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Eddy currents and current induction questions

1. Homework Statement
A solenoid is connected to a power supply and a ring of metal is sitting on top of the
solenoid. When the power supply is turned on the ring jumps up off the solenoid.
a) Suppose that when you look down at the solenoid from above. The current due to the
power supply is going around the solenoid in a clockwise direction. Use Lenz' law to
determine the direction of the induced eddy current in the ring. Explain your reasoning.
b) Explain, in terms of the force on a current in a magnetic field, why the force on the
ring due to the interaction between the induced current and the magnetic field of the
solenoid is up.
c) If the current through the solenoid is suddenly reversed in direction, is the force on
the ring up or down? Explain.
2. Homework Equations



3. The Attempt at a Solution
a. I don't know if I'm doing RHR correctly but I said that since the current is clockwise, the magnetic field is downwards. By lenz law, the eddy current needs to produce a field that would oppose this downwards increase in flux. I did RHR again and said eddy current is counterclockwise.
b. The force is upwards because the magnetic field exerts a force on the induced current...?
but I thought that the force (by RHR) is supposed to be perpendicular to the current and field?
c. Not sure....but I would imagine it just being in the opposite direction (downwards) if the current is reversed (too simple reasoning?)

1. Homework Statement
When a magnet is dropped down a vertical aluminum tube, the kinetic energy of the
magnet as it exits the bottom of the tube is only about 10% of the change in gravitational
potential energy as the magnet moved from the top of the tube to the bottom. What
happened to the missing energy? What is the final form of the missing energy? Explain.
2. Homework Equations



3. The Attempt at a Solution
I said that the missing energy is lost as electrical energy...like current since the magnet going through the tube induces a current. I saw this demonstration in class and the magnet came out very slowly...maybe some of the energy was an upward force that opposed gravity and slowed the magnet's motion?
 

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