electrical engineering multiple choice questions and answers pdf download objective questions quiz for competitive exams electrical mcqs book.

BASIC ELECTRICAL ENGINEERING MCQs

( BTech 1st Year )

**1-Which of the following motors is used in ceiling fan?**

(A) Universal motor

(B) Synchronous motor

(C) Series motor

(D) Induction motor

Answer: D

**2-Number of parallel path in wave winding is:**

(A) 2

(B) 3

(C) 4

(D) 6

Answer: A

**3-CT is used for measuring**

(A) Voltage

(B) Frequency

(C) Power factor

(D) Alternating current

Answer: D

**4-Active power in 3 phase circuit is:**

(A) √3 VLIL Cosφ

(B) 3 VLIL Cosφ

(C) √2 VLIL Cosφ

(D) 2 VLIL Cosφ

Answer: A

**5-Zener diodes are commonly used as:**

(A) Rectifier

(B) Amplifier

(C) Voltage regulator

(D) Filter

Answer:C

**6-Unit of reluctance:**

(A) Ampere Turns/Weber

(B) Weber Turns

(C) Henry

(D) Weber Turns/Ampere

Answer: A

**7-Unit of luminous intensity is**

(A) Lumen

(B) Lux

(C) Lumen/m2

(D) Candela

Answer: D

**8-Which of the following is secondary cell?**

(A) Dry cell

(B) Leclanche cell

(C) Voltaic cell

(D) Lead acid cell

Answer: D

**9-Energy stored in inductor is:**

(A) W = (1/4)LI2

(B) W = (1/2)LI2

(C) W = (1/2)L2I

(D) W = (1/2)L2I2

Answer: B

**10-The power factor of pure resistive circuit is**

(A) Zero

(B) Leading

(C) Lagging

(D) Unity

Answer: D

**11. Find the current in the circuit.**

a) 1 A

b) 2 A

c) 3 A

d) 4 A

Answer: b

Explanation: I=V/R. Total resistance R = 20+40=60ohm. V=120V. I=120/60=2A.

**12. In a series circuit, which of the parameters remain constant across all circuit elements such as resistor, capacitor and inductor etcetera?**

a) Voltage

b) Current

c) Both voltage and current

d) Neither voltage nor current

Answer: b

Explanation: In a series circuit, the current across all elements remain the same and the total voltage of the circuit is the sum of the voltages across all the elements.

**13. Voltage across the 60ohm resistor is______**

a) 72V

b) 0V

c) 48V

d) 120V

Answer: b

Explanation: The 60ohm resistance is shorted since current always choses the low resistance path. Voltage across short circuit is equal to zero, hence voltage across the resistor is 0.

**14. Find the voltage across the 6 ohm resistor.**

a) 150V

b) 181.6V

c) 27.27V

d) 54.48V

Answer: c

Explanation: Total current I=150/(6+12+15)=(150/33)V.V across 6 ohm = 6*I = 6*(150/33)V = 27.27V.

**15. If there are two bulbs connected in series and one blows out, what happens to the other bulb?**

a) The other bulb continues to glow with the same brightness

b) The other bulb stops glowing

c) The other bulb glows with increased brightness

d) The other bulb also burns out

**16. What is the value of x if the current in the circuit is 5A?**

a) 15 ohm

b) 25 ohm

c) 55 ohm

d) 75 ohm

Answer: a

Explanation: Total voltage=sum of voltages across each resistor.

=>150=10*5+5*5+5*x. Solving the equation, we get x=15 ohm.

**17. A voltage across a series resistor circuit is proportional to?**

a) The amount of time the circuit was on for

b) The value of the resistance itself

c) The value of the other resistances in the circuit

d) The power in the circuit

Answer: b

Explanation: V=IR hence the voltage across a series resistor circuit is proportional to the value of the resistance.

**18. Many resistors connected in series will?**

a) Divide the voltage proportionally among all the resistors

b) Divide the current proportionally

c) Increase the source voltage in proportion to the values of the resistors

d) Reduce the power to zero

Answer: a

Explanation: In a series circuit, the current remains the same across all resistors hence the voltage divides proportionally among all resistors.

