What the ASVAB is actually testing
Ohm's Law and power calculations make up the core of the Electronics Information (EI) subtest. The questions are predictable: you get two values, asked for a third. The entire section rewards knowing three equations and being able to rearrange them quickly under time pressure.
Ohm's Law: the foundation
V = IR — Voltage equals Current times Resistance.
Think of it like water pressure in a pipe: voltage is the pressure, current is the flow rate, and resistance is how narrow the pipe is. More resistance, less current for the same voltage.
Memorize the triangle shortcut:
V
-----
I × R
Cover what you want to find — the remaining arrangement is your formula:
- Cover V → V = I × R
- Cover I → I = V / R
- Cover R → R = V / I
Power: two forms you need
P = IV works when you have both current and voltage.
When you only have current and resistance, skip the middle step: P = I²R
When you only have voltage and resistance: P = V²/R
All three give the same answer for the same circuit. Use whichever saves you a calculation step.
The doubling trap
Test makers love asking what happens to power when you change one variable:
- Double voltage (constant R) → power quadruples (P = V²/R — V is squared)
- Double current (constant R) → power quadruples (P = I²R — I is squared)
- Double resistance (constant V) → power halves (P = V²/R — R is in denominator)
Recognizing the squared relationship is faster than recalculating from scratch.
Units to keep straight
| Symbol | Quantity | Unit |
|---|---|---|
| V | Voltage | Volt (V) |
| I | Current | Ampere (A) |
| R | Resistance | Ohm (Ω) |
| P | Power | Watt (W) |
Don't let the variable V (voltage) and the unit V (Volt) trip you up — context makes them clear.
Study approach
Write out all three power formulas on a scratch card and drill substitution problems. The EI section moves fast — you want Ohm's Law rearrangements to be automatic so you can spend your time on the harder circuit-type questions.