Question T5C10
From subelement T5 - T5C
How much power is delivered by a voltage of 12 volts DC and a current of 2.5 amperes?
Why is this correct?
The correct answer is B (30 watts) because power equals voltage times current: P = E × I. With 12 volts and 2.5 amperes: P = 12 V × 2.5 A = 30 W. The other answers result from calculation errors: choice A divides instead of multiplying, choice C adds the values, and choice D uses an incorrect formula entirely.
Memory tip
Power calculations always multiply voltage and current — never divide, add, or subtract them. When you see power questions, immediately identify the two known values and apply P = E × I. The units help verify: volts × amperes always equals watts.
Learn more
In DC circuits, power represents the rate of energy consumption or generation, measured in watts. This fundamental relationship P = E × I applies to all DC amateur radio equipment — from calculating battery drain in portable operations to determining transmitter power consumption. Understanding power calculations helps you select appropriate power supplies, calculate operating time on battery power, and ensure your station operates within safe limits for both equipment protection and regulatory compliance.
Think about it
Why do you think power increases proportionally with both voltage and current, rather than following some other mathematical relationship?