**19. What is the voltage measured across a series short?**

a) Infinite

b) Zero

c) The value of the source voltage

d) Null

Answer: b

Explanation: A short is just a wire. The potential difference between two points of a wire is zero hence the voltage measured is equal to zero.

**20. What happens to the current in the series circuit if the resistance is doubled?**

a) It becomes half its original value

b) It becomes double its original value

c) It becomes zero

d) It becomes infinity

Answer: a

Explanation: I=V/R. If R becomes 2R then I becomes I/2 i.e. half of its original value.

**21. 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

Answer: b

Explanation: 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 of the parallel circuit. Hence the other bulb continues to glow. Also the voltage across other bulb remains the same due to which power delivered to it remains the same so it continues to glow with the same brightness.

**22. Calculate the current across the 20 ohm resistor.**

a) 10A

b) 20A

c) 6.67A

d) 36.67A

Answer: a

Explanation: I=V/R. Since in parallel circuit, voltage is same across all resistors. Hence across the 20 ohm resistor, V=200V so I=200/20=10A.

**23. 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

Answer: a

Explanation: In parallel circuits, the current across the circuits vary whereas the voltage remains the same.

**24. 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

Answer: b

Explanation: I=V/R. In a parallel circuit, the voltage across each resistor is equal, hence the value of the current is proportional (inversely) to the value of the resistance.

**25. Calculate the total current in the circuit.**

a) 20 A

b) 10 A

c) 11.43 A

d) 15 A

Answer: c

Explanation: The 1 ohm and 2 ohm resistor are in series which is in parallel to the 3 ohm resistor. The equivalent of these resistances (3/2 ohm) is in series with the 4 ohm and 5 ohm resistor. Total R = 21/2 ohm.

I=V/R=120/(21/2)=240/21=11.43 A.

**26. The voltage across the open circuit is?**

a) 100V

b) Infinity

c) 90V

d) 0V

Answer: a

Explanation: 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.

**27. The voltage across the short is?**

a) 135V

b) Infinity

c) Zero

d) 11.25V

Answer: c

Explanation: The voltage across a short is always equal to zero whether it is connected in series or parallel.

**28. If the current through x ohm resistance in the circuit is 5A, find the value of x.**

a) 27 ohm

b) 5 ohm

c) 12 ohm

d) 135 ohm

Answer: a

Explanation: R=V/I. In this circuit I=5A and V=135V. Therefore, R=135/5=27 ohm.

**29. 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

Answer: d

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

**30. The total resistance between A and B are?**

a) 20 ohm

b) 5 ohm

c) 80 ohm

d) 0 ohm

Answer: b

Explanation: The resistors are connected in parallel, hence the equivalent resistance = 1/(1/20+1/20+1/20+1/20)=5A.

**31. It is preferable to connect bulbs in series or in parallel?**

a) Series

b) Parallel

c) Both series and parallel

d) Neither series nor parallel

Answer: b

Explanation: Bulbs are connected in parallel so that even if one of the bulbs blow out, the others continue to get a current supply.

**32. Calculate the total resistance between the points A and B.**

a) 7 ohm

b) 0 ohm

c) 7.67 ohm

d) 0.48 ohm

Answer: c

Explanation: 1 ohm in parallel with 2 ohm give 2/3 ohm equivalent which is in series with 4 ohm and 3 ohm so total resistance between A and B = 4 + 2/3 + 3 = 23/3 = 7.67 ohm.

**33. Calculate the equivalent resistance between A and B.**

a) 60 ohm

b) 15 ohm

c) 12 ohm

d) 48 ohm

Answer: c

Explanation: 5 ohm and 15 ohm are connected in series to give 20 ohm.10ohm and 20 ohm are connected in series to give 30 ohm. Now both equivalent resistances (20ohm and 30 ohm) are in parallel to give equivalent resistance 20*30/(20+30) = 12 ohm.

**34. Calculate the resistance between A and B.**

a) 3.56 ohm

b) 7 ohm

c) 14.26 ohm

d) 29.69 ohm

Answer: a

Explanation: The 1 ohm, 2 ohm and 3 ohm resistors are connected in parallel. Its equivalent resistance is in series with the 4 ohm resistor and the parallel connection of the 5 ohm and 6 ohm resistor. The equivalent resistance of this combination is 80/11 ohm. This is in parallel with 7 ohm to give equivalent resistance between A and B is 3.56 ohm.

