What is electric energy? What is its commercial (or practical) unit? Define it.
✓
Answer
"Electric energy is the amount of energy consumed in an electric circuit in a given time $t$." $\rightarrow$ The energy consumed not only depends upon the electric power of the appliance but also upon the time for which the power is maintained. $\rightarrow$ If a power $P$ (watt) is maintained for time $t$ (second), then the work done or electric energy consumed is $\left.\begin{array}{l}W(\text { joule })=P(\text { watt }) \times t(\text { second }) \\ \text { OR } \\ \text { Electrical energy } W \\ =\text { Electric, power } P \times \text { time } t\end{array}\right\}.......(11.21)$ $\rightarrow$ But the unit 'watt' is very small. Therefore in actual practice we use a much larger unit called 'kilowatt' which is equal to 1000 watt. $\rightarrow$ Since electrical energy is the product of power and time, the unit of electric energy is, therefore, watt hour (Wh). "One watt hour is the energy consumed when 1 watt power is used for 1 hour." $\rightarrow$ The commercial (or practical) unit of electric energy is kilowatt hour (kWh), commonly known as 'unit'.$ \begin{aligned} 1 kWh & =1 \text { kilowatt } \times 1 \text { hour } \\ & =1000 \text { watt } \times 3600 \text { second } \\ & =3.6 \times 10^6 \text { watt second } \\ & =3.6 \times 10^6 \text { joule }(J) \end{aligned} $ Note : The unit kWh is equal to the electric energy consumed, when electric power of 1 kW is consumed for 1 hour. [If 10 electric bulbs, each of rating 100 W are used for 1 hour, then 1 unit of electric energy is consumed.]
Need a full question paper?
Generate a complete, print-ready paper with questions like this in minutes — across 16+ boards, with answer keys.