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Multiple choice question for engineering

Set 1

1. The charging time constant of a circuit consisting of a capacitor is the time taken for the charge in the capacitor to become __________% of the initial charge.
a) 33
b) 63
c) 37
d) 36

View Answer

Answer: b [Reason:] We know that: Q=Q0(1-e-t/RC). When RC=t, we have: Q=Q0(1-e-1)= 0.63*Q0. Hence the time constant is the time taken for the charge in a capacitive circuit to become 0.63 times its initial charge.

2. The discharging time constant of a circuit consisting of a capacitor is the time taken for the charge in the capacitor to become __________% of the initial charge.
a) 33
b) 63
c) 37
d) 36

View Answer

Answer: c [Reason:] We know that: Q=Q0(e-t /RC). When RC=t, we have: Q=Q0(e-1)= 0.37*Q0. Hence the time constant is the time taken for the charge in a capacitive circuit to become 0.37 times its initial charge.

3. A circuit has a resistance of 2 ohm connected in series with a capacitance of 6F. Calculate the charging time constant.
a) 3
b) 1
c) 12
d) 8

View Answer

Answer: c [Reason:] The charging time constant in a circuit consisting of a capacitor and resistor in series is the product of the resistance and capacitance= 2*6=12.

4. A circuit has a resistance of 5 ohm connected in series with a capacitance of 10F. Calculate the discharging time constant.
a) 15
b) 50
c) 5
d) 10

View Answer

Answer: b [Reason:] The discharging time constant in a circuit consisting of a capacitor and resistor in se-ries is the product of the resistance and capacitance= 5*10=50.

5. What is the value of current in a discharging capacitive circuit if the initial current is 2A at time t=RC.
a) 0.74A
b) 1.26A
c) 3.67A
d) 2.89A

View Answer

Answer: a [Reason:] At time t=RC, that is the time constant, we know that the value of current at that time interval is equal to 37% of the initial charge in the discharging circuit. Hence, I=2*0.37= 0.74A.

6. What is the value of current in a charging capacitive circuit if the initial current is 2A at time t=RC.
a) 0.74A
b) 1.26A
c) 3.67A
d) 2.89A

View Answer

Answer: b [Reason:] At time t=RC, that is the time constant, we know that the value of current at that time interval is equal to 63% of the initial charge in the charging circuit. Hence, I=2*0.63= 1.26A.

7. While discharging, what happens to the current in the capacitive circuit?
a) Decreases linearly
b) Increases linearly
c) Decreases exponentially
d) Increases exponentially

View Answer

Answer: c [Reason:] The equation for the value of current in a discharging capacitive circuit is: I=I0*e-t /RC. From this equation, we can see that the current is exponentially decreasing since e is raised to a negative power.

8. While discharging, what happens to the voltage in the capacitive circuit?
a) Decreases linearly
b) Increases linearly
c) Decreases exponentially
d) Increases exponentially

View Answer

Answer: c [Reason:] The equation for the value of voltage in a discharging capacitive circuit is: V=V0*e-t /RC. From this equation, we can see that the voltage is exponentially decreasing since e is raised to a negative power.

9. While charging, what happens to the current in the capacitive circuit?
a) Decreases linearly
b) Increases linearly
c) Decreases exponentially
d) Increases exponentially

View Answer

Answer: d [Reason:] The equation for the value of current in a charging capacitive circuit is: I=I0*(1-e-t /RC). From this equation, we can see that the current is exponentially increasing since e is raised to a negative power and we are subtracting it from 1. Hence as the value of e-t /RC in-creases, the current increases exponentially.

10. While charging, what happens to the voltage in the capacitive circuit?
a) Decreases linearly
b) Increases linearly
c) Decreases exponentially
d) Increases exponentially

View Answer

Answer: d [Reason:] The equation for the value of voltage in a charging capacitive circuit is: V=V0*(1-e-t /RC). From this equation, we can see that the voltage is exponentially increasing since e is raised to a negative power and we are subtracting it from 1. Hence as the value of e-t /RC in-creases, the voltage increases exponentially.

Set 2

1. In case of Inductive circuit, Frequency is ______________ to the current.
a) Directly proportional
b) Inversely proportional
c) Unrelated
d) Much greater than

View Answer

Answer: b [Reason:] Inductance is inversely proportional to current since, as the inductance increases, current decreases.

