Deep Dive: T5D01
The correct answer is B: I = E / R. The formula used to calculate current in a circuit is I = E / R, where I is current in amperes, E is voltage in volts, and R is resistance in ohms. This is Ohm's Law. Ohm's Law is one of the most fundamental electrical formulas: Current equals Voltage divided by Resistance. This formula allows you to calculate current when you know voltage and resistance. For example, if you have 12 volts across a 6-ohm resistor, current = 12 V / 6 Ω = 2 amperes. Ohm's Law is essential for understanding and designing electrical circuits. It's one of the most important formulas to memorize for amateur radio.
Why Other Answers Are Wrong
Option A: Incorrect. I = E × R would give you voltage squared divided by resistance, not current. Current is voltage divided by resistance, not multiplied. Option C: Incorrect. I = E + R doesn't make sense mathematically. You can't add voltage and resistance to get current. Option D: Incorrect. I = E - R doesn't make sense mathematically. You can't subtract resistance from voltage to get current.
Exam Tip
Ohm's Law = I = E / R. Remember: Current equals voltage divided by resistance. This is Ohm's Law, one of the most important electrical formulas.
Memory Aid
**I** = **E** / **R** (think 'IER' = I equals E divided by R, Ohm's Law)
Real-World Example
You have a 12-volt battery connected to a circuit with 4 ohms of resistance. Using Ohm's Law: I = E / R = 12 V / 4 Ω = 3 amperes. This tells you 3 amperes of current will flow through the circuit. This formula is essential for understanding how circuits work and calculating current in any DC circuit.
Source & Coverage
Question Pool: 2022-2026 Question Pool
Subelement: T5D
Reference: FCC Part 97.3
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.