<p>Hello fellow MIT hopefuls. I would appreciate if anyone could help me with the second hand rule with magnetism. My teacher defines it as the magnetic field from a long current carrying wire is in concentric circles about the wire. However, I am a little uncertain as to how you know if the current flow or magnetic field is into the page or out of the page if they are not given. Thanks a lot!</p>
<p>haha I just had my test on that and think I bombed it. well anyway, here's how I learned it. point your thumb in the direction of the current flow. then with the other four fingers, wrap around the wire completely and the direction your four other fingers point to is the direction of the magnetic field.</p>
<p>I remember studying that for SAT II :P but I dont remember it anymore :(</p>
<p>well, think about what you said...if you have concentric circles of magnetic field lines perpendicular to the plane of the wire, then the field will go both out of the page and into the page at different points</p>
<p>say i have a current-carrying wire pointing up. just curl your fingers around it and you'll see that the mag field goes out of the page to the left of the wire, and back into the page to the right of the wire</p>
<p>I got those first two, it makes sense. The 3rd Hand Rule with the solenoid is very weird. What is the difference between a conventional current (right hand) and an electron flow (left hand)</p>
<p>never heard of a "third hand rule"; i think it's just a variant on the second right hand rule</p>
<p>conventional current is the flow of positive charge (I think--honestly, I cant remember much), while electron flow is the flow of negative charge. so naturally, you switch direction (right hand to left hand) when dealing with electrons.</p>
<p>it's just like when you use the first right hand rule to calculate v cross B or something--you can use your left hand if you're calculating the force on an electron. or you could go through the problem with the right hand rule anyway, and just remember to switch it at the end</p>
<p>sorry if i'm not making sense; i'm down with the flu</p>
<p>bump.... i'm feeling so stupid doing this..</p>
<p>is anyone going to take the AP Phyiscs C test? or B? and what's the major difference? how much calculus do you have to know for the C test? bump^^</p>
<p>I took B last year, got a 5. Taking C this year. There's a fair amount of calculus in C. go to apcentral.collegeboard.com for info</p>
<p>Yes, conventional current assumes that the charge carriers are positive, even though in reality electrons are usually the charge carriers. It makes no difference in most cases (except for hall effect, etc.), but know what the problem is giving. Usually the current direction it gives is conventional current.</p>