Electomagnetic Induction

1. Imagine a superconductor in its normal state in the shape of a ring immersed in a magnetic field parallel to the central axis (that is, perpendicular to the plane of the ring.) Suppose the ring is cooled and becomes superconducting. (a) Describe what happens to the field (b) If the ring is pulled parpendicularly out of the field, what will happen to the flux in the hole in the "doughnut"? (c) Account for the energy associated with the work done on the ring (if any) in yanking it from the field region. 2. An electron is orbiting between the poles of an electromagnet in a device called a betatron. The field is gradually being increased. How does the machine accelerate the electron? Wh... click for more

Electromagnetic Induction

1. Imagine in a remote area of the countryside a 70-kV, 60-Hz power line. A shifty local resident has erected a large open loop just below the line with the intention of drawing power. Is this possible and, if so, how would it be transferred? Where would the energy stolen come from? Would anyone be able to detect the loss? Might it be possible to bug a telephone using the same approach? Explain. Problem 1. The magnetic field of a large electomagnet is a uniform 0.140 T directed east to west. A 10.0-cm length of straight copper wire is held horizontally in the field perpendicular to it and then moved downward at 0.50 m/s. What voltage will appear across the wire? Which end is positive? ... click for more

Magnetism

1. Why is a chunk of iron attracted to either pole of a magnet? What does this tell you about the reliability of attraction as a test of whether something is permanently magnetized or not? A classic puzzle involves two seemingly identical rods, one steel and magnetized (with poles at its ends), the other soft iron and not magnetized. How can you tell which rod is which, using nothing else and not bending or breaking either rod. 2. James Clerk Maxwell confirmed experimentally that the B-field of a long straight current-carrying wire drops off inversely with distance. His apparatus consists of a lightweight disk, free to rotate, on which rest for bar magnets. No matter how larege the curren... click for more

Magnetism

1. A lovely way to shield against the Earth's magnetic field was used in a monopole experiment at Stanford University. A deflated lead-foil balloon is cooled below its critical temperature. Inflating the balloon then provides a field-free region inside of its hollow. How does it work? 2. A flat cirular coil having a diameter of 25 cm is to produce a B-field at its center of 1.00mT. If it has 100 turns, how much current must be provided to it? 3. A thousand turns of fine wire are wrapped around a thin hollow cardboard core, making a 100-Ohm coil 20.0 cm long and 2.00 cm in diameter. What B-field will exist inside the coil at its center when placed across a 20.0-V dc source? 4. Suppos... click for more

Magnetism

1. Imagine a small cylindrical permanent magnet floating above a superconducting tin disk bathed in liquid helium at around 1.2 K. The magnet was placed on the disk, and the latter was cooled below its transition temperature, at which point the magnet spontaneously jumped into the air. Explain what happened. This same kind of magnet levitation is being applied via high-temperature superconductors to produce frictionless magnetic bearings for gyroscopes, computer disk drives and the like. 2. A coaxial cable (like those used in cable TV installatins and with VCR's) consist of central conducting wire imbedded in a cylindrical insulating core which is then surrounded by another outer conducti... click for more