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Hi Danny.

Electrical resistance results from the collision of the current-carrying charged particles with fixed particles that make up the structure of conductors. The collisions result in thermal energy (heat) in the conductor.

The resistance of a wire (or any conductor) is given by the following equation:

R = r l/A

Where:

R | resistance in Ohms |

r | resistivity of the wire in
Ohms-meters (1.7 x 10^{-8} for Copper) |

A | cross sectional area of the wire in
meters^{2} |

l | length of the wire in meters |

As you can see from the above equation, thicker wires have lower resistance
than thinner wires. This analagous to a thick water pipe vs. a thin
water pipe. A thin
wire carrying a given current will have a higher **current density**
when
compared with a thick wire carrying the same current. Higher current
density
means a higher probability of collision with stationary atoms and higher
resistance.

If you have any further questions, please feel free to contact me at madhu@madhu.com

Try the links in the MadSci Library for more information on Engineering.

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