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accountdracula
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Homework Statement
I'm answering a question which describes a situation in which a metal ring is dropped through a magnetic field such that, when it falls, its area is perpendicular to the magnetic field.
I need to find its terminal velocity given:
Mass : 2.66 x 10-4 kg
Magnetic flux density : 2.00 T
Radius : 2.00 cm
Resistance : 2.48 m(ohms)
Homework Equations
Emf = dBA/dt
V = IR
F = BILsin(theta)
The Attempt at a Solution
At terminal velocity, the magnetic force as a result of the ring's current must equal its weight:
mg = BIL
I'm confused about how to introduce v into the equation E.m.f = dBA/dt.
My thoughts were as follows:
If A is the area through which the ring moves in time dt then
A = pi r2vdt
e.m.f = (dBpi r2vdt)/dt
e.m.f = dBpi r2v
Dividing both sides by R :
I = (dBpi r2)/ R
I would then set this equal to mg / BL to find v.
However, in previous questions 'L' has always been a straight wire. Would you use the diameter of this metal ring or its circumference? My feeling is the circumference but I'm not 100% sure.
Also, is the way I've approached this question right?