1. Ohm’s Law
V = I × R
From this:
I = V / R
R = V / I
2. Electrical Power
P = V × I
Other forms:
P = I² × R
P = V² / R
3. Resistors in Series
R(total) = R1 + R2 + R3
4. Resistors in Parallel
1 / R(total) = 1 / R1 + 1 / R2
For two resistors:
R(total) = (R1 × R2) / (R1 + R2)
5. Capacitors in Series
1 / C(total) = 1 / C1 + 1 / C2
6. Capacitors in Parallel
C(total) = C1 + C2 + C3
7. Frequency
f = 1 / T
8. Reactance
Capacitive reactance:
Xc = 1 / (2 × π × f × C)
Inductive reactance:
Xl = 2 × π × f × L
9. Transformer
V1 / V2 = N1 / N2
10. Efficiency
Efficiency = (Output / Input) × 100
11. LED Series Resistor
R = (Vsupply − Vled) / Iled
12. Voltage Divider
Vout = Vin × R2 / (R1 + R2)
13. Current Divider
I1 = I × R2 / (R1 + R2)
