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Multiple choice question for engineering

Set 1

1. Why is the scale of a megger calibrated in megaohms?
a) to indicate resistance
b) to minimise the current flow
c) to increase the voltage drop
d) to reduce the temperature

View Answer

Answer: a [Reason:] Current flow through the circuit depends on the magnitude of the e.m.f source. In order to indicate the resistance value indicated by the pointer, the scale of a megger is calibrated.

2. Megger can be used for verifying the electrical insulation level of
a) passive components such as resistance, capacitor and inductance
b) devices such as motor, cable, etc
c) solid state devices
d) liquid crystal devices

View Answer

Answer: b [Reason:] Solid state devices consist of power electronic components and drives. One of the applications of a Megger circuit is in verifying the electrical insulation levels of devices such as motor, cable, generator, etc.

3. Continuity between any two points can be measured using
a) ammeter
b) voltmeter
c) megger
d) galvanometer

View Answer

Answer: c [Reason:] A galvanometer is used for detecting the balance condition in a bridge circuit. An ammeter measures the current flow through the circuit while the voltmeter is used for determining the voltage across the bridge circuit. A megger circuit can be used to determine the continuity between any two points.

4. Electrical continuity between any two points exists if
a) there is current flow through them
b) there is a wire connecting the points
c) there is sufficient voltage drop
d) pointer shows deflection

View Answer

Answer: d [Reason:] Voltage drop across the circuit is measured by using a voltmeter. When the pointer displays full deflection, then there is an electrical continuity between the two points.

5. Megger is also known as _________
a) megaohmmeter
b) multimeter
c) galvanometer
d) ammeter

View Answer

Answer: a [Reason:] A galvanometer is used to detect the balance condition. A multimeter can be used for measurement of voltage, current, resistance and power. A megger is also known as a megaohmmeter as it is used for the measurement of resistances in the order of Mῼ.

6. The application of a megger is _________
a) to measure resistance
b) to test for leakage
c) to limit the current
d) to increase the emf of the circuit

View Answer

Answer: b [Reason:] Current flow through a circuit depends on the magnitude of the voltage source. Magnitude of the voltage source can be increased. A megger is mainly used for testing electrical leakages in wires.

7. What is the significance of a megger with respect to high resistance?
a) it is used to limit the current
b) it is used to provide stability
c) used for measuring high resistance with respect to ground
d) it is used for temperature protection

View Answer

Answer: c [Reason:] Temperature protection can be provided to a bridge circuit by making use of heat sinks. Megger is used for determining very high resistances between the conducting part of a circuit and ground.

8. How is the megger calibrated?
a) in steps of 1 unit per division
b) based on the value of resistance to be measured
c) directly calibrated on the position of the pointer
d) reversely calibrated based on the pointer position

View Answer

Answer: d [Reason:] The scale in a megger is calibrated such that normal position of a pointer indicates infinity while full scale corresponds to zero resistance.

Set 2

1. Wheatstone bridge is a __________
a) a.c. bridge
b) d.c. bridge
c) high voltage bridge
d) power dissipation bridge

View Answer

Answer: b [Reason:] The Wheatstone bridge is a d.c. bridge that is used for the measurement of medium resistance. Schering bridge is used for measurement of high voltages. AC bridges comprise of Anderson bridge, Maxwell Bridge etc.

2. Wheatstone bridge is used to measure resistance in the range of ________
a) 1Ω to a few megaohms
b) 10kΩ to a few megaohms
c) 100MΩ to a few gegaohms
d) 100Ω to a few teraohms

View Answer

Answer: a [Reason:] Wheatstone bridge is the simplest form of bridge circuit. It is basically used for the measurement of medium resistances in the range of 1Ω to a few megaohms.

3. Wheatstone bridge is used to measure the d.c. resistance of various types of wires for
a) determining their effective resistance
b) computing the power dissipation
c) quality control of wire
d) maintaining a source of constant e.m.f

View Answer

Answer: c [Reason:] Wheatstone bridge is used to measure the d.c. resistance of various types of wires for controlling the quality of the wires. Voltage source maintains a constant e.m.f in the bridge circuit.

4. Telephone companies make use of the Wheatstone bridge for _________
a) measuring the telephone resistance
b) computing the line strength
c) maintaining dialtone
d) locating the cable faults

View Answer

Answer: d [Reason:] Cable faults in telephones can be located by telephone companies by making use of a Wheatstone bridge. Telephonic resistances are determined using suitable techniques. Dialtone is maintained through optical fibre technology.

5. The types of faults in a telephone line are ________
a) line to line or line to ground
b) triple line to line or line to ground
c) open circuit and short circuit
d) symmetrical and unsymmetrical

View Answer

Answer: a [Reason:] In a telephone line, line to line and line to ground faults occur. Symmetrical, unsymmetrical, open circuit, short circuit, triple line to line and line to ground faults occur in power systems.

