Ques.41. In a transmission line, the voltage regulation is negative whenever receiving end voltage Vs

Less than the sending end voltage

Greater than the sending end voltage

Equal to the sending end voltage

Half of the sending end voltage

Answer.2. Greater than the sending end voltage

Explanation:-

Voltage regulation:- When a transmission line is carrying current, there is a voltage drop in the line due to resistance and inductance of the line. The result is that the receiving end voltage (V_{R}) of the line is generally less than the sending end voltage (V_{s}). This voltage drop (V_{s} − V_{R}) in the line is expressed as a percentage of receiving end voltage V_{R} and is called voltage regulation.

The difference in voltage at the receiving end of a transmission line between conditions of no-load and full-load is called voltage regulation and is expressed as a percentage of the receiving end voltage. Mathematically,

Obviously, it is desirable that the voltage regulation of a transmission line should be low i.e., the increase in load current should make very little difference in the receiving end voltage. In the transmission line, the voltage regulation is negative whenever the receiving end voltage V_{R} is Greater than the sending end voltage.

The regulation will depend upon the power factor of the load. If the power factor is lagging, the voltage at the sending end is more than that at the receiving end. Hence, voltage regulation is positive. On the other hand, if the power factor is leading, the voltage at the sending end will be somewhat less than that at the receiving end. In that case, the regulation is negative.

Ques.42.

1 Ω

5 Ω

10 Ω

2 Ω

Answer.3. 10Ω

Explanation:-

From the figure it can be concluded that the voltmeter reads 5 volts as shown in the figure below.

Here

Current I = 1/2 A = 0.5 A

Voltage V = 5 V

R = V/I = 0.5/5

R = 10Ω

Ques.43. What is the reason behind using a centrifugal switch in a single-phase induction motor?

To protect the motor from overloading

To cut-off the starting winding at an appropriate instant

To out in the capacitor during running conditions

To improve the starting performance of the motor

Answer.2. To cut-off the starting winding at an appropriate instant

Explanation:-

The centrifugal switch is used to disconnect the starting winding of the motor once the motor approaches its normal operating speed i.e 50% – 70% speed.

Ques.44. In an AC network, the load connected is (10 + j10). The phase relation between the voltage applied and the current through the load is:

Voltage and current are in phase with each other

Voltage lags current by 30°

Voltage leads current by 45°

Voltage lags current by 45°

Answer.3. Voltage leads current by 45°

Explanation:-

L0ad impedance Z = R + jX

z = 10 + 10j

Phase angle θ= tan^{−1}(I_{L}/I_{R})

θ= tan^{−1}(10/10)

tanθ = 1

tanθ =45°

Ques.45. Which of the following plants experiences chain reactions?

Thermal power plant

Nuclear power plant

Gas power plant

Hydro-electric power plant

Answer.2. Nuclear power plant

Explanation:-

A nuclear power plant is a steam turbine plant where steam is generated by a nuclear reactor. Nuclear energy is the energy that is trapped inside each atom. Nuclear energy is obtained by fission of uranium-plutonium or thorium or the fusion of hydrogen into helium.

In normal conditions, the energy released due to the disintegration of a uranium atom is significantly low. The capturing of neutrons by the uranium-235 is rather easy and to fission it for the release of the energy. In a chain reaction, particles released by the splitting of the atom strike other uranium atoms and split them. The particles released by this further split other atoms in a chain process. The chain reaction gives off heat energy. This heat energy is used to boil heavy water at the core of the reactor.

Ques.46. _______ is the measuring unit of inductive susceptance.

Tesla

Mho

Weber

Henry

Answer.2. MHO

Explanation:-

Susceptance is symbolized by the capital letter B. It is the reciprocal of AC reactance. Susceptance, like reactance, can be either capacitive or inductive. In the case of a magnetic field, the susceptance is inductive. In the case of an electric field, the susceptance is capacitive. Capacitive susceptance is symbolized B_{C} and inductive susceptance is symbolized B_{L}. In the case of a magnetic field, the susceptance is inductive. In the case of an electric field, the susceptance is capacitive. Inductive susceptance is assigned negative imaginary number values, and capacitive susceptance is assigned positive imaginary number values.

