Exam grades
Your first exam is graded, as of right this minute. The average was 83.6 with a standard deviation of 9.5, which implies you were more clever than expected (or I was more generous in partial credit, but let's be optimists here). In any case: well done, most of you will be happy.
Do show up tomorrow to get your graded exams, you'll also get back Quiz3 and Lab2, and possibly Quiz4 and Lab3.
See you in a few hours ... we'll go over the exam and then begin with induction and so forth.
Do show up tomorrow to get your graded exams, you'll also get back Quiz3 and Lab2, and possibly Quiz4 and Lab3.
See you in a few hours ... we'll go over the exam and then begin with induction and so forth.
4 comments:
Doc Leclair,
This issue has been giving me problems in all of my review so I was wanting to clear it up right away; how do I correctly type into my calculator the magnetic field equation?
For example, on Exam 2-Summer 2008, question number 1 under MAGNETISM asks to solve for magnetic field given current & distance..so I would type in the Uo constant (4pi*10^-7) multiplied by current (I=20) and divide all of that by 2pi(distance) and distance=.80m.
When I type all of this in the calculator I come up with 3.1*10^-7 or something along those lines..this same equation has given me difficulty all wknd. Is it a matter of conversion at the end, or am I simply computing the numbers incorrectly?
To clarify, the answer should be 5uT. and I keep getting 3.16*10^-5
I've been pretty tied up all weekend, but I will check the solution tonight and see what the problem is - could be a typo.
The problem you're having is with the order of execution - you have to put things in parentheses to be totally sure it comes out right. Compare the following (try pasting them into google to compute):
(4*pi*1e-7*20)/(2*pi*0.8)
4*pi*1e-7*20/2*pi*0.8
The first case - correct - computes the product 4*pi*1e-7*20, then divides by (2*pi*0.8). In the second case, there is no reason for the calculator/computer to give precedence to the * operations over the / operation, os it would just do them all in order. This is not what you want, since it would do 4*pi*1e-7*20, divide by 2, then _multiply_ the result by pi*0.8.
Long story short: if you have compound fractions, where the denominator is a whole expression, put it in parentheses to be on the safe side. More generally, you will never go wrong grouping things in parenthesis to be sure things get evaluated correctly.
If that doesn't make sense, ask me before class tomorrow and I can explain it better at the board.
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