PhysLink.com Logo

Question

Why is there resistance in wires, and when you vary things like the length of the wire, why does the resistance change?
Asked by: Rachel

Answer

The best way to answer this is through an analogy. Imagine the charge that is flowing through a wire to be water flowing through a pipe. The Rate at which the water is flowing is the current in an electrical system, how fast are the electrons moving. Resistance is what restricts the movement of the charge through the wire. The length of a pipe, the cross-section, and the imperfections in the pipe (clogs and such) all impede the flow of the water, and are analogous to how electric current is impaired as it flows through a wire. Things like making the wire longer and thinner make the resistance go up since it is harder to push charge through the wire. So you can see that resistance is inherent in every type of wire. There are cases when some materials can be cooled down to very temperatures where they have effectively zero resistance, but in everyday encounters electricity this, effect doesn't really have much bearing.
Answered by: Mike Perkins, Physics/Astronomy Major, Penn State


The reason for resistance in wire is because of the composition of the atoms such as copper, aluminum, of which a particular wire is made of and the arrangement of the atoms of these metals. When an electron passes through the wire, the electrons hit these atoms while making the journey from one end to the other giving opposition or resistance to the electrons. When this happens electrons move an electromotive force such as voltage, and in hitting these atoms, also creates heat via friction of the electrons and atoms. When the wire is lengthen, the journey is considerably longer and the resistance changes. Also, the size of the wire changes the amount of resistance. That is one reason you don't use a #22 gage lamp cord extension to supply extended power to an appliance of heavy duty. You don't have the capacity to supply enough electrons efficient enough to run the appliance.
Answered by: Joseph Toy, M.S.


Science Quote

'As long as men are free to ask what they must; free to say what they think; free to think what they will; freedom can never be lost and science can never regress. '

J. Robert Oppenheimer
(1904-1966)


All rights reserved. © Copyright '1995-'2017 PhysLink.com