In electrical science, electric power (the rate of doing electrical work) is measured in which unit?

Introduction / Context:
Electric power describes how quickly electrical energy is converted into other forms such as light, heat or mechanical work. It is a key quantity for rating devices like bulbs, motors and appliances. This question asks for the standard unit used to measure electric power in the International System of Units (SI).

Given Data / Assumptions:

• Power is defined as the rate at which work is done or energy is transferred.
• Electric power in a circuit can be calculated as P = V * I, where V is voltage and I is current.
• We are using SI units for all quantities.
• Volt, joule and ampere are standard SI units for other electrical or energy related quantities.

Concept / Approach:
The SI unit of power is the watt, named after James Watt. One watt equals one joule of energy per second. In electrical circuits, when one volt of potential difference causes a current of one ampere to flow, the power is one watt. Voltage is measured in volts, current in amperes and energy in joules, so none of these alone are power units. The correct answer must be the watt, which directly measures the rate of energy conversion.

Step-by-Step Solution:
Step 1: Recall the basic physics definition of power: P = Work / time, with the SI unit joule per second. Step 2: In electricity, we also use P = V * I, where V is in volts and I is in amperes. Step 3: The derived unit of power is one joule per second, which is assigned the special name watt (symbol W). Step 4: Recognise that volt is the unit of electric potential difference, joule is the unit of energy and ampere is the unit of current, not power. Step 5: Therefore, electric power is measured in watts.

Verification / Alternative check:
Everyday examples confirm this: light bulbs are rated, for example, at 9 W, 40 W or 100 W, and electric appliances often show ratings like 1000 W (1 kilowatt). Electricity bills are based on kilowatt hours, meaning kilowatts of power used over time. You never see volts or amperes used directly as the unit for power, although these quantities help calculate power. Textbooks and device labels consistently use watts and kilowatts for power ratings.

Why Other Options Are Wrong:
Volt: This is the SI unit of electric potential difference (voltage), not power.

Joule: This is the SI unit of energy or work itself, not the rate at which energy is used.
Ampere: This is the SI unit of electric current, the flow of charge per second, not power.

Common Pitfalls:
Because P = V * I, some students mistakenly think volt or ampere might be units of power. Others confuse watt with watt hour, which is a unit of energy, not power. A simple rule is: power is always in watts (or kilowatts), energy is in joules or watt hours, voltage in volts and current in amperes. Keeping these distinctions clear helps in solving many electrical problems correctly.

Final Answer:
Electric power is measured in Watt.