2. In a pure inductive circuit, the power factor is?
a) Maximum
b) Minimum
c) 0
d) Infinity

View Answer

Answer: c [Reason:] In a pure inductive circuit, current is lagging by 90 degrees from the voltage. The power factor is the cosine of the angle in between the voltage and the current. If the angle between the voltage and current is 90, then cos90=0. Hence, the power factor is zero.

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 dou-bles, the inductance also doubles.

4. 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.

5. Among the following, which is the right formula for growth in an inductive circuit?
a) VL=V(1-e-t/time constant)
b) VL=V(1-et /time constant)
c) VL=(1-e-t /time constant)
d) VL=V(e-t /time constant)

View Answer

Answer: a [Reason:] The correct formula for growth in an inductive circuit is VL=V(1-e-t /time constant). As the time increases, the current in the inductor increases hence the voltage also increases.

6. The charging time constant of a circuit consisting of an inductor is the time taken for the voltage in the inductor to become __________% of the initial voltage.
a) 33
b) 63
c) 37
d) 36

View Answer

Answer: b [Reason:] We know that: V=V0(1-e-t /time constant). When time constant=t, we have: V=V0(1-e-1)= 0.63*V0. Hence the time constant is the time taken for the charge in an inductive circuit to become 0.63 times its initial charge.

7. What is the time constant of an inductive circuit?
a) LR
b) R/L
c) 1/LR
d) L/R

View Answer

Answer: d [Reason:] The time constant in an inductive circuit is the time taken for the voltage across the inductor to become 63 percent of its initial value. It is given by: Time constant= L/R.

8. Calculate the time constant of an inductive circuit having resistance 5 ohm and inductance 10H.
a) 2s
b) 4s
c) 5s
d)10s

View Answer

Answer: a [Reason:] We know that: Time constant= L/R Substituting the values from the given question, we get time constant= 2s.

9. Calculate the resistance in an inductive circuit whose time constant is 2s-1 and the inductance is 10H.
a) 7ohm
b) 10ohm
c) 2ohm
d) 5ohm

View Answer

Answer: d [Reason:] We know that: Time constant= L/R Substituting the values from the given question, we get R=5ohm.

10. Calculate the inductance in an inductive circuit whose time constant is 2s-1 and the resistance is 5 ohm.
a) 10H
b) 20H
c) 5H
d) 15H

View Answer

Answer: a [Reason:] We know that: Time constant= L/R Substituting the values from the given question, we get L=10H.

Set 3

1. In case of Inductive circuit, Frequency is ______________ to the inductance.
a) Directly proportional
b) Inversely proportional
c) Unrelated
d) Much greater than

View Answer

Answer: a [Reason:] The formula for frequency in an inductive circuit is: XL=2*pi*f*L. Therefore: XL is directly proportional to f.

2. In case of Inductive circuit, Frequency is ______________ to the current.
a) Directly proportional
b) Inversely proportional
c) Unrelated
d) Much greater than

View Answer

Answer: b [Reason:] Inductance is inversely proportional to current since, as the inductance increases, current decreases.

3. In an inductive circuit, when the XL value increases, the circuit power factor?
a) Increases
b) Decreases
c) Remains the same
d) Becomes zero

View Answer

Answer: b [Reason:] The power factor, that is, cos(phi) is equal to the resistance divided by the impedance in the circuit, hence as impedance increases, the power factor decreases.

4. If the current and voltage are 90 degree out of phase, the power factor will be?
a) 0
b) Infinity
c) 1
d) Insufficient information provided

View Answer

Answer: a [Reason:] The power factor is the cosine of the angle in between the voltage and the current. If the angle between the voltage and current is 90, then cos90=0. Hence, the power factor is zero.

5. In a pure inductive circuit, the power factor is __________
a) Maximum
b) Minimum
c) 0
d) Infinity

View Answer

Answer: c [Reason:] In a pure inductive circuit, current is lagging by 90 degrees from the voltage. The power factor is the cosine of the angle in between the voltage and the current. If the angle between the voltage and current is 90, then cos90=0. Hence, the power factor is zero.

