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Multiple choice question for engineering

Set 1

1. When a ferromagnetic core is inserted into an inductor, what happens to the flux linkage?
a) Increases
b) Decreases
c) Remains the same
d) Becomes zero

View Answer

Answer: a [Reason:] When a ferromagnetic core is introduced into an inductor, its flux increases because the number of magnetic field lines increase due to the introduction of a magnetic within the coil.

2. What happens to the current when a ferromagnetic material is introduced within an inductor?
a) Increases
b) Decreases
c) Remains the same
d) Becomes zero

View Answer

Answer: c [Reason:] When a ferromagnetic is introduced within an inductor, the current remains fairly constant. This is because the current does not depend on the magnetic field.

3. What is the relation between the flux and the magnetizing current when a ferromagnetic core is introduced within the inductor?
a) Directly proportional
b) Inversely proportional
c) Not proportional
d) Current is double of flux

View Answer

Answer: c [Reason:] When a ferromagnetic core is introduced within an inductor the flux changes rapidly, whereas the current changes at the same pace. Hence the two are not proportional.

4. What happens to the effective inductance when a ferromagnetic core is introduced?
a) Increases
b) Decreases
c) Remains the same
d) Becomes zero

View Answer

Answer: a [Reason:] The effective inductance increases when a ferromagnetic core is introduced within an inductor because the flux increases. Inductance varies directly with the flux hence it increases.

5. A laminated steel ring is wound with 200 turns. When the magnetizing current varies between 5 and 7 A, the magnetic flux varies between 760 and 800 ∫Wb. Calculate the incremental inductance of the coil.
a) 40H
b) 40mH
c) 0.004H
d) 0.004mH

View Answer

Answer: c [Reason:] From the formula of incremental inductance, we know that: L=(Change in flux/Change in current)*Number of turns Substituting the values from the given question, we get L= 0.004H.

6. Calculate the number of turns in an inductor with a ferromagnetic core when the inductance is 0.004H, the current changes from 5A to 7A and the flux changes from 760 to 800 ∫Wb.
a) 100
b) 200
c) 300
d) 400

View Answer

Answer: b [Reason:] From the formula of incremental inductance, we know that: L=(Change in flux/Change in current)*Number of turns Substituting the values from the given question, we get N=200.

7. Calculate the change in current in an inductor having inductance 0.004H, number of turns is 200 and the flux changes from 760 to 800 ∫Wb.
a) 2A
b) 4A
c) 6A
d) 8A

View Answer

Answer: a [Reason:] From the formula of incremental inductance, we know that: L=(Change in flux/Change in current)*Number of turns Substituting the values from the given question, we get change in current= 2A.

8. Calculate the initial current in an inductor having inductance 0.004H, number of turns is 200 and the flux changes from 760 to 800 ∫Wb. Current changes to 7A.
a) 10A
b) 2A
c) 3A
d) 5A

View Answer

Answer: c [Reason:] From the formula of incremental inductance, we know that: L=(Change in flux/Change in current)*Number of turns Substituting the values from the given question, we get change in current= 2A. Change in current= final current- initial current. 2=7-initial current. Initial current= 5A.

9. Calculate the chance in flux of an inductor having inductance 0.004H, number of turns is 200 and the current changes from 5A to 7A.
a) 20 ∫Wb
b) 40∫Wb
c) 60∫Wb
d) 80∫Wb

View Answer

Answer: b [Reason:] From the formula of incremental inductance, we know that: L=(Change in flux/Change in current)*Number of turns Substituting the values from the given question, we get change in flux= 40∫Wb.

10. Calculate the final flux in an inductor having inductance 0.004H, number of turns is 200 and the current changes from 5A to 7A. The initial flux is 760∫Wb.
a) 200∫Wb
b) 400∫Wb
c) 600∫Wb
d) 800∫Wb

View Answer

Answer: d [Reason:] From the formula of incremental inductance, we know that: L=(Change in flux/Change in current)*Number of turns Substituting the values from the given question, we get change in flux= 40∫Wb. Change in flux= final flux- initial flux. Thus final flux= 800∫Wb.

Set 2

1. As the number of turns in the coil increases, what happens to the inductance of the coil?
a) Increases
b) Decreases
c) Remains the same
d) Becomes zero

View Answer

Answer: a [Reason:] Inductance is directly proportional to the square of the number of turns in the coil, hence as the number of turns increases, inductance also increases.

