physics magnetism q's

[jjoe00]

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Pls help these questions seem straight forward but getting wrong, i must be tripping some where..

quest 1
The self-inductance of the circuit in the figure below is 1.04 10-7 H. Find the back emf when the current is increasing at the rate of 2.15 107 A/s.

i used the L(change in current/time) and did 1.04 x 10e-7 x (2.15 x 10e7) = 2.236V... unfortunately it marked it wrong!

Quest 2 - A magnetic field of 0.63 is directed verically upward,
b) Find the magnetic flux through a flat surface of area 19 cm2 if the surface is horizontal.

this one i said magnetic flux = BAcostheta = 0.63x 19x10e-4 x cos 90 = 0
unfornately..that was wrong

quest C is the same as above except the surface is vertical.. i did the same as above but cos theta was 0 since the mag field and surface were not perpendicular to each other

phew i hate magnetism... can any one help.. thks in advance

 

[Fort]

Yeah magnetism is tough. Unfortunately, we can't help you. Go to your professor.

 

[CaptainSSO]

Those don't really seem like MCAT questions IMO. The magnestism on the MCAT essentially comes down to knowing the magnetic force, F = qvbsintheta, the right hand rule (direction of said magnetic force, perpendicular to both the current and the magnetic field), the right hand rule for the induced magnetic field surrounding a current-conducting wire, and Lenz's law (pull a current conducting circuit through a magnetic field, and the direction of the induced magnetic field will point in the direcion necessary to resist a decrease in the overall magnetic field). I'm sure that's a bit confusing, but I would recommend ExamKrackers to clear everything up.

 

[iheartmydog]

I understand that a single charged particle moving through a constant, uniform magnetic field will experience a magnetic force that will make it move in a circular motion so there will be a centripetal force, such that F = qvB(sintheta) = (mv^2)/r. So what about for currents? For a current carrying wire that is placed in a constant, uniform magnetic field, there will be a F=iLB(sintheta). But will its charged particles move in circular motion with centripetal force? Or will they move in a straight line as currents do?