# 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

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2. For a C.T. the transformation ratio is given by the relation

a) R = ^{Is} ⁄ _{Ip}

b) R = ^{Ip} ⁄ _{Is}

c) R = ^{1} ⁄ _{Ip}

d) R = I_{p}

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^{Ip}⁄

_{Is}where, R is the transformation ratio I

_{p}is the actual primary winding current I

_{s}is the actual secondary winding current.

3. For a P.T. the transformation ratio is given by the relation

a) R = ^{Vs} ⁄ _{Vp}

b) R = ^{1} ⁄ _{Vs}

c) R = ^{Vp} ⁄ _{Vs}

d) R = V_{p}

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^{Vp}⁄

_{Vs}where, R is the transformation ratio V

_{p}is the actual primary winding voltage V

_{s}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

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5. For a C.T. the nominal ratio is given by the relation.

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_{p(rated)}is the rated primary winding current I

_{s(rated)}is the rated secondary winding current.

6. For a P.T. the nominal ratio is given by the relation

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_{p(rated)}is the rated primary winding voltage V

_{s(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

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^{R}⁄

_{Kn}where, R.C.F is the ratio correction factor R is the transformation ratio K

_{n}is the nominal ratio.

8. For a C.T. the turns ratio is defined as the _________

a) n = ^{Np} ⁄ _{Ns}

b) n = ^{1} ⁄ _{Np}

c) n = N_{s}

d) n = ^{Ns} ⁄ _{Np}

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^{Ns}⁄

_{Np}where, n is the turns ratio N

_{s}is the secondary turns N

_{p}is the primary turns.

9. For a P.T. the turns ratio is defined as the _________

a) n = ^{Np} ⁄ _{Ns}

b) n = ^{1} ⁄ _{Np}

c) n = N_{s}

d) n = ^{Ns} ⁄ _{Np}

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^{Np}⁄

_{Ns}where, n is the turns ratio N

_{p}is the primary turns N

_{s}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

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2. Leakage reactance is minimised by _________

a) using thin conductors

b) reducing leakage flux

c) increasing flux density

d) shorting the windings

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3. High flux density is due to less turns

a) True

b) False

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4. Ratio error in a P.T. depends on _________

a) secondary current

b) primary voltage

c) secondary current

d) turns ratio

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_{s}is the secondary winding current I

_{e}is the iron loss component I

_{m}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

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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

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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

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_{s}is the secondary winding current I

_{e}is the iron loss component I

_{m}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

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## Set 3

1. Schering bridge is one of the most widely used AC bridges.

a) True

b) False

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2. Schering bridge is used for _________

a) low voltages only

b) low and high voltages

c) high voltages only

d) intermediate voltages only

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3. Power factor of a Schering bridge is _________

a) p.f. = sin∅_{x} = ^{Zx}⁄_{Rx }

b) p.f. = cot∅_{x} = ^{Rx}⁄_{Zx }

c) p.f. = cos∅_{x} = ^{Rx}⁄_{Zx }

d) p.f. = tan∅_{x} = ^{Rx}⁄_{Zx }

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_{x}=

^{Rx}⁄

_{Zx }. where, R

_{x}is the series resistance Z

_{x}is the series impedance comprising of Rx and C

_{x}.

4. For phase angles close to 90°, the power factor of the bridge is _________

a) p.f. = ωR_{x}

b) p.f. = ωC_{x}

c) p.f. = R_{x} C_{x}

d) p.f. = ωR_{x} C_{x}

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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

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_{x}, C

_{x}and the voltage across the capacitance C

_{x}. δ is also known as the loss angle.

6. What is the expression for the loss angle?

a) tan δ = ωR_{4}

b) tan δ = ωR_{4} C_{4}

c) tan δ = ωC_{4}

d) tan δ = R_{4} C_{4}

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_{x}to the voltage drop across the capacitance C

_{x}.

7. Quality factor is given by the expression

a) Q = ^{1}⁄_{R}

b) Q = R

c) Q = ^{X}⁄_{R}

d) Q = XR

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^{X}⁄

_{R}. where, X =

^{1}⁄

_{wC}is the capacitive impedance.

8. Dissipation factor is the reciprocal of quality factor.

a) True

b) False

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^{1}⁄

_{wCR}. 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

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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

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## Set 4

1. When bridge is balanced, what is the current flowing through the galvanometer?

a) 0

b) depends on the ratio arms R_{1} and R_{2}

c) varies by a factor of 2

d) depends on the type of null detector used

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_{1}and R

_{2}.

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

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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

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4. Sensitivity is expressed in

a) cm/A

b) m/mA

c) mm/µA

d) inch/nA

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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

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6. The voltage sensitivity of a galvanometer is given by _________

a) S_{v} = ^{e}⁄_{θ}

b) S_{v} = ^{θ}⁄_{e}

c) S_{v} = ^{1}⁄_{e}

d) S_{v} = ^{1}⁄_{θ}

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_{v}=

^{θ}⁄

_{e}.

7. Unit of voltage sensitivity is _________

a) volts per degrees

b) amps per ohms

c) degrees per volts

d) watts per amps

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8. Bridge sensitivity is defined as

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9. Maximum sensitivity occurs when

a) ^{R3} ⁄ _{R4} = 1

b) ^{R2} ⁄ _{R4} = 1

c) ^{R1} ⁄ _{R2} = 1

d) ^{R3} ⁄ _{R2} = 1

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_{3}=R

_{4}.

## Set 5

1. Wheatstone bridge consists of _________

a) 4 resistive arms

b) 2 resistive arms

c) 6 resistive arms

d) 8 resistive arms

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2. A galvanometer is used as a _________

a) current source

b) voltage source

c) null detector

d) input impedance

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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

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4. The arms consisting of the resistances R_{1} and R_{2} are called _________

a) resistance arms

b) impedance arms

c) source arms

d) ratio arms

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_{1}and R

_{2}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 R_{3} is known as __________

a) standard arm

b) resistance arm

c) accurate arm

d) known arm

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_{3}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 R_{4} is known as ________

a) standard resistance

b) unknown resistance to be measured

c) resistance arm

d) input resistance

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_{4}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

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8. Wheatstone bridge works on the principle of ________

a) full deflection

b) partial deflection

c) no deflection

d) null deflection

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9. The balance condition of a Wheatstone bridge depends on the

a) ratio of arms R_{1} and R_{1}

b) ratio of arms R_{3} and R_{4}

c) emf source and null detector

d) current source and power source

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_{1}and R

_{2}determines the balance condition of a Wheatstone bridge. The balance condition is given by the equation R

_{4}=

^{R3R1}⁄

_{R2}.

10. Balance condition can be obtained by

a) varying the standard resistance R_{3}

b) varying the resistance arms R_{1} and R_{2}

c) keeping the unknown resistance R_{4} constant

d) by making use of a null detector

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_{1}and R

_{2}. Null detector is used for determining balance condition.