6. If the power factor is 10 and the value of inductive reactance is 20 ohm, calculate the resistance in the circuit.
a) 1 ohm
b) 2 ohm
c) 3 ohm
d) 4 ohm

View Answer

Answer: b [Reason:] We know that: cos(phi)=R/XL From the given question, we find that the resistance in the circuit is 2 ohm.

7. If the resistance in a circuit is 2 ohm and the inductive resistance is 20 ohm, calculate the power factor.
a) 10
b) 20
c) 30
d) 40

View Answer

Answer: a [Reason:] We know that: cos(phi)=R/XL From the given question, we find that the power factor is 10.

8. If the power factor is 10 and the resistance is 2 ohm, calculate the inductive reactance.
a) 10 ohm
b) 20 ohm
c) 30 ohm
d) 40 ohm

View Answer

Answer: b [Reason:] We know that: cos(phi)=R/XL From the given question, we find that the inductive reactance is 20 ohm.

9. 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.

10. An induced emf is said to be ________
a) Inductive
b) Capacitive
c) Resistive
d) Cannot be determined

View Answer

Answer: a [Reason:] Any circuit in which a change of current is accompanied by a change of flux, and therefore by an induced emf, is said to be inductive.

Set 4

1. Find the value of v if v1=20V.
basic-electrical-engineering-questions-answers-kirchhoffs-current-law-q1
a) 10V
b) 12V
c) 14V
d) 16V

View Answer

Answer: b [Reason:] The current through the 10 ohm resistor=v1/10=2A.Applying KCL at node 1: i5=i10+i2. i2=6-2=4A. Thus the drop in the 2 ohm resistor= 4×2=8V. v1=20V; hence v2=20-v across 2 ohm resistor=20-8=12V v2=v since they are connected in parallel. v=12V.

2. Calculate the current A.
basic-electrical-engineering-questions-answers-kirchhoffs-current-law-q2
a) 5A
b) 10A
c) 15A
d) 20A

View Answer

Answer: c [Reason:] KCl states that the total current leaving the junction is equal to the current entering it. In this case, the current entering the junction is 5A+10A=15A.

3. Calculate the current across the 20 ohm resistor.
basic-electrical-engineering-questions-answers-kirchhoffs-current-law-q3
a) 20A
b) 1A
c) 0.67A
d) 0.33A

View Answer

Answer: d [Reason:] Using current divider rule the current through the 20 ohm resistor= (total current in the circuit x resistance of the other branch)/total resistance= 1×10/30=3.33A.

4. Calculate the value of I3, if I1= 2A and I2=3A.
basic-electrical-engineering-questions-answers-kirchhoffs-current-law-q4
a) -5A
b) 5A
c) 1A
d) -1A

View Answer

Answer: a [Reason:] According to KCl, I1+I2+I3=0. Hence I3=-(I1+I2)=-5A.

5. Find the value of i2, i4 and i5 if i1=3A, i3=1A and i6=1A.
basic-electrical-engineering-questions-answers-kirchhoffs-current-law-q5
a) 2,-1,2
b) 4,-2,4
c) 2,1,2
d) 4,2,4

View Answer

Answer: a [Reason:] At junction a: i1-i3-i2=0. i2=2A. At junction b: i4+i2-i6=0. i4=-1A. At junction c: i3-i5+i4=0. i5=2A.

6. What is the value of current if a 50C charge flows in a conductor over a period of 5 seconds?
a) 5A
b) 10A
c) 15A
d) 20A

View Answer

Answer: b [Reason:] Current=Charge/Time. Here charge = 50c and time = 5seconds, so current = 50/5 = 10A.

7. KCL deals with the conservation of?
a) Momentum
b) Mass
c) Potential Energy
d) Charge

View Answer

Answer: d [Reason:] KCL states that the amount of charge entering a junction is equal to the amount of charge leaving it, hence it is the conservation of charge.

8. KCL is applied at _________
a) Loop
b) Node
c) Both loop and node
d) Neither loop nor node

View Answer

Answer: b [Reason:] KCL states that the amount of charge leaving a node is equal to the amount of charge entering it, hence it is applied at nodes.

