Final answer:
Power companies measure electric power consumption in kilowatt-hours (kWh), a convenient unit that represents the product of power in kilowatts and time in hours, and is equivalent to 3.6 million joules, or 3.6 MJ.
Step-by-step explanation:
Power companies describe watt usage in kilowatt-hours (kWh), which is an energy unit used to measure the consumption of electric power over time. The choice of kilowatt-hours as a unit is convenient for both power companies and customers because it directly relates to how electricity is typically used in households and businesses - consumed over extended periods at a rate of kilowatts. To provide more perspective, one kilowatt-hour is equivalent to an energy consumption of one kilowatt sustained over one hour and can be converted into 3.6 million joules, or 3.6 MJ.
The relationship between kilowatt-hours and joules is essential in understanding why power companies prefer the former unit for billing purposes. The SI unit for energy, the joule, is much smaller than the kilowatt-hour, making it impractical for large-scale billing due to the enormous numbers that would be involved. Therefore, expressing energy use in kilowatt-hours is far more practical and easier for consumers to understand, facilitating a clearer comprehension of their energy usage and related costs.