NCERT Solutions for Class 9 Science Chapter 11

Important NCERT Questions

Work and Energy

NCERT Books for Session 2022-2023

CBSE Board and UP Board

Exercises Questions

Page No-159

Questions No-14

# An electric heater is rated 1500 W. How much energy does it use in 10 hours?

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1. Power Rating of the Electric Heater:

– The power rating of the electric heater is 1500 watts (W).

2. Time Duration:

– The time duration for which we want to calculate the energy used is 10 hours.

3. Formula for Energy Calculation:

– The formula to calculate energy (in joules) is: Energy = Power × Time

4. Conversion of Time:

– Convert the time duration from hours to seconds because the power is given in watts.

– 10 hours = 10 x 60 x 60 seconds = 36,000 seconds

5. Calculation of Energy Used:

– Energy Used = Power × Time

– Energy Used = 1500 W x 36,000 s

– Energy Used = 54,000,000 J

6. Conversion to Kilowatt-Hours (Optional):

– To express energy in kilowatt-hours (kWh), divide the energy in joules by 3.6 x 10⁶ (since 1 kWh = 3.6 x 10⁶ J).

– Energy Used in kWh = (54,000,000 J)/(3.6 x 10⁶ J/kWh)

– Energy Used in kWh = 15 kWh

Therefore, the electric heater rated at 1500 W will consume 54,000,000 joules of energy or 15 kilowatt-hours of energy in 10 hours of operation.