Ques 41. The AC bridge used for measurement of dielectric loss of capacitor is
Anderson Bridge
Schering bridge✔
Wien bridge
Hay’s bridge
Schering bridge is used to measure the capacitance of the capacitor, dissipation factor and measurement of relative permittivity.
Ques 42. In an electrodynamometer ammeter, the deflection of the pointer is proportional to
Mean of currents in fixed coil a moving coil
Square of the current in moving coil
RMS value of current in fixed coil
Mean-square of currents in fixed coil and moving coil✔
In Electrodynamometer for d.c, the deflection is proportional to the square of the current For a.c the instantaneous torque is proportional to the square of the instantaneous current. The i2 is positive and as the current varies, the deflecting torque also varies.
Due to inertia, the moving system cannot follow rapid variations and thus final meter shows the average torque.
Thus the deflection is the function of the mean of the squared current. Therefore the scale is calibrated in terms of the square root of the average current squared ie. R.M.S. value of the A.C Quantity to be measured.
Ques 43. In which of the following transformers, is the secondary winding always kept closed
Current transformer✔
Potential transformer
Power transformer
Distribution transformer
If current transformer secondary is not shorted when unused and kept open then it can develop a very high voltage across secondary which may damage transformer insulation.
Ques 44. Two holes are drilled in the disc on a diameter of an energy-meter to
Increase ventilation
Reduce the weight of disc
Eliminate creeping on no-load✔
Increase deflection torque
The slow but continuous rotation of the disc when only the pressure coils are excited but no current is flowing in the circuit is called “creeping”.
To overcome this creeping effect on no-load, two holes are drilled in the disc on a diameter, i.e. on opposite sides of the spindle. This causes sufficient distortion of the field to prevent rotation when one of the holes comes under one of the poles of the shunt magnet.
Ques 45. Which of the following instruments has the highest torque/weight ratio among the given instruments?
Attraction type MI instrument
Repulsion type MI instrument
Permanent magnet moving coil instrument✔
Electrodynamometer instrument
The torque/weight ratio indicates Sensitivity. If a pointer is having less weight, it will be having high torque/weight ratio so that even for a very small deflection pointer starts moving and indicates the measured value.
The permanent magnet moving coil instrument (PMMC) has the highest torque/weight ratio.
Ques 46. If current through the operating coil of a moving iron instrument is doubled, the operation force becomes
One and a half times
2 times
3 times
4 times✔
The moving iron instruments are of two types
Attraction type
Repulsion type
The deflecting torque in both the instrument is proportional to the square of the current i.e
Deflecting torque ∝ ( current)2
Hence if the current is doubled the deflecting torque or operating force becomes four times.
Ques 47. In moving iron instruments, the iron moves in a direction to cause
Coil inductance to be constant
Mutual inductance to be minimum
Minimum reluctance path✔
Decrease in the flux passing through is
In the moving iron instruments, vane is made up of soft iron and high permeability steel because it can move in the magnetic field of the stationary coil carrying the current hence the iron vane always try to adjust along the minimum reluctance path.
Ques 48. A moving coil instrument has a resistance of 10Ω and gives full-scale deflection at a 0.5 V potential difference across it. How can it be adapted to measure a current upto 100 A?
By connecting shunt resistance of 0.005 Ω across the meter✔
By connecting shunt resistance of 0.05 Ω across the meter
By connecting shunt resistance of 5 Ω across the meter
By connecting shunt resistance of 10Ω across the meter
Let shunt resistor R is connected in parallel
V = IR
Req = R × 10/R + 10
0.5 = 100(R × 10)/ R + 10)
0.5R + 5 = 1000R
= 0.005Ω
Ques 49. The multiplying power of the shunt of a milliammeter is 8. If the circuit is 200 mA, then-current through the meter is
25 mA✔
200 mA
1600 mA
3200 mA
Multiplying power of the shunt is given as
Multiplying power = I/Im
Where I = current of the circuit to be measured
Im = Current passing through the ammeter
8 = 200/Im
Im = 200/8 = 25mA
Ques 50. The material to be used in the manufacture of a standard resistor should be of
Low resistivity
High resistivity and low-temperature coefficient✔
High-temperature coefficient
Low resistivity and high-temperature coefficient
The material to be used in the manufacture a standard resistor should have high resistivity and very low dependence on temperature because it is desired that resistance should remain constant and it should be independent of the temperature.
