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Q91
(NDA-II/2011)
Science & Technology › Basic Science (Physics, Chemistry, Biology) › Electricity and magnetism
Answer Verified
An electric lamp of 100 watt is used for 10 hours per day. The ‘units’ of energy consumed in one day by the lamp is
Result
Your answer:
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Correct:
A
Explanation
The energy consumed by an electrical appliance is calculated by multiplying its power rating by the time it is used. In this case, the electric lamp has a power of 100 watts (W) and is used for 10 hours (h) per day. The total energy consumed in one day is 100 W × 10 h = 1,000 watt-hours (Wh) [t3]. The commercial unit of electrical energy is the kilowatt-hour (kWh), which is commonly referred to as a 'unit' [c1][c2]. Since 1 kilowatt (kW) equals 1,000 watts, 1,000 Wh is equivalent to 1 kWh (1,000 Wh / 1,000 = 1 kWh) [t2][t7]. Therefore, a 100-watt lamp operating for 10 hours consumes exactly 1 unit of electricity [t2][t6]. This standard conversion is fundamental for utility billing and energy management [t1].
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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