Question

Ten identical electric bulbs, each rated $220V$, $50W$ are used in parallel on $220V$ line for $10$ hours per day in a month of $30$ days. The electric energy consumed in kilo watt hours is

• A. $1500$
• B. $15,000$
• C. $15$
• D. $150$

Answer 1

The correct option is D $150$

Answer is D.
The SI unit of electric power is watt (W).
$1W=1volt\times 1ampere=1V\times 1A$
1 kilo watt or $1kW=1000W$
In this case, the power of the bulb is given as $50W$

.
So, kilo-watt rating of each bulb is given as $\frac{50}{1000}kW$

kilo-watt rating of all 10 bulbs is $=\frac{50}{1000}kW\times 10=0.5kW$.

Total number of units in kWh consumed in one day $=0.5kW\times 10hours=5units/day.$
Therefore, the total electrical energy in a month, that is, 30 days $=5\times 30=150units$.
Hence, the electric energy consumed in kilo watt hours is 150 kWh.