Topic: Physics Test Tomorrow morning..

[BigMike]

Hey guys

I'm studying for my physics 4b test tomorrow morning at 8am. I think im ready and my brain is about to explode too.

We are going over circuits dealing with resistance and capacitance and this is the "easiest test of the semester" according to my instructor. The first test kicked everyone's ass. The class average was 56% it was over gauss's law with particle charge and charge density of different conductors and insulators. 

So now we are on RC Circuits and our test is tomorrow so im studying but I needed a break so here I am
Circuits sounds simple, but we are dealing with potential voltages, charges, electromotive forces, currents, ohm's law, electron drift velocities, equivalent resistances using loop rules and junction rules from some guy named Kirchhoff, and temperature coefficient of resistivity 

Wanna a sample?? Here's something I found on the net about RC Circuits

Code: [Select]

RC circuits are circuits that contain both resistors and capacitors. In a DC circuit (or, steady-state circuit, or constant current circuit), a capacitor acts like an open switch. Its steady-state voltage will be V = Q/C and will be equal to the voltage of the battery. However, when the switch is first closed for the circuit, charge must flow until the capacitor is charged. This may only take a fraction of a second, or a few seconds. This is called a transient current.
Consider a simple loop circuit which has a battery with terminal voltage Vbattery, a resistor R, a capacitor C, and a switch. Just before the switch is closed the current is zero. Just after it is closed a current flows and the capacitor starts to charge. Its voltage will be V = Q/C. By the time Q grows until Q/C = Vbattery, the current will be zero. This early current is the transient current. Let us write Kirchhoff's Loop Law for the circuit:
Vbattery - I R - Q/C = 0
Let us note that the current I can be written as I = dQ/dt. The expression then becomes:
Vbattery - (dQ/dt)R - Q/C = 0
The solution to this equation is:
Q = (C Vbattery)(1 - exp(-t/RC))
Note that aftera long time exp(-t/RC) becomes equal to 0, and the charge is constant. If we take the derivative of Q with respect to t, we get:
I = dQ/dt = ((Vbattery)/R)exp(-t/RC)
We see that after a long time, the current is zero. The quantity RC is called the time constant. It has units of time, and determines how fast a capacitor charges and discharges.
If we start with a charged capacitor, and have only a resistor and an open switch in the curcuit, we can then discharge the capacitor by closing the switch. The Kirchhoff's Loop Law equation becomes:
- I R - Q/C = 0
Again, using I = dQ/dt, we have :
- (dQ/dt)R - Q/C = 0
The solution is:
Q = Qo exp(-t/RC)
Here Qo is C Vbattery. Again, using I = dQ/dt, we have:
I = (Q0/RC)exp(-t/RC) = (Vbattery)/R)exp(-t/RC)
Both the charge and the current become zero after a time as the capacitor is discharged. For a measure of the time we use the time constant t = R C. When t = R C, the exp(-t/RC) = exp(-1) = 0.37, or the charge on the capacitor is down to just over one-third of the original value.
oh man I need to just stick to Toyota trucks

[BigMike [OP]]

d00d what is wrong with you

[Prismo]

that link popped up while doing a search on CT-20 turbo schematics & repair instructions. Pretty weird, huh?

[WHITE_TRASH]

d00d what is wrong with you

would you like the list in chronoligical order or just a random event listing?? 

[Prismo]

Yep, it would end up being a longer thread than the $300 one.

[WHITE_TRASH]

DAMN!  I didnt think it would be that long of a list, maybe you and brainless should get the same shrink.  I think with that kinda patients he would end up being a patient himself. 
 

[BigMike [OP]]

ok, it's 6:21am now. I've been up since 5am and I think Im really ready now so I'm gonna take a nap until 7:15 or so.

wish me luck!

[BigMike [OP]]

Holy crap that test sucked

I feel really good about it though, but one question took me more than an hour to solve. I've got my TI89 set to store the last 80 entries on it, and I filled it all up. Dang. 80 times I used the calc. no wonder American school systems suck

Just for an idea, the first question was to find the ratio of the diameters of a 24 gauge copper wire and a 26 gauge copper wire, but we were only given the information about each wires resistivity within a mile length. So that took me a while, and then the hard one was I had to find out 3 currents across three different resistors out of a 4 loop circuit with 4 junctions, 2 batteries, and numerous other resistors.

Everyone stayed until the very last minuet. I think only one person left, and I bet it's because he gave up

So now we are going to learn about magnetism and this is supposed to be the hardest test that the college offers in the physics department. Yeah thanks for saying that teach, geeze

[Prismo]

Physics is actually very cool, just a major pain to learn. Organic Chemistry was my least favorite.

[Mike D]

Well last year i did free body diagrams and best values so beat that bigmike...jk

[CTENG in KS]

Hope you did well...I like Kirchoff's laws, made EE a lot easier.  What are you studying...engineering?

[BigMike [OP]]

Im studying suicide... Going for tripple majors: Mechanical E, Physics, and Math minor

 

[BLACKDOG]

Holy crap!!! props to you dude! I'll be glad to get out with an AA in Fire technology and EVENTUALLY a BA in business administration

Me and school are like mixing Hard liquor with Beer
Not a good idea!!

[BigMike [OP]]

Well I got my test back and I didnt to good or exteremly bad, got 61 out of 85. just barely a C. The multiple choice kicked my arse, lost 15 points on those alone. I think they suck because you can't get partial credit for your work. I crossed up one plus sign with a minus sign and lost credit for the whole thing.

So now my over all class grade has dropped to a high C. Only got 2 tests left, so I've really gotta pick it up- 

[Mike D]