Energy–Power–Time Relationship in Electrical Engineering Evaluate the statement: “Energy equals power multiplied by time.”

Introduction / Context:
The relationship among energy, power, and time is fundamental to all of engineering. It underlies billing for electricity (kWh), battery sizing, and performance evaluation of machines and systems. This item verifies command of the basic definition linking these quantities.

Given Data / Assumptions:

• Power P is the rate of doing work or transferring energy.
• Energy W is the accumulated work over a time interval.
• Time t is measured in seconds (or hours for practical billing).

Concept / Approach:

By definition, power is the time rate of change of energy: P = dW/dt. Integrating both sides over time gives W = ∫ P dt. For constant power, this reduces to W = P * t. Units confirm: watt * second = joule; kilowatt * hour is a common energy billing unit.

Step-by-Step Solution:

Verification / Alternative check:

Check units: watt (J/s) times second gives joule. For practical metering, 1 kWh = 1000 W * 3600 s = 3.6 × 10^6 J, consistent with the definition.

Why Other Options Are Wrong:

Limiting the result to DC or resistive loads is unnecessary; the definition holds generally. “Energy equals voltage multiplied by time” has wrong dimensions; volts * seconds is not energy.

Common Pitfalls:

Confusing instantaneous power with average power in time-varying scenarios; always integrate P(t) for accurate energy over the interval.

Final Answer:

True