MadSci Network: Engineering

Re: I have two questions. First, why does a thicker wire have less resistance t

Date: Sat Oct 31 16:07:19 1998
Posted By: Madhu Siddalingaiah, Physicist, author, consultant
Area of science: Engineering
ID: 909376515.Eg

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


Rresistance in Ohms
rresistivity of the wire in Ohms-meters (1.7 x 10-8 for Copper)
Across sectional area of the wire in meters2
llength 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

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