2. What happens to the inductance when the magnetic field strength decreases?
a) Increases
b) Decreases
c) Remains the same
d) Becomes zero

View Answer

Answer: b [Reason:] Inductance is directly proportional to the magnetic field strength in the coil, hence as the magnetic field strength increases, inductance decreases.

3. What happens to the inductance when the current in the coil becomes double its original value?
a) Becomes half
b) Becomes four times
c) Becomes infinity
d) Becomes double

View Answer

Answer: d [Reason:] The formula for magnetic field strength in a coil is: H=iN/l The inductance is: directly proportional to magnetic field strength, hence as the current value doubles, the inductance also doubles.

4. When the coil is wrapped around a ferromagnetic core, why is it difficult to determine the inductance?
a) The variation of flux is no longer proportional to the variation of current
b) Current does not exist in the coil
c) Flux does not exist in the coil
d) The value of current is too large to measure

View Answer

Answer: a [Reason:] When a coil is wrapped around a ferromagnetic core, it is difficult to determine the inductance because the variation of flux is no longer proportional to the variation of current.

5. What happens to the inductance as the area of cross section of the coil increases?
a) Increases
b) Decreases
c) Remains the same
d) Becomes zero

View Answer

Answer: a [Reason:] The formula for inductance is: L=4*pi*10-7*A*N2/l, hence as the area of cross section A increases, the inductance also increases.

6. What happens to the inductance as the length of the magnetic circuit increases?
a) Increases
b) Decreases
c) Remains the same
d) Becomes zero

View Answer

Answer: b [Reason:] The formula for inductance is: L=4*pi*10-7*A*N2/l, hence as the length of the magnetic circuit l increases, the inductance decreases.

7. Among the following, which is the right formula for inductance?
a) L=emf*t/I
b) L=emf/t*I
c) L=emf*I/t
d) L=emf*t*I

View Answer

Answer: a [Reason:] The average emf induced is proportional to the current per unit time, the constant of proportionality being L. Hence emf=LI/t. Making L the subject of the formula, we get: L=emf*t/I.

8. The unit for inductance is ___________
a) Ohm
b) Henry
c) A/m
d) A/s

View Answer

Answer: b [Reason:] The unit of induction is named after a famous scientist Joseph Henry who independently discovered electromagnetic induction.

9. For a coil having a magnetic circuit of constant reluctance, the flux is ___________ to the current.
a) Directly proportional
b) Inversely proportional
c) Not related
d) Very large compared to

View Answer

Answer: a [Reason:] For a coil having a magnetic circuit of constant reluctance, the flux is directly proportional to the current.

10. What is the unit for inductive reactance?
a) Henry
b) Ohm
c) Farad
d) Volts

View Answer

Answer: b [Reason:] Inductive reactance is nothing but the impedance. Impedance is the AC equivalent of resistance, hence the unit for inductive reactance is ohm.

Set 3

1. The energy stored in the capacitor is of _________ nature.
a) Electrostatic
b) Magnetic
c) Neither electrostatic nor magnetic
d) Either electrostatic or magnetic

View Answer

Answer: a [Reason:] The energy stored in a capacitor is in the form of electrostatic energy whereas the energy stored in the inductor is in the form of magnetic energy.

2. The energy stored in the inductor is of _________ nature.
a) Electrostatic
b) Magnetic
c) Neither electrostatic nor magnetic
d) Either electrostatic or magnetic

View Answer

Answer: b [Reason:] The energy stored in a capacitor is in the form of electrostatic energy whereas the energy stored in the inductor is in the form of magnetic energy.

3. At resonance, the circuit appears __________
a) Inductive
b) Capacitive
c) Either inductive or capacitive
d) Resistive

View Answer

Answer: d [Reason:] At resonance, the circuit appears resistive because the capacitive and inductive energies are equal to each other.

4. At resonance, the capacitive energy is ___________ inductive energy.
a) Greater than
b) Less than
c) Equal to
d) Depends on the circuit

View Answer

Answer: c [Reason:] At resonance, the capacitive energy is equal to the inductive energy and the circuit appears to be resistive in nature.

