Author Question: A plastic hose stuffed more or less densely with steel wool and a source of water can act as a model ... (Read 68 times)

BrownTown3 · **on:** Jul 28, 2018

A plastic hose stuffed more or less densely with steel wool and a source of water can act as a model for resistance and electric current in wires. Suppose two one-meter lengths of such a hose were stuffed identically with steel wool.

Discuss how one could use this model to determine which of the following would have greater resistance: one length; two lengths connected one after another; two lengths connected side by side, both connected to one source of water. Speculate on the answers as best you are able.

Question 2

Why is the wire connecting your dryer to the circuit breaker in your house thicker (of greater diameter) than the wire connecting a table lamp to the electric outlet?

What will be an ideal response?

soda0602 · **Reply #1 on:** Jul 28, 2018

Answer to Question 1

This exploits the model discussed above for resistance. The single lengths of hose
have the same resistivitycaused by the steel wool stuffing. Connect two hoses in series
(one after another) and the resistance increases. Connect two hoses side by side (assume
that it is possible to do so without leaks occurring), and the water has more ways to get
through to the other sidethere is less resistance. Two lengths side by side has the least
resistance of the choices offered; two one after the other has the most resistance. In fact, by
our argument, the two side by side have half the resistance of the single length, and the two
one after another have twice the resistance of the single length.

Answer to Question 2

In the book, we mention the resistivity as the basis of resistance. For a given
diameter, both pieces of wire would have the same resistivity but a longer piece will have a
greater resistance. Here, both pieces of wire would have the same resistivity but their
diameters would be different. This difference gives rise to the difference in resistance. The
thinner wire exhibits greater resistance than thicker wire. This occurs because the larger wire
allows the charges more space to get by the atoms on the lattice (this way of thinking
about currents reflects the classical Drude model of conductivity). The thicker wire can
therefore carry much more current without generating too much Joule heat.