Question

Which of the following is the commercial unit of electrical energy?

• A. watt/hour
• B. unit
• C. watt
• D. none of these

Hint:

Electricity bills are calculated in units, where 1 unit = 1 kilowatt-hour.

Answer 1

The Correct Option is B

Step 1: Basic Unit of Electrical Energy:
The SI unit of electrical energy is the joule (J). \[ 1 \, \text{joule} = 1 \, \text{watt} \times 1 \, \text{second} \] Step 2: Commercial Unit:
In practice, energy consumed in households and industries is very large. So, the commercial unit is taken as: \[ 1 \, \text{unit} = 1 \, \text{kWh} = 1000 \, \text{watt} \times 3600 \, \text{seconds} = 3.6 \times 10^6 \, \text{joules} \] Step 3: Analysis of Options:
watt/hour → rate, not energy.
watt → unit of power, not energy.
unit → correct commercial unit.
Step 4: Final Answer:
The commercial unit of electrical energy is unit (kWh).