01. Ohm's Law

If the electrons can move freely in a conductor and the density is constant, there is a simple relationship between current and voltage:

R is the resistance of the conductor, or, abstractly, any resistance.

In a conductor of cross-section area A and length l and specific resistance ρ, resistance is:

Resistors in Series

A resistor in series with another resistor will act like one bigger resistor.

The current through each resistor of the series is the same.

The voltage U_n through one resistor R_n of the series depends on the resistor itself in the following way:

Resistors in Parallel

Each resistor in parallel with another resistor will always be used for some current.

The voltage over the parallel resistors is the same.

The current I_n through one resistor R_n of the series depends on the resistor itself in the following way:

The total replacement resistor R_a which can replace all the others will always be smaller than the smallest resistance of the set.

Reality

In reality, a metal's resistance (and thus a resistor's resistance) is dependent upon temperature. The higher the temperature the higher the resistance (usually).

Author: Danny (remove the ".nospam" to send)

Last modification on: Thu, 09 May 2013 .