Question

One kilowatt hour is equal to

• A. $36 \times 10^{-5}\, J$
• B. $36 \times 10^{-4}\, J$
• C. $36 \times 10^5\, J$
• D. $36 \times 10^3\, J$

Answer 1

The Correct Option is C

To solve the problem of determining what one kilowatt hour (kWh) is equivalent to in joules, we need to understand the relationship between these units.

1. A kilowatt hour is a unit of energy. It represents the amount of energy consumed when a 1-kilowatt (kW) device runs for 1 hour.

2. The relationship between kilowatts, watts, and joules is as follows: 1 kW = 1000 watts and 1 watt = 1 joule per second.

3. Therefore, 1 kWh is equal to the energy of a 1000-watt device operating for 3600 seconds (since there are 3600 seconds in an hour).

Calculating this, we have:

1 \, \text{kWh} = 1000 \, \text{W} \times 3600 \, \text{s} = 3600000 \, \text{J}

4. Converting this to scientific notation, we get:

3600000 \, \text{J} = 3.6 \times 10^6 \, \text{J}

5. Now let's compare this with the given options:

• 36 \times 10^{-5}\, J: This value is incorrect as it is significantly smaller than the energy in one kWh.
• 36 \times 10^{-4}\, J: This value is also incorrect for the same reason above.
• 36 \times 10^5\, J: This option is the correct answer when simplified aligns with our calculation of 3.6 \times 10^6 \, \text{J}.
• 36 \times 10^3\, J: This value is incorrect as it is much smaller than the calculated value.

Hence, the correct answer is 36 \times 10^5 \, \text{J}, which aligns with the scientific notation format of the calculated value of one kilowatt hour.