Homework Help: Physics

Posted by Alyssa on Sunday, February 17, 2013 at 8:38pm.

A circular conducting coil with radius 3.40 cm is placed in a uniform magnetic field of 1.090 T with the plane of the coil perpendicular to the magnetic field. The coil is rotated 180° about the axis in 0.222 s.

(a) What is the average induced emf in the coil during this rotation?

I got 35.7mV and I am almost positive this is right.

(b) If the coil is made of copper with a diameter of 0.900 mm, what is the average current that flows through the coil during the rotation?

I used I=V/R and R=pL/A (where p is resistivity of copper 1.67e-8) and got I 481A but this is not right. Please help!

Physics - bobpursley, Sunday, February 17, 2013 at 10:01pm
I agree, b is not even close.

I=.0357volts/R

R=1.67E-8*PI*.9EE-3/(.45EE-3)^2*PI

I=.0357*.45^2*E-6*PI/(1.67E-8PI*.9E-3)=480amps

Ok, checking A, something is wrong.
V=1/2 turn/.222sec*PI*.034^3*1.09= = 0.00030313086 volts. So recheck your EMF
Physics - Alyssa, Sunday, February 17, 2013 at 10:16pm
I don't understand what you just did for A.

I used emf=change in flux/change in time

flux = magnetic field*area

according to my book, the answer for A is right. Please explain!
Physics - Alyssa, Sunday, February 17, 2013 at 11:13pm
So just for the record, the answer for A is right.

For B, when calculating the resistance R, I messed up in regards to the radii. For the length i needed to use r=.034m and for the area r=4.5e-4m. What a silly mistake.

Cheers! and thanks for responding! :)

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