Basic Electrical Engineering Questions and Answers – Power

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This set of Basic Electrical Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Power”.

1. Which of the following is not an expression power?
a) P=VI
b) P=I2R
c) P=V2/R
d) P=I/R
View Answer

Answer d
Explanation: Power is the product of voltage and current. Writing I in terms of V, we get P=V2/R and writing V in terms of I, we get P=I2r.
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2. Which of the following statements are true?
a) Power is proportional to voltage only
b) Power is proportional to current only
c) Power is neither proportional to voltage nor to the current
d) Power is proportional to both the voltage and current
View Answer

Answer: d
Explanation: Power is proportional to both voltage and current.

3. A 250V bulb passes a current of 0.3A. Calculate the power in the lamp.
a) 75W
b) 50W
c) 25W
d) 90W
View Answer

Answer: a
Explanation: Here, V = 250v and I = 0.3A. P=VI. Which implies that, P=250*0.3=75W.
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4. Kilowatt-hour(kWh) is a unit of?
a) Current
b) Power
c) Energy
d) Resistance
View Answer

Answer: c
Explanation: Power is the energy per unit time. That is, P=E/t. If the unit of power in kW and the unit of time is an hour, then the unit of energy=unit of power*unit of time=kWh.

5. Calculate the power in the 20 ohm resistance.
Find the power in the 20 ohm resistance
a) 2000kW
b) 2kW
c) 200kW
d) 2W
View Answer

Answer: b
Explanation: Here V = 200v and Resistance( R) = 20ohm. P=V2/R= 2002/20=2000W=2kW.
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6. A current of 5A flows in a resistor of 2 ohms. Calculate the energy dissipated in 300 seconds in the resistor.
a) 15kJ
b) 15000kJ
c) 1500J
d) 15J
View Answer

Answer: a
Explanation: P=I2R =52*2=50W.
E= Pt=50*300=15000J=15kJ.

7. Calculate the power across each 20 ohm resistance.
Find the Power across each 20 ohm resistance if current in resistance is same
a) 1000W, 1000W
b) 500W, 500W
c) 1000kW, 1000kW
d) 500kW, 500kW
View Answer

Answer: b
Explanation: This is a series connected circuit hence the current across each resistance is the same. To find current: I=V/R=200/20=5A.
To find power: P=I2R=52*20=500W. Since both the resistors have a resistance of 20 ohms, the power across both is the same.
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8. Calculate the power across each 10 ohm resistance.
Find the power across each 10 ohm resistance in given parallel connected circuit
a) 1000kW, 1000kW
b) 1kW, 1kW
c) 100W, 100W
d) 100kW, 100kW
View Answer

Answer: b
Explanation: This is parallel connected circuit, hence the voltage across each of the resistors is the same. P =(V2)/R=(1002)/10 = 1000W=1kW. Since both the resistors receive the same amount of voltage, the power in both is the same.

9. Calculate the work done in a resistor of 20 ohm carrying 5A of current in 3 hours.
a) 1.5J
b) 15J
c) 1.5kWh
d) 15kWh
View Answer

Answer: c
Explanation: To find power: P=I2R=52*20=500W=0.5kW.
To find Work done: W=Pt=0.5*3=1.5kWh.
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10. The SI unit of power is?
a) kW(kilo-watt)
b) J/s(joules per second)
c) Ws(watt-second)
d) J/h(joules per hour
View Answer

Answer: b
Explanation: Power = energy/time
SI unit of power = SI unit of energy/SI unit of time = joule/second.

Sanfoundry Global Education & Learning Series – Basic Electrical Engineering.

To practice all areas of Basic Electrical Engineering, here is complete set of 1000+ Multiple Choice Questions and Answers.

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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