6. How can a Wheatstone bridge be used for the measurement of physical parameters?
a) in conjunction with a rectifier
b) along with an op amp
c) by connecting it to a thermistor
d) by making use of a transducer

View Answer

Answer: b [Reason:] A Wheatstone bridge can be used for the measurement of physical parameters such as temperature, strain, light, etc by making use of an operational amplifier. Rectifier circuits are used for conversion of ac to dc.

7. By using the variations on a Wheatstone bridge we can
a) measure quantities such as voltage, current and power
b) measure high resistance values
c) measure quantities such as complex power
d) measure quantities such as capacitance, inductance and impedance

View Answer

Answer: d [Reason:] In its simplest form a Whetstone bridge consists of resistive arms. A Wheatstone bridge is used for the measurement of quantities such as capacitance, inductance and impedance by making use of the variations.

8. One of the simplest applications of a Wheatstone bridge is ________
a) voltage measurement
b) current measurement
c) light measurement
d) power measurement

View Answer

Answer: c [Reason:] Wheatstone bridge consists of simple resistances in the ratio arms. One of the simplest applications of a Wheatstone bridge is the measurement of light by making use of a photoresistive device.

9. Thermal compensation can be provided in a Wheatstone bridge by ________
a) using more than one resistive sensor
b) making use of a heat sink
c) using cooling fans
d) immersing the circuit into a liquid

View Answer

Answer: a [Reason:] By making use of more than one resistive sensor within the four arms of a Wheatstone bridge we get a full bridge, half bridge or a quarter bridge setup with automatic balancing effect.

Set 3

1. What is the significance of the balance equation on losses?
a) independent of losses in inductance
b) independent of losses in capacitance
c) independent of losses in resistance
d) independent of losses in the circuit

View Answer

Answer: a [Reason:] The balance equation in a Maxwell inductance capacitance bridge is independent of the losses associated with an inductance. According to the balance equation the unknown inductance is computed as Lx = R2 R3 C1

2. Balance equation is dependent on frequency.
a) True
b) False

View Answer

Answer: b [Reason:] The balance equation in a Maxwell inductance capacitance bridge is independent on the measurement of frequency. The balance equation does not contain frequency terms such as ω and as a result, it is independent of frequency.

3. How can R1 be scaled?
a) by using a scale
b) by using an ohmmeter
c) by calibration
d) by using a galvanometer

View Answer

Answer: c [Reason:] The resistance R1 in a Maxwell inductance capacitance bridge can be scaled through calibration. The value of the Quality factor Q can be read directly through calibration.

4. Scale of resistance can be calibrated.
a) True
b) False

View Answer

Answer: a [Reason:] The resistance R1 in a Maxwell inductance capacitance bridge can be calibrated directly. As a result the value of the unknown inductance can be read directly.

5. Bridge can be used for the measurement of _________
a) high Q values
b) intermediate Q values
c) very low Q values
d) low Q values

View Answer

Answer: d [Reason:] A Maxwell inductance capacitance bridge can be used for the measurement of low Q values only of the order of 1 to 10. This is because at high Q factor values the angular balance condition is not satisfied.

6. The balance condition is _________
a) is easy to obtain
b) is difficult to obtain
c) can’t be obtained
d) exists always

View Answer

Answer: b [Reason:] The balance condition in a Maxwell inductance capacitance bridge is difficult to obtain. This occurs due to an interaction between resistance and reactance components in the bridge circuit.

7. Commercial Maxwell bridges measure
a) inductances in the range of 1 to 1000H
b) capacitances in the range of 10mF to 1F
c) resistances in the range of 0.001 Ω to 1Ω
d) power in the range of 1W to 50MF

View Answer

Answer: a [Reason:] Basically a Maxwell bridge is used for the measurement of inductance in terms of known standard capacitance value. Inductances in the range of 1 to 1000H with an accuracy range of ±2% can be measured.

8. At high Q values, the angular balance condition
a) is satisfied
b) is not satisfied
c) is independent of Q factor
d) is partially affected

View Answer

Answer: b [Reason:] For high Q factor values in a Maxwell inductance capacitance bridge, the angular balance condition is affected. The relation θ1 + θ4 = θ2 + θ3 is not satisfied at high Q factor values. This occurs as θ4 reaches 90°. θ1 must become –90° as per the angular balance condition. But for this the value of R1 should be very high, which is not practically feasible.

Set 4

1. In a capacitance bridge, the arms are _________
a) resistive
b) capacitive
c) inductive
d) mixture of resistance, capacitance and inductance

View Answer

Answer: a [Reason:] The capacitance bridge is mainly used for the measurement of unknown capacitance. The ratio arms in a capacitance bridge are resistive in nature.

