| Quantity / topic | Formula or fact |
|---|---|
| Current | I = Q/t |
| Ohm's law | V = IR |
| Conductance | G = 1/R |
| Series resistance | RT = R1 + R2 + ... |
| Parallel resistance | 1/RT = 1/R1 + 1/R2 + ... |
| Power | P = VI = I²R = V²/R |
| Energy | E = Pt |
| Capacitance in parallel | CT = C1 + C2 + ... |
| Capacitance in series | 1/CT = 1/C1 + 1/C2 + ... |
| Capacitor energy | E = ½CV² |
| Inductor energy | E = ½LI² |
| Frequency and period | f = 1/T |
| Sine-wave RMS | Vrms = Vpeak/√2 |
| Half-cycle average | Vavg = 0.637 Vpeak |
| Inductive reactance | XL = 2πfL |
| Capacitive reactance | XC = 1/(2πfC) |
| Series RLC impedance | Z = √[R² + (XL − XC)²] |
| Resonant frequency | fr = 1/(2π√LC) |
| Quality factor | Q = fr/BW |
| Transformer ratio | Vs/Vp = Ns/Np |
| Wavelength | λ = c/f ≈ 300/f(MHz) metres |
| Half-wave dipole starting length | L ≈ 143/f(MHz) metres |
| Quarter-wave vertical starting length | L ≈ 71.5/f(MHz) metres |
| SNR | SNR(dB) = 10 log10(Psignal/Pnoise) |
| VSWR | (1 + |Γ|)/(1 − |Γ|) |
| AM bandwidth (DSB) | 2 × highest modulating frequency |
Formula and unit quick reference
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