Common Math Problems in General Class Exam

The General Class exam includes more mathematical concepts than Technician. Don’t worry - with practice, you’ll master them all. Here’s your complete guide.

Essential Formulas

Ohm’s Law Triangle

The foundation of all electrical calculations:

    E
   ───
  I × R

E = I × R  (Voltage = Current × Resistance)
I = E / R  (Current = Voltage / Resistance)
R = E / I  (Resistance = Voltage / Current)

Power Formulas

P = E × I          (Power = Voltage × Current)
P = I² × R         (Power = Current² × Resistance)
P = E² / R         (Power = Voltage² / Resistance)

Decibels (dB)

Decibels express power ratios:

dB	Power Ratio	Meaning
+3 dB	2×	Double the power
+6 dB	4×	Quadruple the power
+10 dB	10×	Ten times the power
-3 dB	0.5×	Half the power
-10 dB	0.1×	One-tenth the power

Quick tip: Every 3 dB is a doubling or halving of power!

Common Problem Types

Problem Type 1: Power Calculations

Example: What is the power in a circuit with 12V and 2A current?

P = E × I
P = 12V × 2A
P = 24 Watts

Problem Type 2: Resistance Calculations

Example: A 120V circuit draws 0.5A. What is the resistance?

R = E / I
R = 120V / 0.5A
R = 240 Ohms

Problem Type 3: Wavelength and Frequency

Formula: Wavelength (m) = 300 / Frequency (MHz)

Example: What is the wavelength of a 7.2 MHz signal?

λ = 300 / 7.2
λ = 41.67 meters

Problem Type 4: Antenna Length

Half-wave dipole: Length (feet) = 468 / Frequency (MHz)

Example: What length for a 20-meter dipole (14.2 MHz)?

Length = 468 / 14.2
Length = 32.96 feet ≈ 33 feet

Problem Type 5: Impedance Matching

SWR (Standing Wave Ratio) indicates impedance match quality:

SWR	Match Quality
1:1	Perfect
1.5:1	Excellent
2:1	Good
3:1	Acceptable
>3:1	Poor

Reactance Formulas

Capacitive Reactance

Xc = 1 / (2π × f × C)

Where:
- Xc = Capacitive reactance (Ohms)
- f = Frequency (Hz)
- C = Capacitance (Farads)

Inductive Reactance

XL = 2π × f × L

Where:
- XL = Inductive reactance (Ohms)
- f = Frequency (Hz)
- L = Inductance (Henrys)

Study Strategy for Math Questions

1. Memorize Core Formulas

Focus on these first:

Ohm’s Law (E = I × R)
Power (P = E × I)
Wavelength (λ = 300 / f)

2. Practice with Real Numbers

Use Practice Mode to see how these formulas appear in actual questions.

3. Learn the Shortcuts

For dB: memorize the 3 dB = 2× rule
For wavelength: 300 divided by MHz
For dipole length: 468 divided by MHz

4. Use Estimation

On the exam, you can often eliminate wrong answers by estimating:

If the answer should be around 50, eliminate 5 and 500
Check if your answer is reasonable

Common Mistakes to Avoid

Unit confusion: Make sure voltage is in Volts, current in Amps
Frequency units: Convert kHz to MHz if needed (divide by 1000)
Rounding errors: The exam uses specific values from formulas
Formula mix-up: Double-check which formula applies

Practice Makes Perfect

The best way to master these calculations is practice:

General Class Questions - Practice all topics
Mock Exam - Simulate test conditions
Wrong Answers Review - Focus on problem areas

With consistent practice, these formulas will become second nature. Good luck!