Question

SI unit of electrical energy is
A. Joule
B. Kilowatt hour
C. Kilojoule
D. Watt hour

Answer 1

Hint: Electrical power is also defined as the electric energy consumed per unit time.
P=VI is the equation of electric power. By substituting electric current in this equation, we can find the SI unit of electric energy.

Complete step by step answer:
In a circuit, current flows with respect to the potential difference across it. Which can be written as

$V={\displaystyle \frac{\text{ work done }}{Q}}$ or W=QV

But we know, current is the flow of charges per unit time. i.e.,

$I={\displaystyle \frac{Q}{t}}$ or Q=It

By substituting ‘Q’ in the work done formula, we get
W=V×I×t
From ohm’s law, we know
 V=IR
Now, lets substitute ‘V’ in the work done formula

$E=I^{2}Rt$
$E={\displaystyle \frac{V^2}{R}}t$

The work done notation ‘W’ is replaced by ‘E’ because work done is the energy dissipated. It can be measured in joules and can also be expressed as energy ‘E’. If the voltage is one volt, the current is one ampere and the time is equal to one second, then the electrical energy is equal to one joule. The SI unit of electrical energy is joule (J). It was named after James Prescott Joule.

1 joule can also be defined as the work done when a force of 1 newton (N) moves a body through a distance of 1 meter (m).

 $1J=1kg{\left({\displaystyle \frac{m}{s}}\right)}^2$
So, the correct answer for the given question is option (A).

Note: It is possible to get confused between power and energy. Power is the rate of energy consumed and its SI unit is watt. Whereas, energy is the ability to do work. The power units can also be converted into energy by multiplying it with seconds and hours.