. The total resistance is |
| Answer» Total maximum error ± (1.8 + 3.75) = ± 5.55 Ω. | |
| 142. |
Figure shows an RC potentiometer to measure ac voltage. It is desired that V/V should be independent of frequency. The value of C should be |
| Answer» Since resistances are in the ratio of 10 : 1, capacitances should be in the ratio of 1 : 10 because XC ∝ 1/C. | |
| 143. |
In a strain measuring device using a strain gauge, the output quantity is |
| Answer» The measurement is done using an unbalanced bridge. | |
| 144. |
If reference sound pressure P is 2 x 10 N/m, a sound pressure of 90 dB is equal to |
| Answer» . | |
| 145. |
A single phase energy meter has the rating 1200 resolutions/ kWh. If a 500 W electric gadget is used for 4 hours, the energy meter will make |
| Answer» 0.5 x 4 = 2 kWh = 2 x 1200 revolutions. | |
| 146. |
A moving coil instrument has a resistance of 0.6 Ω and full scale deflection at 0.1 A. To convert it into an ammeter of 0-15 A range, the resistance of shunt should be |
| Answer» . | |
| 147. |
A piezoelectric force transducer has a charge sensitivity of 20 pC/N. It is connected to a charge amplifier and overall gain of transducer and amplifier is 50 mV/N. The gain of amplifier is |
| Answer» . | |
| 148. |
An LVDT is used to measure displacement. The LVDT feeds a Voltmeter of 0-5 V range through a 250 gain amplifier. For a displacement 0.5 mm the output of LVDT is 2 mV. The sensitivity of instrument is |
| Answer» Final output = 2 x 10-3 x 250 = 0.5 V. . | |
| 149. |
As per BIS there are 6 accuracy classes of instruments. |
| Answer» There are 8 classes of accuracy as per BIS. | |
| 150. |
Magnetic flux density has the dimensions |
| Answer» Flux density = flux/area. | |