(a)

Define electric power and state its SI unit. The commercial unit of electrical energy is known as 'unit'. Write the relation between this 'unit' and joule.

(b)

In a house, $\displaystyle 2$ bulbs of $\displaystyle 50$ W each are used for $\displaystyle 6$ hours daily and an electric geyser of $\displaystyle 1$ kW is used for $\displaystyle 1$ hour daily. Calculate the total energy consumed in a month of $\displaystyle 30$ days and its cost at the rate of ₹ $\displaystyle 8.00$ per kWh.

Electrical energy, \(\displaystyle \mathrm{E}_{1}\), consumed by $\displaystyle 2$ bulbs of $\displaystyle 50$ W each is \[E_{1}=50 \times 2 \times 6=600 \mathrm{~Wh} \] Electrical energy, \(\displaystyle \mathrm{E}_{2}\), consumed by electric geyser of $\displaystyle 1$ kW is \[E_{2}=1000 \times 1=1000 \mathrm{~Wh} \] Total energy consumed in the month of $\displaystyle 30$ days \[\begin{aligned} {\left[\mathrm{E}_{1}+\mathrm{E}_{2}\right] \times 30 } & =[600+1000] \times 30 \mathrm{~Wh} \\ & =1600 \times 30=48000 \mathrm{~Wh} \\ & =48 \mathrm{kWh} \end{aligned} \] Cost of using these electrical devices at the rate of ₹ $\displaystyle 8.00$ per kwh is \(\displaystyle ₹ 48 \times 8=₹ 384\)