2. How is the bridge balanced?
a) using resistance R1
b) using resistance R3
c) through capacitance C3
d) through capacitance Cx

View Answer

Answer: b [Reason:] Bridge balance is obtained by varying the resistance R3. At balance we get the value of the unknown resistance as Rx = R1 R3R2.

3. Impedance Z4 consists of _________
a) resistance Rx
b) capacitance Cx
c) combination of capacitance Cx and resistance Rx
d) consists of a detector

View Answer

Answer: c [Reason:] Ratio arm Z4 consists of the unknown impedance. Impedance Z4 consists of capacitance Cx in series with a leakage resistance Rx.

4. Impedance Z3 consists of_________
a) resistance R3
b) capacitance C3
c) vibration galvanometer
d) capacitance C3 in series with resistance R3

View Answer

Answer: d [Reason:] Impedance usually refers to the combination of resistance and either capacitance or inductance. As we are considering the case of capacitance measurement, impedance Z3 comprises capacitance C3 in series with resistance R3.

5. Unknown capacitance value is obtained by _________
a) comparison with standard
b) using a tuned detector
c) using capacitance of other ratio arms
d) using a vibration galvanometer

View Answer

Answer: a [Reason:] Tuned circuit is used for detecting balance condition. Vibration galvanometer is used for the same purpose. Unknown value of capacitance is obtained by comparing it with a standard value.

6. Unknown resistance is obtained by using the relation
electrical-measurements-questions-answers-capacitance-comparison-bridge-q6

View Answer

Answer: b [Reason:] The value of the unknown resistance is obtained by using the relation Rx = R2 R3R1 at balance condition.

7. Unknown capacitance is found by using the relation
electrical-measurements-questions-answers-capacitance-comparison-bridge-q7

View Answer

Answer: c [Reason:] The value of unknown capacitance is found using the relation Cx = C3 R1R2 at balance condition.

8. Actual balance condition can be obtained by _________
a) varying R1
b) varying R3
c) varying R2
d) varying R1 and R3

View Answer

Answer: d [Reason:] Resistances R1 and R3 are variable, while resistance R2 is fixed. By varying the resistances R1 and R3, we get the actual balance condition.

Set 5

1. Potential transformers are used to measure _________
a) high voltages
b) low voltages
c) high currents
d) low currents

View Answer

Answer: a [Reason:] Potential transformers are also known as P.T. and are used in the measurement of high magnitude of voltages.

2. Potential transformers are used with _________
a) high range voltmeter
b) low range voltmeter
c) intermediate range voltmeter
d) very high range voltmeter

View Answer

Answer: b [Reason:] In general, potential transformers are used with low range voltmeters. They are also used for energizing the potential coils of low range energy meters and wattmeters.

3. Potential transformer is similar in design to a
a) C.T.
b) Step up transformer
c) Power transformer
d) Step down transformer

View Answer

Answer: c [Reason:] In terms of design, the potential transformer resembles a power transformer. Potential transformers have a very low loading capacity of the order of a few volt amperes.

4. The secondary winding of a P.T. is designed for
a) 220 V
b) 2.2 kV
c) 1.1 kV
d) 110 V

View Answer

Answer: d [Reason:] A potential transformer is generally used for the measurement of very high magnitude of voltages in a circuit. But the secondary winding of a P.T. is designed for a capacity of 110 V.

5. The primary current in a C.T. is _________
a) independent of secondary circuit
b) dependent on the secondary circuit
c) depends on the transformation ratio
d) depends on the nominal ratio

View Answer

Answer: a [Reason:] A C.T. is used for the measurement of high magnitude of currents in a circuit, while a P.T. is used for the measurement of high magnitude of voltages in a circuit. Primary current in a C.T. is independent of the secondary circuit conditions.

6. The excitation current of a C.T.
a) varies over a fixed range of operation
b) varies over a wide range of normal operation
c) is fixed over a range of operation
d) is fixed always

View Answer

Answer: b [Reason:] In a potential transformer, the excitation current remains constant under normal operation. While in a current transformer, the excitation current varies over a wide range of operation.

7. Secondary of a P.T. can be open circuited.
a) True
b) False

View Answer

Answer: a [Reason:] In a C.T., the secondary winding must never be open circuited when current is flowing in the primary winding. While in a P.T., the secondary winding can be open circuited without any damage to the circuit.

8. When C.T. is connected in series with a line, a large voltage exists across the primary.
a) True
b) False

View Answer

Answer: b [Reason:] In a P.T., full voltage appears across the primary winding when it is connected across the line. While when a C.T. is connected in series with a line, a very small voltage appears across the primary winding.

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