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Multiple choice question for engineering

Set 1

1. Transformation ratio of an instrument is defined as
a) ratio of primary to secondary phasor
b) ratio of secondary to primary phasor
c) reciprocal of the primary phasor
d) reciprocal of the secondary phasor

View Answer

Answer: a [Reason:] For an instrument transformer, the transformation ratio is defined as the ratio of the magnitude of the actual primary phasor to the magnitude of the secondary phasor.

2. For a C.T. the transformation ratio is given by the relation
a) R = IsIp
b) R = IpIs
c) R = 1Ip
d) R = Ip

View Answer

Answer: b [Reason:] In a current transformer, the transformation ratio is given by the ratio of the magnitude of the actual primary current to the magnitude of the actual secondary current. R = IpIs where, R is the transformation ratio Ip is the actual primary winding current Is is the actual secondary winding current.

3. For a P.T. the transformation ratio is given by the relation
a) R = VsVp
b) R = 1Vs
c) R = VpVs
d) R = Vp

View Answer

Answer: c [Reason:] In a potential transformer, the transformation ratio is given by the ratio of the magnitude of the actual primary current to the magnitude of the actual secondary current. R = VpVs where, R is the transformation ratio Vp is the actual primary winding voltage Vs is the actual secondary winding voltage.

4. Nominal ratio of an instrument transformer is defined as the __________
a) reciprocal of the rated primary value
b) ratio of rated secondary value to primary value
c) reciprocal of the rated secondary value
d) ratio of rated primary value to secondary value

View Answer

Answer: d [Reason:] In an instrument transformer, nominal ratio is defined as the ratio of the rated primary current or voltage to the rated secondary winding current or voltage.

5. For a C.T. the nominal ratio is given by the relation.
electrical-measurements-questions-answers-ratios-instrument-transformers-q5

View Answer

Answer: a [Reason:] In a current transformer, the transformation ratio is given by the ratio of the magnitude of the actual primary current to the magnitude of the actual secondary current. electrical-measurements-questions-answers-ratios-instrument-transformers-q5a where, R is the transformation ratio Ip(rated) is the rated primary winding current Is(rated) is the rated secondary winding current.

6. For a P.T. the nominal ratio is given by the relation
electrical-measurements-questions-answers-ratios-instrument-transformers-q6

View Answer

Answer: b [Reason:] In a potential transformer, the transformation ratio is given by the ratio of the magnitude of the actual primary voltage to the magnitude of the actual secondary voltage. electrical-measurements-questions-answers-ratios-instrument-transformers-q6a where, R is the transformation ratio Vp(rated) is the rated primary winding voltage Vs(rated) is the rated secondary winding voltage.

7. Ratio correction factor is defined as _________
a) reciprocal of nominal ratio
b) ratio of nominal ratio to transformation ratio
c) ratio of transformation ratio to nominal ratio
d) reciprocal of transformation ratio

View Answer

Answer: c [Reason:] The ratio correction factor for an instrument transformer is defined as the ratio of the transformation ratio to the nominal ratio. R.C.F = RKn where, R.C.F is the ratio correction factor R is the transformation ratio Kn is the nominal ratio.

8. For a C.T. the turns ratio is defined as the _________
a) n = NpNs
b) n = 1Np
c) n = Ns
d) n = NsNp

View Answer

Answer: d [Reason:] For a current transformer, the turns ratio is defined as the ratio of the number of turns in the secondary winding to the number of turns in the primary winding. n = NsNp where, n is the turns ratio Ns is the secondary turns Np is the primary turns.

9. For a P.T. the turns ratio is defined as the _________
a) n = NpNs
b) n = 1Np
c) n = Ns
d) n = NsNp

View Answer

Answer: a [Reason:] For a potential transformer, the turns ratio is defined as the ratio of the number of turns in the primary winding to the number of turns in the secondary winding. n = NpNs where, n is the turns ratio Np is the primary turns Ns is the secondary turns.

Set 2

1. Winding resistance of a P.T. can be reduced by _________
a) using thick conductors
b) decreasing the length of the winding
c) shorting the primary and secondary windings
d) using thin conductors

View Answer

Answer: a [Reason:] In a potential transformer, the winding resistance is usually minimised by using thick conductors and by making use of small length for the turns.

