electricity and magnetism

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descartes1982

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does anyone have a good study strategy for the electricity and magnetism section? i find this section to be the least intuitive and if there are any shortcuts you would like to share, i would appreciate your insight. thanks!

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does anyone have a good study strategy for the electricity and magnetism section? i find this section to be the least intuitive and if there are any shortcuts you would like to share, i would appreciate your insight. thanks!

Same here, so bumping this thread.
 
I was shaky onthis so I re-read TPR's chapter on it. Its long (90ish pages) but they do an AMAZING job at explaining the concepts.
 
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Just work through it with whatever material you have. Whether TPR, BR, EK, Kaplan or material online, they all give you what you need to know for the MCAT.

Try to prepare a lesson plan to teach to a class, and run through how you are going to explain each concept. It's a bit of role-playing, with the idea being that it's meant to force you into taking good, condensed notes.

This works for any other concept you are trying to master. The process of absorbing, processing, and synthesizing helps to cement it in your head.

If that sounds a bit awkward for you, then just solve EM problems, open-book. This forces you to identify what you do and don't know, as well as understand the concept or idea in order to solve the problem.

How about an example?

Random EM problem I found online:
5. Two resistors, 2.0 ohm and 3.0 ohm, are connected in parallel with a 12 V battery. Calculate: (a) the effective resistance of the circuit; (b) the current leaving the battery; (c) the current through each resistor; (d) the voltage drop across each resistor.

Okay, so we are dealing with circuits, resistors, and a parallel system. We are also given voltage and ohms. We know a basic equation that gives the relationship between some of these variables, which is V=IR. Great. I don't know what parallel circuits are, so let's look it up. Looking up parallel circuits online tells me they are circuits where current branches, and the total current is the sum of each individual component current (Itot=I1+I2...). Also, it tells me the voltage to each branch is same as the source (Vtot=V1=V2...), and the relationship of resistance is 1/Reff=1/R1+1/R2... Okay great, so far we've acquired quite a bit; let's see if we can begin solving the problem.

First, list what we know: Two resistors, 2.0 ohm and 3.0 ohm, are connected in parallel with a 12 V battery.

We can sum as: R1=2 ohm, R2= 3 ohm, V=12 V.

Now the questions:

(a) the effective resistance of the circuit
From an earlier equation, we can calculate that easily 1/Reff=1/2+1/3 ohm -> 1/Reff=5/6; Reff=6/5 ohm

(b) the current leaving the battery
We have V=IR->I=V/R; we are given V, and we just solved for R. We can think R must be Reff, since we are calculating for total current. I=12V/(6/5)ohm=10 Amps

(c) the current through each resistor;
Okay. This is getting a bit tough. Let's think back on how current behaves in our parallel system. Total current should equal the sum of each individual current, or Itot=I1+I2... Then this means we can calculate each current separately. So I1=V/R1, and I2=V/R2. We remember that V is the same across all branches, so we keep it constant.
I1=12v/2ohm=6 A
I2=12v/3ohm=4 A

(d) the voltage drop across each resistor.
A freebie! We (now) know, that voltage across each branch is same as voltage from source. So 12 v for each branch.

I got the information and problem from a "homework help" website. To see if I can find quality information on a more generalized website, I searched parallel circuits on wikipedia, and I am seeing that the information is presented just as clearly, with better diagrams and neat tricks/mnemonics.

Pretty cool. Now I know the basics of solving parallel circuits. No fair, you say, you already knew how to solve them! Actually, it's been about 4 years since I last touched an EM problem. What if the problem was more complicated, in a XYZ fashion? Then I'd just simply look up what I'd need to adjust with XYZ, reading about everything I don't understand. Okay, this is fine, but I'll forget everything! No sweat, just do more of the same type of problems, this time closed-book. You'll be forced to recall everything and stamp it into your long-term memory.

I suggest though, unlike what I did here, start with the basics and slowly build up. Having a solid foundation in the fundamentals will give you confidence to tackle harder problems.

Do this with everything you don't understand, and soon you'll too know Kung fu.
 
There can also be circuit questions in passages that you wouldn't expect to find a circuit question (so always be on the lookout!).

For example, ANY device that is added to a circuit will have the same voltage in parallel and the same resistance in series. This stays true for capacitors, resistors, or any other "device" that AAMC may add to throw you off-guard.

I suggest TPR hyperlearning for electromagnetism and circuits as well. These topics are definitely ones that must be read multiple times.
 
There can also be circuit questions in passages that you wouldn't expect to find a circuit question (so always be on the lookout!).

For example, ANY device that is added to a circuit will have the same voltage in parallel and the same resistance in series. This stays true for capacitors, resistors, or any other "device" that AAMC may add to throw you off-guard.

I suggest TPR hyperlearning for electromagnetism and circuits as well. These topics are definitely ones that must be read multiple times.

"the same resistance in series"?????? did you mean the same current is series?

if you add a device to a circuit 2 things can happen in regard to the total resistance: 1: the total resistance will decrease if you add a device in parallel
2: the total resistance will increase if you add a device in series.
correct me if i'm wrong
 
Bump.... I really need help with this section... I have used TPR and Chad but fell a little iffy on the topic.
 
You can make electricity concepts more intuitive when you compare them with either the universal law of gravitation and gravitational force on Earth in general, as well as fluids. For example, the gravitational constant g from F=mgh can often be compared to electric field E, calculated as E=kq1/r^2, or E=qd or from V=Ed. The h height above the ground from Earth can be compared to the distance d between charges, and the potential difference V can be seen as gh in F=mgh; think of the gravitational field (the thing pulling you down from a height h) similar to electric field in V=Ed (but this can be used only for non-point charges, just like F=mgh cannot be used amongst planets!). As for circuits, capacitance can be compared to fluid pressure, and potential difference as a fluid flowing from a height h, decreasing its height every time it passes through a resistor. The battery in a circuit is like a ladder raising the fluid from ground level to a height h, and that is the voltage of the battery.
 
this used to trip me up all the time, but remember the difference between a constant, uniform electric field and one generated by particles.
 
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