Physics 201- Introduction to Electricity & Magnetism
October 14- Introduction to Ohm's Law

Resistance

A high resistance means that you need a greater potential difference to move the same current.

Resistance has units of V/A or Ohm (W)

As the current goes through a resistor, it moves to a lower potential.

You could think of resistance as being like an electric version of friction.  As the current moves through a resistor it bounces around on the ions within the resistor.  With each of the collisions, the current gives up energy to the resistor.

So, what raises potential?

Emf

An emf device maintains the potential difference across itís terminals- a battery or power supply.

Forgive the poor choice of terminology.  Inside the emf device the (positive) charges are transferred (via the gremlin) from the low potential side to the high potential side (this is the "pump").  Chemical reactions, thermal energy, solar energy, etc. can supply this "unnatural" motion.  (By "unnatural" we simply mean that an external force has to do work to move the charges across the potential difference inside of the emf device.)

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 Jeff Phillips phillips@lmu.edu Loyola Marymount University Fall 2002