2. Leakage reactance is minimised by _________
a) using thin conductors
b) reducing leakage flux
c) increasing flux density
d) shorting the windings

View Answer

Answer: b [Reason:] By maintaining the primary and secondary windings together in a P.T. and also by reducing the leakage flux, we can minimise the leakage reactance.

3. High flux density is due to less turns
a) True
b) False

View Answer

Answer: a [Reason:] In a P.T., a high flux density in the core, gives rise to a less number of turns. This in turn results in a lower leakage reactance.

4. Ratio error in a P.T. depends on _________
a) secondary current
b) primary voltage
c) secondary current
d) turns ratio

View Answer

Answer: c [Reason:] In a P.T., the difference between actual ratio and turns ratio is given by the relation, electrical-measurements-questions-answers-reduction-errors-potential-transformers-q4 where, R is the ratio error n is the turns ratio Is is the secondary winding current Ie is the iron loss component Im is the magnetising component It is seen from the above equation that the ratio error in a P.T. depends on the secondary current, magnetising and iron loss components of current.

5. In a P.T. values of components of currents are negligible.
a) True
b) False

View Answer

Answer: b [Reason:] In a C.T. the various components of current such as magnetising current, iron loss component of current are almost comparable in magnitude with the value of the load current.

6. Ratio error can be minimised by _________
a) reducing the turns
b) reducing the current
c) increasing the voltage
d) using a good core material

View Answer

Answer: d [Reason:] By making use of a good quality core material, low value of flux density and following required precautions in the core assembly we can minimise the value of the ratio error.

7. Another method of eliminating the ratio error is _________
a) by reducing secondary turns
b) by increasing the primary turns
c) by increasing secondary turns
d) by reducing the primary turns

View Answer

Answer: a [Reason:] In a P.T., at no load, we get electrical-measurements-questions-answers-reduction-errors-potential-transformers-q7 where, R is the ratio error n is the turns ratio Is is the secondary winding current Ie is the iron loss component Im is the magnetising component From the above equation it is seen that to reduce the ratio error, actual ratio and nominal ratio must be made equal. This can be done by reducing the secondary turns.

8. How is the voltage ratio dependent on the frequency?
a) they are independent of each other
b) they aid each other
c) they oppose each other
d) depends on the setup of the circuit

View Answer

Answer: c [Reason:] As the voltage ratio changes, the frequency also changes. It depends on the relative value of the core loss component Io as well as the leakage reactance. The effects due to the voltage ratio and the change in frequency oppose each other.

Set 3

1. Schering bridge is one of the most widely used AC bridges.
a) True
b) False

View Answer

Answer: a [Reason:] Schering bridge is an AC bridge used for the measurement of unknown capacitance, dielectric loss and power factor. It is one of the most commonly used AC bridges.

2. Schering bridge is used for _________
a) low voltages only
b) low and high voltages
c) high voltages only
d) intermediate voltages only

View Answer

Answer: b [Reason:] Schering bridge is used for both low as well as high voltages. A particular bridge connection is used for low voltage. High voltages employ the use of a different type of Schering bridge.

3. Power factor of a Schering bridge is _________
a) p.f. = sin∅x = ZxRx
b) p.f. = cot∅x = RxZx
c) p.f. = cos∅x = RxZx
d) p.f. = tan∅x = RxZx

View Answer

Answer: c [Reason:] The power factor of the RC combination in a Schering bridge is given by the relation p.f. = cos∅x = RxZx . where, Rx is the series resistance Zx is the series impedance comprising of Rx and Cx.

4. For phase angles close to 90°, the power factor of the bridge is _________
a) p.f. = ωRx
b) p.f. = ωCx
c) p.f. = Rx Cx
d) p.f. = ωRx Cx

View Answer

Answer: d [Reason:] When phase angle reaches 90°, reactance equals the impedance and the power factor of the bridge is calculated using the relation, electrical-measurements-questions-answers-schering-bridge-q4

5. For a series RC circuit, what is δ?
a) voltage between series RC combination and C
b) voltage between series RC combination
c) voltage across C
d) voltage across R

View Answer

Answer: a [Reason:] In a series RC circuit, δ refers to the angle between the series combination of Rx, Cx and the voltage across the capacitance Cx. δ is also known as the loss angle.

