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Ohm's Law · Power · Series/Parallel · Voltage Divider · RC Time Constant

V = I R P = V I

Ohm's Law — solve for any value

V
A
Ω
W
Voltage — V
Current — A
Resistance — Ω
Power — W
V = I·R  |  P = V·I = I²·R = V²/R

Power vs Resistance

R ↑ P ↓ P
P = V²/R (constant V)

Ohm's law triangle

V I R V = I × R

Series / Parallel resistor combos

Ω
Separate multiple values with commas
V
Series total — Ω
Parallel total — Ω
Series current (if V supplied) — A
Parallel current (if V supplied) — A
R_series = R₁+R₂+...  |  1/R_parallel = 1/R₁+1/R₂+...

Circuit schematics

Series R1 R2 R3 Req = ΣR Parallel R1 R2 1/Req = Σ1/R

Voltage Divider

V
Ω
Ω
A
Output voltage (Vout) — V
Current through divider — mA
Vout with load — V
Attenuation ratio — ×
Vout = Vin × R₂ / (R₁ + R₂)

Voltage divider circuit

Vin R1 R2 Vout — I = — mA
Vout = Vin × R₂ / (R₁ + R₂)

RC Time Constant

Ω
µF
V
Time constant (τ) — s
5τ (full charge) — s
Cutoff frequency — Hz
Energy stored (if V provided) — J
τ = R × C  |  f_c = 1 / (2π × τ)

Charge / discharge curve

0 5τ V τ 63%
At t = τ, voltage reaches 63.2% of final value