Deep Dive: T5D04
The correct answer is B: 30 ohms. For a circuit in which a current of 3 amperes flows when connected to 90 volts, the resistance is 30 ohms. Using Ohm's Law: R = E / I = 90 / 3 = 30 ohms. This is a straightforward application of Ohm's Law. When you know the voltage (90 volts) and current (3 amperes), you divide voltage by current to find resistance. The calculation shows that a 30-ohm resistor will allow 3 amperes to flow when 90 volts is applied. This type of calculation is common in circuit design and troubleshooting, where you need to determine component values or verify circuit operation.
Why Other Answers Are Wrong
Option A: Incorrect. 3 ohms would be the current value, not the resistance. The resistance must be calculated using R = E / I. Option C: Incorrect. 93 ohms would be adding voltage and current (90 + 3), which is mathematically incorrect. Resistance is voltage divided by current. Option D: Incorrect. 270 ohms would be multiplying voltage and current (90 × 3), which gives power, not resistance.
Exam Tip
Resistance calculation = E / I. Remember: R = 90V / 3A = 30 ohms. Always divide voltage by current to find resistance.
Memory Aid
**R** = **9**0V / **3**A = **3**0Ω (think '90/3 = 30')
Real-World Example
You're setting up a power supply for your station. You connect it to a load and measure 90 volts and 3 amperes. Using R = E / I, you calculate the load resistance is 30 ohms. This helps you verify the load is correct and the power supply is operating properly.
Source & Coverage
Question Pool: 2022-2026 Question Pool
Subelement: T5D
Reference: 2022-2026 Question Pool · T5 - Electrical principles
Key Concepts
Verified Content
Question from the official FCC Technician Class pool. Explanation reviewed by licensed amateur radio operators and mapped to the T5D topic.