Electrical Energy And Cost
An electric geyser rated 2 kW is used for 1.5 hours each day. How much electrical energy in kilowatt-hours does it consume over a 30-day month?
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About This Question
- Subject
- physics
- Chapter
- current electricity
- Topic
- electrical energy and cost
- Difficulty
- Easy
- Year
- 2025
Solution
Correct Answer:
90 kWh
Electrical energy consumed by an appliance is the product of its power rating and the time of operation, (E = P \times t), and the commercial unit kilowatt-hour corresponds to a power of one kilowatt sustained for one hour. Daily consumption is therefore (E_{day} = 2,\text{kW} \times 1.5,\text{h} = 3) kWh. Over 30 days the total becomes (E = 3 \times 30 = 90) kWh. The value 60 kWh wrongly uses 1 hour per day instead of 1.5 hours. The value 45 kWh halves the power, treating it as 1 kW. The value 120 kWh overstates the daily usage as 4 kWh. This applies the NCERT definition of the kilowatt-hour as the practical unit of electrical energy. A plausibility check confirms the figure: a 2 kW heater running ninety hours total in a month (1.5 hours times 30 days) must consume (2 \times 45 = 90) kWh, consistent with the stepwise result and with typical household billing magnitudes.
This easy difficulty physics question is from the chapter current electricity, covering the topic of electrical energy and cost. It appeared in the 2025 exam.
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