**35. Batteries are generally connected in______**

a) Series

b) Parallel

c) Either series or parallel

d) Neither series nor parallel

Answer: a

Explanation: Batteries are generally connected in series so that we can obtain the desired voltage since voltages add up once they are connected in series.

**36. In a _________ circuit, the total resistance is greater than the largest resistance in the circuit.**

a) Series

b) Parallel

c) Either series or parallel

d) Neither series nor parallel

Answer: a

Explanation: In series circuits, the total resistance is the sum of all the resistance in the circuit, hence the total is greater than the largest resistance.

**37. In a ____________ circuit, the total resistance is smaller than the smallest resistance in the circuit.**

a) Series

b) Parallel

c) Either series or parallel

d) Neither series nor parallel

Answer: b

Explanation: in a parallel circuit, the equivalent resistance=1/sum of the reciprocals of all the resistances in the circuit. Hence it is smaller than the smallest resistance in the circuit.

**38. Which is the most cost efficient connection?**

a) Series

b) Parallel

c) Either series or parallel

d) Neither series nor parallel

Answer: a

Explanation: The advantage of series-connections is that they share the supply voltage, hence cheap low voltage appliances may be used.

**39. Calculate the equivalent resistance between A and B.**

a) 2 ohm

b) 4 ohm

c) 6 ohm

d) 8 ohm

Answer: b

Explanation: R=((2+3)||5)+1.5)||4. The 2 and the 3 ohm resistor are in series. The equivalent of these two resistors is in parallel with the 5 ohm resistor. The equivalent of these three resistances is in series with the 1.5 ohm resistor. Finally, the equivalent of these resistances is in parallel with the 4 ohm resistor.

**40. Calculate the equivalent resistance between A and B.**

a) 6.67 ohm

b) 46.67 ohm

c) 26.67 ohm

d) 10.67 ohm

Answer: a

Explanation: R=20||20||20=6.67 ohm. The three 20 ohm resistors are in parallel and re-sistance is measured across this terminal.

**41. Find the value of v if v1=20V and value of current source is 6A.**

a) 10V

b) 12V

c) 14V

d) 16V

Answer: b

Explanation: 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.

**42. Calculate the current A.**

a) 5A

b) 10A

c) 15A

d) 20A

Answer: c

Explanation: 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.

**43. Calculate the current across the 20 ohm resistor.**

a) 20A

b) 1A

c) 0.67A

d) 0.33A

Answer: d

Explanation: Assume lower terminal of 20 ohm at 0V and upper terminal at V volt and applying KCL, we get V/10 +V/20 =1. V=20/3V So current through 20 ohm

= V/20 = (20/3)/20 =1/3=0.33V.

44. Calculate the value of I3, if I1= 2A and I2=3A.

a) -5A

b) 5A

c) 1A

d) -1A

Answer: a

Explanation: According to KCl, I1+I2+I3=0. Hence I3=-(I1+I2)=-5A.

**45. Find the value of i2, i4 and i5 if i1=3A, i3=1A and i6=1A.**

a) 2,-1,2

b) 4,-2,4

c) 2,1,2

d) 4,2,4

Answer: a

Explanation: 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.

**46. 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

Answer: b

Explanation: Current=Charge/Time. Here charge = 50c and time = 5seconds, so current = 50/5 = 10A.

**47. KCL deals with the conservation of?**

a) Momentum

b) Mass

c) Potential Energy

d) Charge

Answer: d

Explanation: 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.

**48. KCL is applied at _________**

a) Loop

b) Node

c) Both loop and node

d) Neither loop nor node

Answer: b

Explanation: 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.

**49. KCL can be applied for __________**

a) Planar networks

b) Non-planar networks

c) Both planar and non-planar

d) Neither planar nor non-planar

Answer: c

Explanation: KCL is applied for different nodes of a network whether it is planar or non-planar.

**50. What is the value of the current I?**

a) 8A

b) 7A

c) 6A

d) 5A

Answer: a

Explanation: At the junction, I-2+3-4-5=0. Hence I=8A.