How much power is delivered by a voltage of 13.8 volts DC and a current of 10 amperes?
The correct answer is A: 138 watts. With a voltage of 13.8 volts DC and a current of 10 amperes, the power delivered is 138 watts. Using the power formula P = I × E: P = 10 A × 13.8 V = 138 watts.
This is a straightforward application of the power formula. 13.8 volts is the standard voltage for mobile amateur radio equipment (typical vehicle electrical system voltage when the engine is running). A 10-ampere current draw is common for a 50-watt transceiver operating at full power. The 138 watts represents the input power to the transceiver (output power would be less due to efficiency losses).
Exam Tip
Power = Current × Voltage. Remember: P = I × E. 10 A × 13.8 V = 138 W. This is a common calculation for mobile equipment.
Memory Aid
"**1**3.**8**V × **1**0A = **1**38W (think '13.8 × 10 = 138')"
Real-World Application
Your mobile transceiver operates from your vehicle's 13.8-volt electrical system and draws 10 amperes when transmitting at full power. The power consumed is 10 × 13.8 = 138 watts. This tells you how much power your transceiver is using, which helps you understand power supply requirements and battery drain.
FCC Part 97.313Key Concepts
Why Other Options Are Wrong
Option B: Incorrect. 0.7 watts would be the result of dividing voltage by current (13.8 / 10 = 1.38), not multiplying. Power is I × E, not E / I.
Option C: Incorrect. 23.8 watts would be the result of subtracting (13.8 - 10 = 3.8) or some other incorrect calculation. Power is I × E.
Option D: Incorrect. 3.8 watts would be the result of subtracting (13.8 - 10 = 3.8), not the correct power calculation.
题目解析
The correct answer is A: 138 watts. With a voltage of 13.8 volts DC and a current of 10 amperes, the power delivered is 138 watts. Using the power formula P = I × E: P = 10 A × 13.8 V = 138 watts. This is a straightforward application of the power formula. 13.8 volts is the standard voltage for mobile amateur radio equipment (typical vehicle electrical system voltage when the engine is running). A 10-ampere current draw is common for a 50-watt transceiver operating at full power. The 138 watts represents the input power to the transceiver (output power would be less due to efficiency losses).
考试技巧
Power = Current × Voltage. Remember: P = I × E. 10 A × 13.8 V = 138 W. This is a common calculation for mobile equipment.
记忆口诀
**1**3.**8**V × **1**0A = **1**38W (think '13.8 × 10 = 138')
实际应用示例
Your mobile transceiver operates from your vehicle's 13.8-volt electrical system and draws 10 amperes when transmitting at full power. The power consumed is 10 × 13.8 = 138 watts. This tells you how much power your transceiver is using, which helps you understand power supply requirements and battery drain.
错误选项分析
Option B: Incorrect. 0.7 watts would be the result of dividing voltage by current (13.8 / 10 = 1.38), not multiplying. Power is I × E, not E / I. Option C: Incorrect. 23.8 watts would be the result of subtracting (13.8 - 10 = 3.8) or some other incorrect calculation. Power is I × E. Option D: Incorrect. 3.8 watts would be the result of subtracting (13.8 - 10 = 3.8), not the correct power calculation.
知识点
Power calculation, P = I × E, DC power, Electrical calculations
Verified Content
Question from official FCC Technician Class question pool. Explanation reviewed by licensed amateur radio operators.