5. At resonance, electrostatic energy is ___________ the magnetic energy.
a) Greater than
b) Less than
c) Equal to
d) Depends on the circuit

View Answer

Answer: c [Reason:] At resonance, the capacitive energy is equal to the inductive energy and the circuit appears to be resistive in nature. The capacitor stores electrostatic energy and the inductor stores magnetic energy hence they are equal.

6. The maximum magnetic energy stored in an inductor at any instance is?
a) E=LIm2/2
b) E=LIm/2
c) E=LIm2
d) E=LIm2*2

View Answer

Answer: a [Reason:] At any instant, the magnetic energy stored in an inductor is E=LIm2/2, where Im is the maximum current and L is the value of the inductor.

7. The maximum electrostatic energy stored in a capacitor at any instance is?
a) CVm2
b) 1/2*CVm2
c) CVm
d) CVm/2

View Answer

Answer: b [Reason:] The maximum electrostatic energy stored in a capacitor at any instance is 1/2*CVm2, where C is the capacitance value and Vm is the peak voltage.

8. Q is the ratio of?
a) Active power to reactive power
b) Reactive power to active power
c) Reactive power to average power
d) Reactive power to capacitive power

View Answer

Answer: c [Reason:] Q is the ratio of the reactive power to the average power. The reactive power is due to the inductance or capacitance and the average power is due to the resistance.

9. Find the value of Q if the reactive power is 10W and the average power is 5W.
a) 10
b) 5
c) 2
d) 1

View Answer

Answer: c [Reason:] Q is the ratio of the reactive power to the average power. Substituting the given values from the question, we get Q=2.

10. Find the reactive power when the average power is 5W and Q=2.
a) 10W
b) 5W
c) 2W
d) 1W

View Answer

Answer: a [Reason:] Q is the ratio of the reactive power to the average power. Substituting the given values from the question, we get reactive power= 10W.

Set 4

1. In an impedance parallel network, the reactive component will ____________ the voltage by 90 degrees.
a) Lead
b) Lag
c) Either lead or lag
d) Depends on the circuit

View Answer

Answer: c [Reason:] In an impedance parallel network the reactive component will either lead or lag the voltage by 90 degrees.

2. In an impedance parallel network the reactive component will either lead or lag the voltage by _________ degrees.
a) 0
b) 90
c) 45
d) 180

View Answer

Answer: b [Reason:] In an impedance parallel network the reactive component will either lead or lag the voltage by 90 degrees.

3. In an impedance parallel network the reactive component will either lead or lag the ________ by 90 degrees.
a) Voltage
b) Current
c) Either voltage or current
d) Cannot be determined

View Answer

Answer: a [Reason:] In an impedance parallel network the reactive component will either lead or lag the voltage by 90 degrees.

4. The reactive component in an impedance parallel circuit leads the voltage when the current _________ the voltage.
a) Leads
b) Lags
c) Either leads or lags
d) Cannot be determined

View Answer

Answer: a [Reason:] The reactive component in an impedance parallel circuit leads the voltage when the current leads the voltage.

5. The active component in an impedance parallel circuit will __________ the voltage.
a) Leads
b) Lags
c) Be in phase with
d) Either leads or lags

View Answer

Answer: c [Reason:] The active component in an impedance parallel network will always be in phase with the voltage in the circuit.

6. The phase difference between the active component of an impedance parallel circuit and the voltage in the network is __________
a) 0
b) 90
c) 180
d) 360

View Answer

Answer: a [Reason:] The active component in an impedance parallel network will always be in phase with the voltage in the circuit. Hence the phase difference is 0.

7. The quadrature component is also known as?
a) Active component
b) Reactive component
c) Either active or reactive component
d) Neither active nor reactive component

View Answer

Answer: b [Reason:] The quadrature component is also known as the reactive component because the reactive component forms a quadrature with the voltage.

8. What is the phase relation between IL and V from the following circuit?
basic-electrical-engineering-questions-answers-parallel-impedance-circuits-q8
a) IL lags V
b) IL leads V
c) IL and V are in phase
d) No relation

View Answer

Answer: a [Reason:] IL is the current across the inductor and we know that the current across the inductor always lags the voltage across it. Hence IL lags V.

