What is the resistance of a circuit that draws 4 amperes from a 12-volt source?
The correct answer is A: 3 ohms. For a circuit that draws 4 amperes from a 12-volt source, the resistance is 3 ohms. Using Ohm's Law: R = E / I = 12 / 4 = 3 ohms.
This is a direct application of Ohm's Law. When a circuit draws 4 amperes from a 12-volt source, the resistance must be 3 ohms. This calculation is fundamental for understanding how circuits work and for selecting proper components. The formula shows that lower resistance allows more current to flow for a given voltage, which is important for circuit design and troubleshooting.
Exam Tip
Resistance = Voltage / Current. Remember: R = 12V / 4A = 3 ohms. Simple division gives the answer.
Memory Aid
"**R** = **1**2V / **4**A = **3**Ω (think '12/4 = 3')"
Real-World Application
You're checking your transceiver's power consumption. It draws 4 amperes from a 12-volt battery. Using R = E / I, you calculate the effective resistance: R = 12 / 4 = 3 ohms. This helps you understand the load and verify the power supply can handle it.
Key Concepts
Why Other Options Are Wrong
Option B: Incorrect. 16 ohms would be close to adding voltage and current (12 + 4), but resistance is voltage divided by current, not added.
Option C: Incorrect. 48 ohms would be multiplying voltage and current (12 × 4), which gives power (48 watts), not resistance.
Option D: Incorrect. 8 ohms would be dividing voltage by half the current, which doesn't match the given values.
题目解析
The correct answer is A: 3 ohms. For a circuit that draws 4 amperes from a 12-volt source, the resistance is 3 ohms. Using Ohm's Law: R = E / I = 12 / 4 = 3 ohms. This is a direct application of Ohm's Law. When a circuit draws 4 amperes from a 12-volt source, the resistance must be 3 ohms. This calculation is fundamental for understanding how circuits work and for selecting proper components. The formula shows that lower resistance allows more current to flow for a given voltage, which is important for circuit design and troubleshooting.
考试技巧
Resistance = Voltage / Current. Remember: R = 12V / 4A = 3 ohms. Simple division gives the answer.
记忆口诀
**R** = **1**2V / **4**A = **3**Ω (think '12/4 = 3')
实际应用示例
You're checking your transceiver's power consumption. It draws 4 amperes from a 12-volt battery. Using R = E / I, you calculate the effective resistance: R = 12 / 4 = 3 ohms. This helps you understand the load and verify the power supply can handle it.
错误选项分析
Option B: Incorrect. 16 ohms would be close to adding voltage and current (12 + 4), but resistance is voltage divided by current, not added. Option C: Incorrect. 48 ohms would be multiplying voltage and current (12 × 4), which gives power (48 watts), not resistance. Option D: Incorrect. 8 ohms would be dividing voltage by half the current, which doesn't match the given values.
知识点
Ohm's Law calculation, Resistance, R = E / I, Current draw
Verified Content
Question from official FCC Technician Class question pool. Explanation reviewed by licensed amateur radio operators.