Test: Power Energy - Electrical Engineering (EE) MCQ

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.

Power is proportional to both voltage and current. Hence both the options are right.

Here, V = 250v and I = 0.3A. P=VI. Which implies that, P=250*0.3=75W.

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

Here V = 200v and Resistance( R) = 20ohm. P=V²/R= 200²/20=2000W=2kW

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

This is a series connected circuit hence the current across each resistance is the same. To find current: I=V/R=200/40=5A.
To find power: P=I²R=(5)²*20 = 500W. Since both the resistors have a resistance of 20 ohm, the power across both is the same.

This parallel connected circuit, hence the voltage across each of the resistors are the same. P=V2/R= 1002/10=1000W=1kW. Since both the resistors receive the same amount of voltage, the Power in both are the same.

To find power: P=I²R=5²*20=500W=0.5kW.
To find Work done: W=Pt=0.5*3=1.5kWh.

Power = energy/time =J/s(joules per second). Hence the Si unit of Power is J/s.

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.

Here, Power = 200w and time = 5min. E=Pt => E= 200*5= 1000Wmin=60000Ws= 60000J= 60kJ.

 A potentiometer is an instrument used for measuring voltage hence it is not a source for electrical energy.

Here V = 100 and R = 10. Power in the circuit= V²/R= 100²/10= 1000W.
Energy= Pt= 1000*50= 50000J= 50kJ.

 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.

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.

A battery is a device in which the chemical elements within the battery react with each other to produce electrical energy.

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

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.

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.