9. What is the expression for the current in the inductor from the following circuit?
basic-electrical-engineering-questions-answers-parallel-impedance-circuits-q8
a) V/I
b) V/XL
c) 0
d) Cannot be determined

View Answer

Answer: b [Reason:] In the given circuit, the voltage across the inductor is the same as the source voltage as they are connected in parallel. The current in the inductor is IL hence IL=V/XL.

10. Find the total current if IL=2A and Ir=8A.
basic-electrical-engineering-questions-answers-parallel-impedance-circuits-q8
a) 3A
b) -3A
c) 7A
d) 10A

View Answer

Answer: d [Reason:] We know that I=IR+IL. Substituting the values from the question, we get I=10A.

Set 5

1. If two bulbs are connected in parallel and one bulb blows out, what happens to the other bulb?
a) The other bulb blows out as well
b) The other bulb continues to glow with the same brightness
c) The other bulb glows with increased brightness
d) The other bulb stops glowing

View Answer

Answer: b [Reason:] In a parallel circuit, if one bulb blows out, it acts as an open circuit. Current does not flow in that branch but it continues to flow in the other branch hence the bulb continues to glow.

2. Calculate the current across the 20 ohm resistor.
basic-electrical-engineering-questions-answers-parallel-networks-q2
a) 10A
b) 20A
c) 6.67A
d) 36.67A

View Answer

Answer: a [Reason:] I=V/R. Since parallel circuit voltage remains constant across all resistors. Hence across the 20 ohm resistor, I=200/20=10A.

3. In a parallel circuit, with a number of resistors, the voltage across each resistor is ________
a) The same for all resistors
b) Is divided equally among all resistors
c) Is divided proportionally across all resistors
d) Is zero for all resistors

View Answer

Answer: a [Reason:] In parallel circuits, the current across the circuits vary whereas the voltage remains the same.

4. The current in each branch of a parallel circuit is proportional to_______
a) The amount of time the circuit is on for
b) Proportional to the value of the resistors
c) Equal in all branches
d) Proportional to the power in the circuit

View Answer

Answer: b [Reason:] In a parallel circuit, I=V/R hence the value of current id proportional to the value of the resistance.

5. Calculate the total current in the circuit.
basic-electrical-engineering-questions-answers-parallel-networks-q5
a) 20A
b) 10A
c) 12A
d) 15A

View Answer

Answer: b [Reason:] The 1 ohm and 2 ohm resistor are in series which is in parallel to the 3 ohm resistor. The equivalent of these resistances is in series with the 4 ohm and 5 ohm resistor. Total R=12 ohm. I=V/R= 120/12= 10A.

6. The voltage across the open circuit is?
basic-electrical-engineering-questions-answers-parallel-networks-q6
a) 100V
b) Infinity
c) 90V
d) 0V

View Answer

Answer: a [Reason:] The voltage across all branches in a parallel circuit is the same as that of the source voltage. Hence the voltage across the 10 ohm resistor and the open circuit is the same=100V.

7. The voltage across the short is?
basic-electrical-engineering-questions-answers-parallel-networks-q7
a) 135V
b) Infinity
c) Zero
d) 11.25V

View Answer

Answer: c [Reason:] The voltage across a short is always equal to zero whether it is connected in seroes or parallel.

8. If the current in the circuit=5A, find the value of x.
basic-electrical-engineering-questions-answers-parallel-networks-q8
a) 27 ohm
b) 5 ohm
c) 12 ohm
d) 135 ohm

View Answer

Answer: a [Reason:] R=V/I. In this circuit I=5A and V=135V. Therefore, R=135/5=27 ohm.

9. The currents in the three branches of a parallel circuit are 3A, 4A and 5A. What is the current leaving it?
a) 0A
b) Insufficient data provided
c) The largest one among the three values
d) 12A

View Answer

Answer: d [Reason:] The total current leaving a node is the same as the current that enters it. Total I=I1+I2+I3=3+4+5=12A.

10. The total resistance between A and B are?
basic-electrical-engineering-questions-answers-parallel-networks-q10
a) 20 ohm
b) 5 ohm
c) 80 ohm
d) 0 ohm

View Answer

Answer: b [Reason:] The resistors are connected in parallel, hence the equivalent resistance= 1/(1/20=1/20+1/20+1/20)=5A.

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