Ohm's Law

R = V / I

V = I R

I = V / R

R - Ohms

V - Volts

I - Amps

Power dissipated in R

P = I V

P = V² / R

P = I² R

P - Watts

V - Volts

I - Amps

(Power = Joules per second)

Series Resistors

R_t = R₁ + R₂ + R₃

R - Ohms

Parallel Resistors

1/R_t = 1/R₁ + 1/R₂ + 1/R₃

R - Ohms

Potential Divider

Assuming a negligable current flows through the output, using Ohm's Law and the series resistors formula, the current (I) through the resistors is ...

I = V_in / (R₁ + R₂)

V_out = I R₂

V_out = V_in R₂ / (R₁ + R₂)

R - Ohms

I - Amps

V - Volts