# Basic Electrical Engineering Questions and Answers – Energy

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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?
a) V(volt)
b) kWh(kilowatt-hour)
c) Ohm
d) C(coloumb)

Explanation: Kilowatt is a unit of power and hour is a unit of time. Energy is the product of power and time, hence the unit for Energy is kWh.

2. A bulb has a power of 200W. What is the energy dissipated by it in 5 minutes?
a) 60J
b) 1000J
c) 60kJ
d) 1kJ

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
b) Battery
c) Potentiometer
d) Generator

Explanation: Solar cell converts light energy to electrical energy. Battery converts chemical energy to electrical energy. Generator generates electrical energy using electromagnetic induction. A potentiometer is an instrument used for measuring voltage and consumes electrical energy instead of generating it.
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4. Calculate the energy dissipated by the circuit in 50 seconds. a) 50kJ
b) 50J
c) 100j
d) 100kJ

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?
a) V2It
b) V2Rt
c) V2t/R
d) V2t2/R

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.

6. Calculate the energy in the 10 ohm resistance in 10 seconds. a) 400J
b) 40kJ
c) 4000J
d) 4kJ

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.
a) 72Wh
b) 72kJ
c) 7200J
d) 72kJh

Explanation: Here I (current) = 2A and Resistance(R) = 10ohm. Power = I2R = 22*10=40. Energy = Pt = 40*0.5*60*60 = 72000J=72kJ.

9. Calculate the energy in the 5 ohm resistor in 20 seconds. a) 21.5kJ
b) 2.15kJ
c) 2.15J
d) 21.5J

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
d) Zero

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.

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