How much current is required to deliver 120 watts at a voltage of 12 volts DC?
The correct answer is B: 10 amperes. To deliver 120 watts at a voltage of 12 volts DC, you need 10 amperes of current. Using the power formula P = I × E and rearranging to solve for current: I = P / E = 120 W / 12 V = 10 amperes.
This is a rearrangement of the power formula. When you know power and voltage, you can calculate current by dividing power by voltage. This is useful for sizing power supplies, fuses, and wiring - if you need 120 watts at 12 volts, you need a power supply and wiring that can handle at least 10 amperes.
Exam Tip
Current = Power / Voltage. Remember: I = P / E. 120 W / 12 V = 10 A. Divide power by voltage to get current.
Memory Aid
"**I** = **P** / **E** (think 'I = P/E' = Current = Power divided by Voltage, 120/12 = 10)"
Real-World Application
You need to power a 120-watt amplifier from a 12-volt battery. To calculate the current required: I = 120 W / 12 V = 10 amperes. This tells you the battery and wiring must be able to supply at least 10 amperes. You'd need a 12-volt battery rated for at least 10 amperes and wiring capable of handling 10 amperes safely.
FCC Part 97.313Key Concepts
Why Other Options Are Wrong
Option A: Incorrect. 0.1 amperes would be the result of dividing voltage by power (12 / 120 = 0.1), not power by voltage. Current = P / E, not E / P.
Option C: Incorrect. 12 amperes would be the result of using voltage as current, which doesn't make sense. Current = P / E = 120 / 12 = 10 A.
Option D: Incorrect. 132 amperes would be the result of adding (120 + 12 = 132), not the correct calculation.
题目解析
The correct answer is B: 10 amperes. To deliver 120 watts at a voltage of 12 volts DC, you need 10 amperes of current. Using the power formula P = I × E and rearranging to solve for current: I = P / E = 120 W / 12 V = 10 amperes. This is a rearrangement of the power formula. When you know power and voltage, you can calculate current by dividing power by voltage. This is useful for sizing power supplies, fuses, and wiring - if you need 120 watts at 12 volts, you need a power supply and wiring that can handle at least 10 amperes.
考试技巧
Current = Power / Voltage. Remember: I = P / E. 120 W / 12 V = 10 A. Divide power by voltage to get current.
记忆口诀
**I** = **P** / **E** (think 'I = P/E' = Current = Power divided by Voltage, 120/12 = 10)
实际应用示例
You need to power a 120-watt amplifier from a 12-volt battery. To calculate the current required: I = 120 W / 12 V = 10 amperes. This tells you the battery and wiring must be able to supply at least 10 amperes. You'd need a 12-volt battery rated for at least 10 amperes and wiring capable of handling 10 amperes safely.
错误选项分析
Option A: Incorrect. 0.1 amperes would be the result of dividing voltage by power (12 / 120 = 0.1), not power by voltage. Current = P / E, not E / P. Option C: Incorrect. 12 amperes would be the result of using voltage as current, which doesn't make sense. Current = P / E = 120 / 12 = 10 A. Option D: Incorrect. 132 amperes would be the result of adding (120 + 12 = 132), not the correct calculation.
知识点
Current calculation, I = P / E, DC circuits, Electrical calculations
Verified Content
Question from official FCC Technician Class question pool. Explanation reviewed by licensed amateur radio operators.