This set of Basic Electrical Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Energy”.
1. Which among the following is a unit for electrical energy?
Explanation: Watt is a unit of power and hour is a unit of time. Energy is the product of power and time, hence the unit for power is kWh.
2. A bulb has a power of 200W. What is the energy dissipated by it in 5 minutes?
Explanation: Here, Power = 200w and time = 5min. E=Pt => E= 200*5= 1000Wmin=60000Ws= 60000J= 60kJ.
3. Out of the following, which one is not a source of electrical energy?
a) Solar cell
Explanation: A potentiometer is an instrument used for measuring voltage hence it is not a source for electrical energy.
Explanation: Here V = 100 and R = 10. Power in the circuit= V2/R= 1002/10= 1000W.
Energy= Pt= 1000*50= 50000J= 50kJ.
5. Which among the following is an expression for energy?
Explanation: Expression for power= VI, substituting I from ohm’s law we can write, P=V2/R. Energy is the product of power and time, hence E=Pt= V2t/R.
Explanation: Since the resistors are connected in parallel, the voltage across both the resistors are the same, hence we can use the expression P=V2/R. P=2002/10= 4000W. E=Pt= 4000*10=40000Ws= 40000J= 40kJ.
7. A battery converts___________
a) Electrical energy to chemical energy
b) Chemical energy to electrical energy
c) Mechanical energy to electrical energy
d) Chemical energy to mechanical energy
Explanation: A battery is a device in which the chemical elements within the battery react with each other to produce electrical energy.
8. A current of 2A flows in a wire offering a resistance of 10ohm. Calculate the energy dissipated by the wire in 0.5 hours.
Explanation: Here I (current) = 2A and Resistance(R) = 10ohm. Power= I2R= 22*10=40. Energy=Pt= 40*0.5*60*60= 72000J=72kJ.
Explanation: The current in the circuit is equal to the current in the 5 ohm resistor since it a series connected circuit, hence I=220/(5+10)=14.67A. P=I2R= 14.672*5=1075.8W. E=Pt= 1075.8*20= 21516J=21.5kJ.
10. Practically, if 10kJ of energy is supplied to a device, how much energy will the device give back?
a) Equal to10kJ
b) Less than 10kJ
c) More than 10kJ
Explanation: Practically, if 10kJ of energy is supplied to a system, it returns less than the supplied energy because, some of the energy is lost as heat energy, sound energy etc.
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.