Posted by **Spencer** on Tuesday, April 8, 2008 at 10:15am.

Shrinking Loop. A circular loop of flexible iron wire has an initial circumference of 167 cm, but its circumference is decreasing at a constant rate of 10.0 cm/s due to a tangential pull on the wire. The loop is in a constant uniform magnetic field of magnitude 0.600 T, which is oriented perpendicular to the plane of the loop.

Find the (magnitude of the) emf EMF induced in the loop after exactly time 1.00 s has passed since the circumference of the loop started to decrease.

im pretty sure ive been doing it right but as usual probaly a dumb mistake.

- physics EM -
**drwls**, Tuesday, April 8, 2008 at 10:29am
Area A is related to circumference C by

A = pi r^2 = pi * [C/(2 pi)]^2

= [1/(4 pi)]C^2

C = 1.67 - 0.1 t (in meters)

dA/dt = [1/(2 pi)] C dC/dt

= -(0.05/pi) C

V(t) = B*dA/dt = B (0.05/pi) C(t)

With B in Tesla, the answer will be in volts. Choose t = 1 second to get C. I have thrown out the minus sign, since we don't care about polarity

Check my math and thoughts. No guarantees here.

- physics EM -
**John**, Monday, March 1, 2010 at 7:50pm
Spencer is wrong. Just so you guys know

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