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Q9
(CDS-II/2019)
Science & Technology › Basic Science (Physics, Chemistry, Biology) › Electricity and magnetism
Answer Verified
A 100 W electric bulb is used for 10 hours a day. How many units of energy are consumed in 30 days ?
Result
Your answer:
—
·
Correct:
C
Explanation
To calculate the energy consumed, we use the formula: Energy (kWh) = (Power in Watts × Time in hours) / 1000. The commercial unit of electrical energy is the kilowatt-hour (kWh), commonly referred to as a 'unit' [2]. For a 100 W bulb used for 10 hours a day, the daily consumption is (100 W × 10 h) / 1000 = 1 kWh per day. Over a period of 30 days, the total energy consumed is 1 kWh/day × 30 days = 30 kWh. Since 1 kWh is equivalent to 1 unit, the total energy consumed in 30 days is 30 units. This calculation follows the standard relationship where energy is the product of power and time, scaled to the kilowatt-hour for commercial billing purposes [1].
Sources
- [1] Science , class X (NCERT 2025 ed.) > Chapter 11: Electricity > 11.8 ELECTRIC POWER > p. 191
- [2] Science , class X (NCERT 2025 ed.) > Chapter 11: Electricity > What you have learnt > p. 192
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