Electrical and Electronic Measurement
Exam Duration: 45 Mins Total Questions : 30
The full scale deflection current of an ammeter is 1mA and its internal resistance is 100Ω.This meter is to deflection when 100Ω is measured.What is the value of series resistor to be used?
- (a)
99.90kΩ
- (b)
100kΩ
- (c)
99.99Ω
- (d)
100Ω
Two ammeters, one with full scale current of 1mA and internal resistance of 100Ω and an other a full scale current of 10 mA and internal resistance of 25Ω are in parallel.What is the total current, these two meters can carry without any meter reading out of scale?
- (a)
1mA
- (b)
10mA
- (c)
11mA
- (d)
5mA
For a given frequency, the deflecting torque of an induction ammeter is directly proportional to
- (a)
(current)2
- (b)
(current)3
- (c)
\(\sqrt{current}\)
- (d)
current
A slide wire potentiometer has 10 wires of 2 m each.With the help of a standard voltage source of 1.045 V, it is standardized by keeping the jockey at 104.5 cm. If the resistance of potentiometer wires is 2000Ω, then the value of working current is
- (a)
1 mA
- (b)
10 mA
- (c)
0.1 mA
- (d)
0.5 mA
Match List I with List II and select the correct answer using the codes given below the lists.
List I | List II |
---|---|
P. Schering's bridge | l . Insulation resistance |
Q. Anderson's bridge | 2. Self inductance |
R. Megger | 3. Capacitance |
S. Campbell's bridge | 4. Mutual inductance |
- (a)
P Q R S 3 2 1 4 - (b)
P Q R S 2 3 1 4 - (c)
P Q R S 3 1 4 2 - (d)
P Q R S 1 2 4 3
In Maxwell's capacitance bridge for calculating unknown inductance, the various values at balance are- R2 =300Ω, R3 =700Ω, R3 =1500Ω, C4 =0.8 μF Calculate R1' L1 and Q factor, if frequency is 1100 Hz.
- (a)
240Ω, 0.12 H, 3.14
- (b)
140Ω, 0.168 H, 8.29
- (c)
140Ω,0.12 H, 5.92
- (d)
240Ω,0.36 H, 8.29
Calculate the power factor of a load, if the meter constant of meter making 1500 revolutions is 350 rev/kW-h, when operating at 230 V and 5 A for 7 h.
- (a)
0.6
- (b)
0.5
- (c)
0.8
- (d)
0.532
When testing a coi I having a resistance of 10 Ω, resonance occurred when the oscillator frequency was 10 MHz and the rotating capacitor was set at 500/2\(\pi\) pF. The effective value of the Q of the coil is
- (a)
200
- (b)
254
- (c)
314
- (d)
542
Choose the correct statement regarding two wattmeter method for power measurements in 3-phase circuit.
- (a)
When power factor is unity, one of the wattmeter reads zero
- (b)
When the readingsof the two wattmeters are equal but opposite sign, the power factor is zero
- (c)
Power can be measured using two wattmeter method only for star connected 3-phase circuit
- (d)
When two wattmeters show identical readings, the power factor is 0.5
The line to line input voltage to the 3-phase, 50 Hz, AC circuit shown in figure is 100 V rms. Assuming that the phase sequence is RYB, the wattmeters would read
- (a)
W1 =886 Wand W2 =886 W
- (b)
W1 =500 Wand W2 =500 W
- (c)
W1 =0 and W2 =1000 W
- (d)
W1 =250WandW2 =750W
A manganin swamp resistance is connected in series with a moving coil ammeter consisting of a milli-ammeter and a suitable shunt in order to
- (a)
minimize the effect of temperature variation
- (b)
obtain large deflecting torque
- (c)
reduce the size of the meter
- (d)
minimize the effect of stray magnetic fields
The effect of stray magnetic fields on the actuating torque of a portable instrument is maximum when the operating field of the instrument and the stray fields are
- (a)
perpendicular
- (b)
parallel
- (c)
inclined at 60°
- (d)
inclined at 30°
The time/div and voltage/div axes of an oscilloscope have been erased. A student connects a 1 kHz,S V p-p square wave calibration pulse to channel 1 of the scope and observes the screen to be as shown in the upper trace of the figure. An unknown signal is connected to channel 2 (lower trace) of the scope.If the time/div and Voltage/div on both channels are the same, the amplitude (p-p) and period of the unknown signal are respectively
- (a)
5 V and 1 ms
- (b)
5 V and 2 ms
- (c)
7.5 V and 2 ms
- (d)
10 V and 1 ms
The bridge shown in the below figure is
- (a)
Maxwell's bridge
- (b)
Wien's bridge
- (c)
Anderson's bridge
- (d)
Hay's bridge
Match the list I with List II and select the correct answer using the codes given below the lists.
