Phys 313 Quiz 24

Question 1

You are given a solenoid with

length L = 20 cm
radius R = 2 cm
number of turns N = 200

and an iron bar. The bar just fits inside the solenoid, and has a magnetic permeability 2 x 10^(-2) Tesla/Amp^2.

How much current must you run through the solenoid to keep the iron bar from falling out the bottom when you tip the solenoid upright?

   Answer:  One may approximately calculate the force by 

                           change in potential energy
	             force = - ----------------------------
                             change in position

            Using the expression for potential energy of an iron
            bar inside a solenoid from the lecture on solenoids,
            one finds that the current must be about

                   1 Amp.