9. KCL can be applied for __________
a) Planar networks
b) Non-planar networks
c) Both planar and non-planar
d) Neither planar nor non-planar

View Answer

Answer: c [Reason:] KCL is applied for different nodes of a network whether it is planar or non-planar.

10. What is the value of the current I?
basic-electrical-engineering-questions-answers-kirchhoffs-current-law-q10
a) 8A
b) 7A
c) 6A
d) 5A

View Answer

Answer: a [Reason:] At the junction, I-2+3-4-5=0. Hence I=8A.

Set 5

1. Mesh analysis is generally used to determine?
a) Voltage
b) Current
c) Resistance
d) Power

View Answer

Answer: b [Reason:] Mesh analysis uses Kirchhoff’s Voltage Law to find all the mesh currents. Hence it is a method used to determine current.

2. KVL is associated with____________
a) Mesh analysis
b) Nodal analysis
c) Both mesh and nodal
d) Neither mesh nor nodal

View Answer

Answer: a [Reason:] KVL employs mesh analysis to find the different mesh currents by finding the IR products in each mesh.

3. KCL is associated with_________
a) Mesh analysis
b) Nodal analysis
c) Both mesh and nodal
d) Neither mesh nor nodal

View Answer

Answer: b [Reason:] KCL employs nodal analysis to find the different node voltages by finding the value if current in each branch.

4. Nodal analysis is generally used to determine?
a) Voltage
b) Current
c) Resistance
d) Power

View Answer

Answer: a [Reason:] Nodal analysis uses Kirchhoff’s Current Law to find all the node voltages. Hence it is a method used to determine voltage.

5. Find the value of the source current from the following circuit.
basic-electrical-engineering-questions-answers-kirchhoffs-law-network-solution-q5
a) 2.54A
b) 6.67A
c) 3.35A
d) 7.65A

View Answer

Answer: a [Reason:] I3 =(3+j0)A V2 =I3R=(3+j0)(8+j0)=(24+j0)V I2=V2/Xc=(j1.5) A I1 =I2 +I3 =(0+j1.5)+(3+j0)=(3+j1.5)A I1=(32+1.52)1/2= 3.35A.

6. Find the value of the source voltage from the following circuit.
basic-electrical-engineering-questions-answers-kirchhoffs-law-network-solution-q5
a) 49.2V
b) 34.6V
c) 65.2V
d) 25.6V

View Answer

Answer: a [Reason:] I3 =(3+j0)A V2 =I3R=(3+j0)(8+j0)=(24+j0)V I2=V2/Xc=(0 + j1.5) A I1 =I2 +I3 =(0+j1.5)+(3+j0)=(3+j1.5)A I1=(32+1.52)1/2= 3.35A. V1 =I1(R+jXL) =(15+j30)V E=V1 +V2 =(39+j30)V E=(392+302)1/2= 49.2V.

7. According to KVL, the algebraic sums of all the IR products and the voltages in a loop is?
a) Always positive
b) Always negative
c) Always zero
d) Always infinity

View Answer

Answer: c [Reason:] According to KVL, the algebraic sums of all the IR products and the voltages in a closed loop are always equal to zero due to the law of conservation of energy.

8. Kirchhoff’s laws are valid for ___________
a) Linear circuits only
b) Both linear and non-linear circuits
c) Neither linear nor non-linear circuits
d) Both linear and non-linear circuits

View Answer

Answer: d [Reason:] KCL and KVL both are applied for both linear and non linear circuits because they are formulated fro the physical laws of conservation of energy and charge respectively.

9. KCL is based on _____________
a) Law of conservation of energy
b) Law of conservation of charge
c) Both conservation of energy and charge
d) Neither conservation of energy nor charge

View Answer

Answer: b [Reason:] Kirchhoff’s current law is based on the law of conservation of charge. It states that the sum of the currents entering and leaving a junction taken with the correct sign is equal to zero.

10. KVL is based on ___________
a) Law of conservation of energy
b) Law of conservation of charge
c) Both conservation of energy and charge
d) Neither conservation of energy nor charge

View Answer

Answer: b [Reason:] Kirchhoff’s current law is based on the law of conservation of energy. According to KVL, the algebraic sums of all the IR products and the voltages in a closed loop are always equal to zero due to the law.