Final answer:
The power an electric device requires is indicated by its power rating, which is the product of the current flowing through it and the voltage across it, represented by the expression P = IV. The power rating does not depend on the duration the device is on, but rather on the energy consumption rate when it is in use. A kilowatt-hour (kWh) on an electric bill represents the energy consumed.
Step-by-step explanation:
Understanding Electric Power
How much power an electric device requires is indicated by its power rating. Power in an electric circuit is proportional to the product of the current and the voltage. Specifically, the expression for electric power (P) is P = IV, where I is the current in amperes and V is the voltage across the device in volts.
Considering a comparison between a 25-W and a 60-W light bulb, both operating on the same voltage, the 60-W bulb draws more current and therefore has a lower resistance than the 25-W bulb. If the voltage were to be increased, the power consumption would also increase, potentially leading to the bulb burning out quickly if it receives voltage above its design specification.
Electric power is not dependent on how long the appliance is on. A wattage rating indicates the power consumption of an appliance when it is in the 'on' state. Using multiple devices' power ratings, one can estimate the energy consumed and understand the implications of power usage, as in the example of the total wattage used in the restrooms of a school. It's important to understand that power is the rate at which energy is used; therefore, a kilowatt-hour (kWh) on an electric bill represents the amount of energy bought, not the charge, current, voltage, or power alone.