6. What is the expression for the loss angle?
a) tan⁡ δ = ωR4
b) tan⁡ δ = ωR4 C4
c) tan⁡ δ = ωC4
d) tan⁡ δ = R4 C4

View Answer

Answer: b [Reason:] The expression for the loss angle can be computed as the ratio of the tangent of the voltage drop across resistance Rx to the voltage drop across the capacitance Cx. electrical-measurements-questions-answers-schering-bridge-q6

7. Quality factor is given by the expression
a) Q = 1R
b) Q = R
c) Q = XR
d) Q = XR

View Answer

Answer: c [Reason:] The quality factor the Schering bridge circuit is defined as Q = XR. where, X = 1wC is the capacitive impedance.

8. Dissipation factor is the reciprocal of quality factor.
a) True
b) False

View Answer

Answer: a [Reason:] Dissipation factor for a circuit is defined as the reciprocal of the quality factor. It is given by the expression Q = 1wCR. It basically provides information about the quality of a capacitor.

9. Commercial Schering bridge can be used for the measurement of capacitances
a) from 10pF to 0.1nF
b) from 100pF to 1μF
c) from 50nF to 10mF
d) from 25mF to 5F

View Answer

Answer: b [Reason:] Commercial Schering bridges are used for the measurement of capacitances in the range of a few pico farads to a few micro farads. Accuracy varies in the range of –2% to +2%.

10. A Schering bridge can be used for the
a) measuring voltages
b) measuring currents
c) testing capacitors
d) protecting the circuit from temperature rises

View Answer

Answer: c [Reason:] A Schering bridge can be used with both low voltage as well as high voltages. A Schering bridge is basically used for the measurement of small capacitances at low voltages with high precision.

Set 4

1. When bridge is balanced, what is the current flowing through the galvanometer?
a) 0
b) depends on the ratio arms R1 and R2
c) varies by a factor of 2
d) depends on the type of null detector used

View Answer

Answer: a [Reason:] Under bridge balance condition, no current flows through the galvanometer. Current flow is independent of the values of ratio arms R1 and R2.

2. Amount of deflection of the galvanometer depends on _________
a) resistance of the ratio arms
b) sensitivity
c) current flowing through the bridge
d) emf across the circuit

View Answer

Answer: b [Reason:] The amount of deflection of the galvanometer depends upon its sensitivity. Resistance of the ratio arms does not affect the amount of deflection of the galvanometer.

3. Sensitivity is defined as _________
a) amount of voltage per unit current
b) amount of power per unit voltage
c) amount of resistance per unit voltage
d) amount of deflection per unit current

View Answer

Answer: d [Reason:] Sensitivity is expressed as electrical-measurements-questions-answers-sensitivity-wheatstone-bridge-q3 Thus sensitivity is defined as the amount of deflection per unit current.

4. Sensitivity is expressed in
a) cm/A
b) m/mA
c) mm/µA
d) inch/nA

View Answer

Answer: c [Reason:] electrical-measurements-questions-answers-sensitivity-wheatstone-bridge-q3 where, deflection is in mm and current is in µA. So the unit of sensitivity is mm/ µA.

5. What is the relation between the sensitivity and deflection for a galvanometer?
a) directly proportional
b) inversely proportional
c) independant of each other
d) depends on the type of galvanometer used

View Answer

Answer: a [Reason:] electrical-measurements-questions-answers-sensitivity-wheatstone-bridge-q3 Thus we see that sensitivity is directly proportional to the deflection.

6. The voltage sensitivity of a galvanometer is given by _________
a) Sv = eθ
b) Sv = θe
c) Sv = 1e
d) Sv = 1θ

View Answer

Answer: b [Reason:] electrical-measurements-questions-answers-sensitivity-wheatstone-bridge-q6 Voltage sensitivity is defined as the amount of deflection per unit voltage and is given by the relation Sv = θe.

7. Unit of voltage sensitivity is _________
a) volts per degrees
b) amps per ohms
c) degrees per volts
d) watts per amps

View Answer

Answer: c [Reason:] electrical-measurements-questions-answers-sensitivity-wheatstone-bridge-q6 So the unit of voltage sensitivity is degrees per volts as deflection is measured in degrees and voltage is in volts.

