electricity note

1. This is 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.
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.
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.

2. 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=I2
R =52
*2=50W.
E= Pt=50*300=15000J=15kJ.

3. 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

4. b)15J
c)1.5kWh
d)15kWh
View Answer
Answer:c
Explanation:Tofindpower:P=I2
R=52
*20=500W=0.5kW.
To find Work done: W=Pt=0.5*3=1.5kWh.
10.TheSIunitofpoweris?
a)kW(kilo-watt)
b)J/s(joulespersecond)
c)Ws(watt-second)
d)J/h(joulesperhour
View Answer
Answer:b
Explanation:Power=energy/time
SI unit of power = SI unit of energy/SI unit of time = joule/second.
1. The resistance of pure metals ___________
a) Increases with an increase in temperature
b) Decreases with an increase in temperature
c) Remains the same with an increase in temperature
d) Becomes zero with an increase in temperature
View Answer
Answer: a
Explanation: In a conductor, the valence band and conduction band overlap each other,
there is an excess of electrons in the conduction band. When the temperature increases,
there is an overcrowding of electrons in the conduction band hence reducing the mobility
and hence resistance increases
Theresistanceofinsulators __________
a) Increases with an increase in temperature
b) Decreases with an increase in temperature
c) Remains the same with an increase in temperature
d) Becomes zero with an increase in temperature
View Answer
Answer: b
Explanation: In the case of an insulator, the energy gap between the conduction band
and the valence band is very large. When the temperature is increased, the electrons
move from the conduction band to the valence band and hence it starts conducting.
When conductance increases, resistance decreases, since C=1/R. Thus, when the
temperature increases, resistance decreases in insulators.
3. Which of the following statements are true about metals?
a) Metals have a positive temperature coefficient
b) Metals have a negative temperature coefficient
c) Metals have zero temperature coefficient
d) Metals have infinite temperature coefficient
View Answer
Answer: a
Explanation: The resistance of metals increases with an increase in temperature thus, it
has a positive temperature coefficient.

5. 8. The rise or fall in resistance with the rise in temperature depends on ________
a) The property of the conductor material
b) The current in the metal
c) Property of material as well current in that material
d) Does not depend on any factor
View Answer
Answer:
a
Explanation: The rise or fall in resistance with a rise in temperature depends upon the
property of the material. Hence it rises with temperature in metals and falls with
temperature in insulators and semi-conductors