I'll break this up into more threads soon, but if anybody is getting a head start, there are a couple of things I want to point out. In a couple of problems, you will need to find densities, atomic numbers, etc. of certain elements. This kind of info is readily available on the web, and you have a periodic table with some of this info in the back of your book. Likewise, the book contains a table of resistivities and thermal coefficients of resistivity (page 577).
The statement of part of the 10th question (SV8 17.36) is poorly phrased; part b) should read, "what fraction of the power that is generated at the power station does this loss represent."
Careful with dimensions throughout. Look at the dimensions furnished with the answers. millimeters, micrometers, percent, ...
2 comments:
I'm having trouble with problem 12 part (a). It says to assume that the cleaner has constant resistance and that the two conductors of the extension cord have a given resistance each.
To start, I found the constant resistance without the cord in place by R = V^2/P, using the rated power and the 120V.
Then, I modified my drawing to include the two resistances of the extension cord in series with the constant resistance, and calculated the observed power with P=V^2/Rtotal, summing the resistors for Rtotal. However, this yields the wrong answer, and I'm quite confused at where I'm going wrong.
Looks like you have the right start. But in the second step, the power you calculate as V^2/Rtotal will be the total power dissipated in the vacuum cleaner and the cord. You want to find the power dissapated in the cleaner alone, which will be lower because less than 120 Volts appear across it.
Post a Comment