What is a kilowatt-hour? How many Joules in 1 kWh?
The correct answer and explanation is :
A kilowatt-hour (kWh) is a unit of energy commonly used to measure electricity consumption. It represents the amount of energy consumed when a device with a power rating of 1 kilowatt (kW) operates for 1 hour.
✅ Correct Answer:
1 kilowatt-hour = 3,600,000 joules (J)
or
1 kWh = 3.6 × 10⁶ J
📘 Detailed Explanation (300+ words):
To understand what a kilowatt-hour is, it’s important to break down the terms:
- Watt (W) is the unit of power, defined as 1 joule per second (1 W = 1 J/s).
- Kilowatt (kW) is 1,000 watts, so 1 kW = 1,000 J/s.
- When you multiply power (in watts) by time (in seconds), you get energy (in joules).
A kilowatt-hour measures the total amount of energy used over time, not just the rate at which it’s used.
Let’s do the math:
[
1 \text{ kilowatt-hour} = 1 \text{ kW} × 1 \text{ hour}
= 1,000 \text{ watts} × 3,600 \text{ seconds}
= 1,000 \text{ J/s} × 3,600 \text{ s}
= 3,600,000 \text{ J}
= 3.6 × 10^6 \text{ J}
]
This means 1 kWh is equivalent to using 1,000 watts of power continuously for 1 hour, which results in the consumption of 3.6 million joules of energy.
🔌 Practical Example:
Suppose you have a 100-watt light bulb:
- If it runs for 10 hours, it will consume:
[
100 \text{ watts} × 10 \text{ hours} = 1,000 watt-hours = 1 kWh
]
So, even small appliances, over time, can use a full kilowatt-hour of energy.
⚡ In the Real World:
Utility companies use kilowatt-hours to charge consumers. For example, if electricity costs $0.15 per kWh, running a 1,000-watt heater for 1 hour costs 15 cents.
In summary, a kilowatt-hour is a convenient and practical way to measure energy usage over time, and it is equal to 3.6 million joules.