List I | List II |
---|---|
P.Wien's bridge | 1.Measurement of resistance` |
Q.Maxwell's bridge | 2.High q inductors |
R.schering's bridge | 3.Measurement of frequency |
S.Anderson's bridge | 4.High voltage capacitors |
T.Blumbeim's bridge | 5.Low Q inductors |
6.Insensitive to stray electrostatic fields |
- (a)
P Q R S T 3 5 4 3 6 - (b)
P Q R S T 5 4 4 6 1 - (c)
P Q R S T 6 4 5 6 3 - (d)
P Q R S T 4 5 3 6 1
A DC potentiometer is designed to measure up to about 2 V with a slide wire of 300 mm. A standard cell of emf 1.18 V obtains balance at 600 mm. A test cell is seen to obtain balance at 680 mm. The emf of the test cell is
- (a)
1.00V
- (b)
1.34V
- (c)
1.50V
- (d)
1.70V
The source of emission of electrons in a CRT is
- (a)
p-n junction diode
- (b)
a barium and strontium oxide coated cathode
- (c)
accelerating anodes
- (d)
post-accelerating anodes
A recorder
- (a)
is an indicating instrument which displays a time varying signal
- (b)
is a device whose function is to record the value of quantity as it is being measured
- (c)
records electrical and non-electrical quantities as a function of time or relates two signals to each other
- (d)
Both (b) and (c)
The voltage-flux adjustment of a certain single-phase 220 V induction watt-hour meter is altered so that the phase angle between the applied voltage and the flux due to it, is 85° (instead of 90°).The errors introduced in the reading of this meter when the current is 5 A at power factors of unity and 0.5 lagging are respectively
- (a)
3.8 mW and 77.4 mW
- (b)
- 3.8 mW and - 77.4 mW
- (c)
- 4.2 Wand - 85.1 W
- (d)
4.2 Wand 85.1 W
The inductance of a certain moving-iron ammeter is expressed as \(L=10+3\theta-{\theta^2\over 4}\mu H,\) where θ is the deflection in radian from the zero position.The control spring torque is 25 x 10-6 Nm/rad. The deflection of the pointer in radian when the meter carries a current of 5 A, is
- (a)
2.4
- (b)
2.0
- (c)
1.2
- (d)
1.0
A 2001/ Current Transformer (CT) is wound with 200 turns on the secondary on a toroidal core. When it carries a current of 160 A on the primary, the ratio and phase errors of the CT are found to be -0.5% and 30 min respectively. If the number of secondary turns is reduced by t, the new ratio error (in %) and phase error (in min) will be respectively
- (a)
0.0 and 30
- (b)
- 0.5 and 35
- (c)
-1.0 and 30
- (d)
-1.0 and 25
A CRO probe has an impedance of 500 kΩ in parallel with a capacitance of 10 pF. The probe is used to measure the voltage between P and Q as shown in figure. The measured voltage will be
- (a)
3.53V
- (b)
4.37V
- (c)
4.54V
- (d)
5.00
A DC ammeter has a resistance of 0.1 0 and its current range is 0-100 A. If the range is to be extended to 0-500 A, the meter requires which of the following shunt resistance?
- (a)
0.010Ω
- (b)
0.011Ω
- (c)
0.025Ω
- (d)
1.0Ω
A 1000 V DC supply has two l-core cables as its positive and negative leads; their insulation resistances to earth are 4 MΩ and 6 MΩ respectively, as shown in figure. A voltmeter with resistance 50 kΩ is used to measure the insulation of the cable.When connected between the positive core and earth, the voltmeter reads
- (a)
8V
- (b)
16V
- (c)
24V
- (d)
40V
Two wattmeters, which are connected to measure the total power on a three-phase system supplying a balanced load, read 10.5 kW and - 2.5 kW respectively. The total power and the power factor respectively are
- (a)
13.0 kW and 0.334
- (b)
13.0 kW and 0.684
- (c)
8.0 kW and 0.52
- (d)
8.0 kW and 0.334
An average-reading digital multimeter reads 10 V when fed with a triangular wave, symmetric about the time-axis. For the same input an rms reading meter wi II read
- (a)
\(20/\sqrt3\)
- (b)
\(-10/\sqrt3\)
- (c)
\(-20/\sqrt3\)
- (d)
\(10/\sqrt3\)
A circuit tuned to a frequency of 1.5 MHz and having an effective capacitance of 150 pF. In this circuit, the current falls to 70.7% of its resonant value when the frequency of an emf of constant magnitude injected in series with the circuit deviates from the resonant frequency by 5 kHz.Q factor is
- (a)
50
- (b)
100
- (c)
150
- (d)
200
A circuit tuned to a frequency of 1.5 MHz and having an effective capacitance of 150 pF. In this circuit, the current falls to 70.7% of its resonant value when the frequency of an emf of constant magnitude injected in series with the circuit deviates from the resonant frequency by 5 kHz.Effective resistance of circuit is
- (a)
2Ω
- (b)
3Ω
- (c)
5.5Ω
- (d)
4.7Ω
A resistance R is measured using the connection shown in below figure.
The current measured is 10 A on range 100 A and the voltage measured is 125 V on 150 V range. The scales of the ammeter and voltmeter are uniform. The total number of scale divisions of ammeter is 100 and of volt meter is 150. The scale division can be distinguished. The constructional error of the ammeter is ± 0.3% and that of voltmeter ± 0.4%. The resistance of the ammeter is 0.25Ω.The value of R is
- (a)
12.5
- (b)
12.25
- (c)
12.75
- (d)
12.0
A resistance R is measured using the connection shown in below figure.
The current measured is 10 A on range 100 A and the voltage measured is 125 V on 150 V range. The scales of the ammeter and voltmeter are uniform. The total number of scale divisions of ammeter is 100 and of volt meter is 150. The scale division can be distinguished. The constructional error of the ammeter is ± 0.3% and that of voltmeter ± 0.4%. The resistance of the ammeter is 0.25Ω.Possible error in results of part A is
- (a)
±0.11Ω
- (b)
±0.15nΩ
- (c)
± 0.867Ω
- (d)
± 0.625Ω