The formula for inductive susceptance is

B_{L} =–1/2πfL

The unit of Inductive susceptance is Siemen or Mho.

Ques.47. The trade name of the Nickel-Copper alloy, that is used as a heating element is:

Eureka

Kanthal

Nichrome

Steel

Answer.1. Eureka

Explanation:-

Constantin‘, also known as ‘Eureka wire‘, is the trade-name for a copper-nickel alloy (approx. 60:40 ratio) formulated in the late 1800s by Edward Weston.

Ques.48. Extension of moving iron ammeter range can be done by using

Inductor

Capacitor

Multiplier

Shunt

Answer.4. Shunt

Explanation:-

Extending the range of a moving coil meter

A moving coil meter is a current-operated instrument with a linear scale. In other words, the deflection of the pointer from zero is in proportion to the current. If the current through a moving coil meter is increased, the deflection of the pointer increases. If the current exceeds the maximum reading on the scale, referred to as the ‘full-scale’ deflection, the coil of the instrument could be permanently damaged due to the heating effect of the current.

Extending the range of an ammeter

The range of an ammeter can be extended by connecting a shunt (a resistance of low value) in parallel with the ammeter. The value of the resistance to be connected in parallel will depend upon the extent to which the range of the ammeter is to be increased. The manufactures generally make moving coil meters of range 0 to 10 mA. They connect resistance of suitable values with the ammeter to extend the range as per the requirement. Since shunt is small resistance. Therefore the resistance of the ammeter is very small.

The full-scale current for a sensitive meter may be of the order of a milliampere or less. For this reason, a ‘shunt’ resistor, in parallel with the meter, is used to extend the current range of the meter.

Extending the range of a voltmeter

The p.d. across a moving coil, the meter is proportional to the current. A voltmeter is used to measure the potential difference across a resistor. A voltmeter is always connected in parallel across a resistor.

The meter may be used to measure p.d. provided the current does not exceed the full-scale current. However, since the resistance of most moving coil meters is low, the full-scale current is reached when the p.d. is no more than of the order of millivolts. To extend the range of a moving coil voltmeter, a ‘multiplier’ resistance is connected in series with the meter.

Let the full-scale voltage across the meter = v and the resistance of the meter = r. Hence the maximum current through the meter, I= v r. This is also the maximum current through the multiplier since the multiplier is in series with the meter. To read voltages up to V, the excess voltage (V — v) must be dropped across the multiplier.

Ques.49. Which of the following should be used under no-load conditions?

Isolator

Rewireable fuse

Air-break switch

Circuit breaker

Answer.1. Isolator

Explanation:-

Isolator or disconnecting Switch: An isolator is a switch that is designed to open a circuit under no-load condition. Its main purpose is to isolate one portion of the circuit from the other and is not allowed to be opened while current is flowing in the line. Such switches are used on both sides of a circuit breaker so that its repair works or replacement could be done.

Note that an isolator is never opened until the circuit breaker in the circuit is opened and it is closed before the circuit breaker is closed. If an isolator is switched OFF when a high current is flowing through the circuit, a heavy spark will be produced. This heavy spark may break the supporting insulator of the isolator which may cause a fatal accident to the operator.

Ques.50. Which motor is referred to as a universal motor?

Series

Shunt

Single-phase induction

Synchronous

Answer.1. Series

Explanation:-

Universal motors may be powered by either AC or DC power sources.

The universal motor is constructed in the same way as a series-wound DC motor. However, it is designed to operate with either AC or DC applied.

The series-wound motor is the only type of DC motor that will operate with AC applied.

The windings of shunt-wound motors have inductance values that are too high to allow the motor to function with AC applied.

The series-wound motors have windings that have low inductances (few turns of large diameter wire), and they, therefore, offer a low impedance to the flow of AC.

The universal motor is one type of AC motor that has concentrated or salient field windings. These field windings are similar to those of all DC motors.