8. Bridge sensitivity is defined as
electrical-measurements-questions-answers-sensitivity-wheatstone-bridge-q8

View Answer

Answer: d [Reason:] The bridge sensitivity is defined as the amount of deflection of the galvanometer per unit fractional change in the unknown resistance. electrical-measurements-questions-answers-sensitivity-wheatstone-bridge-q8a Here ∆R/R denotes the fractional change in the unknown resistance.

9. Maximum sensitivity occurs when
a) R3R4 = 1
b) R2R4 = 1
c) R1R2 = 1
d) R3R2 = 1

View Answer

Answer: a [Reason:] Under a small unbalance condition, the bridge sensitivity equation becomes electrical-measurements-questions-answers-sensitivity-wheatstone-bridge-q9 Here E is the emf of the circuit. For maximum bridge sensitivity, we get R3=R4.

Set 5

1. Wheatstone bridge consists of _________
a) 4 resistive arms
b) 2 resistive arms
c) 6 resistive arms
d) 8 resistive arms

View Answer

Answer: a [Reason:] A Wheatstone bridge essentially consists of 4 resistive arms. The arms are such that two resistances appear across each end.

2. A galvanometer is used as a _________
a) current source
b) voltage source
c) null detector
d) input impedance

View Answer

Answer: c [Reason:] A galvanometer is used as a null detector to detect the flow of current across the ends of the two opposite junctions of the circuit. Voltage source is used for providing the required dc supply to the bridge.

3. The opposite two ends of a Wheatstone bridge consist of _________
a) voltage and current source
b) e.m.f and null detector
c) resistance and capacitance
d) inductance and impedance

View Answer

Answer: b [Reason:] The two opposite ends of a Wheatstone bridge circuit consists of a source of e.m.f and a null detector. Four arms of a Wheatstone bridge consist of resistances. Inductance and capacitance do not appear in a Wheatstone bridge.

4. The arms consisting of the resistances R1 and R2 are called _________
a) resistance arms
b) impedance arms
c) source arms
d) ratio arms

View Answer

Answer: d [Reason:] The arms consisting of the two resistances R1 and R2 are known as the resistance arms. Sources do not appear on the arms of the bridge and they are connected across opposite ends. Wheatstone bridge is purely resistive in nature.

5. The arm consisting of the standard known resistance R3 is known as __________
a) standard arm
b) resistance arm
c) accurate arm
d) known arm

View Answer

Answer: a [Reason:] The arm consisting of the standard known resistance R3 is known as the standard arm. By making use of this resistance value the unknown resistance can be determined using the balance condition.

6. Resistance R4 is known as ________
a) standard resistance
b) unknown resistance to be measured
c) resistance arm
d) input resistance

View Answer

Answer: b [Reason:] R4 is the unknown resistance whose value has to be found by comparison with a standard. R3 is known as the standard resistance. Resistance arm comprises of four resistances including R1, R2, R3, and R4.

7. What is connected between the two ends of a Wheatstone bridge?
a) current and voltage source
b) ammeter and voltmeter
c) battery and galvanometer
d) ohmmeter and wattmeter

View Answer

Answer: c [Reason:] A battery is connected between the two ends of the Wheatstone bridge while a galvanometer is connected between the opposite two ends of the circuit. Ammeter is connected in series with the circuit.

8. Wheatstone bridge works on the principle of ________
a) full deflection
b) partial deflection
c) no deflection
d) null deflection

View Answer

Answer: d [Reason:] The Wheatstone bridge works on the principle of null deflection. A galvanometer is usually used for measuring the flow of current in the bridge circuit.

9. The balance condition of a Wheatstone bridge depends on the
a) ratio of arms R1 and R1
b) ratio of arms R3 and R4
c) emf source and null detector
d) current source and power source

View Answer

Answer: a [Reason:] The ratio of the arms R1 and R2 determines the balance condition of a Wheatstone bridge. The balance condition is given by the equation R4 = R3R1R2.

10. Balance condition can be obtained by
a) varying the standard resistance R3
b) varying the resistance arms R1 and R2
c) keeping the unknown resistance R4 constant
d) by making use of a null detector

View Answer

Answer: b [Reason:] The balance condition in a Wheatstone bridge can be obtained by varying the resistances R1 and R2. Null detector is used for determining balance condition.