A metal ring 4.5cm in diameter is placed between the north and south poles of tw
ID: 2210997 • Letter: A
Question
A metal ring 4.5cm in diameter is placed between the north and south poles of two large magnets with the plane of its area perpendicular to the magnetic field. The magnets produce a uniform field between them but are pulled apart at time t=0, causing the field to have a time dependance given by B(t)=Bo-B1t+B2t^2, where Bo=1.44T, B1=0.48T/s, and B2=0.04T/s^2 (This time dependance lasts until t=6s, at which time B reaches and remains at zero.)
a) At t=2s what are the magnitudes of the emf and the electric field induced in the ring?
b) If the ring has a resinance of 0.1, what is the magnitude of the induced current in the ring at t=2s?
c) What is the direction of the induced current (clockwise or counterclockwise), if you are facing the ring with the magnetic field pointing towards you? (explain!)
Explanation / Answer
a)induced emf=-Nd/dt=A.dB/dt=r2.dB/dt=1.78 mV
E=(dB/dt)(r/2) =1.12x0.045/4=0.0126
b)R=0.1 I=V/R=17.8 mA
c)direction is clockwise according since it counteracts the increasing magnetic field.