Deep Dive: T5D03
The correct answer is B: R = E / I. The formula used to calculate resistance in a circuit is R = E / I, which is Ohm's Law rearranged. Resistance equals voltage divided by current. This is the same fundamental relationship as E = I × R, just rearranged to solve for resistance. When you know the voltage across a component and the current through it, you can calculate its resistance. This formula is essential for determining component values, troubleshooting circuits, and understanding how resistance affects circuit behavior. The formula R = E / I shows that resistance increases when voltage increases (for constant current) or when current decreases (for constant voltage).
Why Other Answers Are Wrong
Option A: Incorrect. R = E × I would multiply voltage and current, which gives power (P = E × I), not resistance. Resistance has units of ohms, not watts. Option C: Incorrect. R = E + I would add voltage and current, which have different units and cannot be directly added. Option D: Incorrect. R = E - I would subtract current from voltage, which is mathematically invalid due to different units.
Exam Tip
Resistance formula = R = E / I. Remember: Resistance equals Voltage divided by Current. This is Ohm's Law rearranged to solve for resistance.
Memory Aid
**R** = **E** / **I** (think 'REI' - **R**esistance **E**quals **I**nverse of current, or **R** = **E** divided by **I**)
Real-World Example
You're testing an antenna tuner. You measure 50 volts across a component and 1 ampere of current through it. Using R = E / I, you calculate the resistance: R = 50 / 1 = 50 ohms. This confirms the component value and helps you verify proper operation.
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.