GR9277 #57



Alternate Solutions 
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Comments 
Rosenlicht 20111108 14:00:08  I think you mean that the flux is constantly increasing or decreasing, but the change in flux is constant and of course discontinuous when you go from increasing flux to decreasing flux.   mike 20101006 17:38:38  As noted by herrphysik, . So the emf is only dependent on the fact that the area is changing, and not dependent on how much area is currently enclosed (this is specific to this problem). Answer B is a trick, since you see the area increasing and decreasing. Once the entire semicircle is in the B field, goes from positive to negative, but  remains fixed. Thus, answer A is the correct one.   Maxwells_Demon 20080921 08:48:59  Given the negative sign in Faraday's Law, wouldn't the induced emf in choice (A) be negative at t=0 rather than positive?
Kabuto Yakushi 20100918 09:21:56 
I know this is a two year old post but i just thought of a solution, so I'm posting for everyone. Remember that B is a vector and written as . Take the diagram to be on the xy plane, one will see that is in the negative direction hence . So the minus signs cancel out.

  boundforthefloor 20061120 23:09:45  herrphysik is right, I'd like to add the formula clarification
agaliarept 20061201 18:11:03 
Thank you. Just what I needed.

  Andresito 20060328 07:01:54  I thought that choice (B) was the correct one.
The change in the flux "with" respect to time at t=0s is zero. The only graph that show this is (B).
Intead of saying, "The change in flux is constantly increasing as the loop spins into the field, and it is constantly decreasing as it spins out of the field" it would be better to say that "the flux change is discontinous".
herrphysik 20060824 20:47:18 
The result would be something like (B) if Faraday's Law said that the emf were proportional to the total magnetic flux through the circuit, but it doesn't. It says that the emf is proportional to the RATE OF CHANGE OF MAGNETIC FLUX, and the circuit here being a semicircle spinning with constant angular velocity, the rate of chage of magnetic flux is CONSTANT.

 




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