Summary























gc6 tb21.5
A loop of wire rotates in a uniform magnetic field. What happens to the induced emf if the diameter of the loop is doubled but all other factors remain unchanged?
A. The induced emf is four times as much.
B. The induced emf is twice as much.
C. The induced emf is half as much.
D. There is no change in the induced emf.
Answer























PSE6 31.6
A magnetic field of 0.200 T exists within a solenoid of 500 turns and a diameter of 10.0 cm. In what period of time must the field be reduced to zero if the average induced emf within the solenoid during this time interval is to be 10.0 kV?
A. 5.33 µs
B. 78.5 µs
C. 335 µs
D. 22.2 ms
Answer



















Walker5 Ex 23-6
A metal ring falls out of a region of magnetic field and into a field-free region as shown. The induced current in the ring is ______.

A. clockwise
B. zero
C. counterclockwise
Answer



















Walker5 23.27a
A loop of wire falls between the poles of a magnet as shown. When the loop is above the magnet the induced current in the loop is ______.
A. clockwise
B. zero
C. counterclockwise
Answer



















Walker5 Ex 23-8
If B = 2.71 T, ℓ = 1.25 m, and v = 3.1 m/s in the figure below, at what rate is the magnetic flux Φ changing?

A. 3.88 Wb/s
B. 10.5 Wb/s
C. 0.700 Wb/s
D. 28.4 Wb/s
Answer



















Walker5 Ex 23-6
A metal ring moves into a region of magnetic field as shown. The induced current in the ring is ______.

A. clockwise
B. zero
C. counterclockwise
Answer



















 



A. The induced emf is four times as much.
The magnetic flux is proportional to the area, which will increase by a factor of four when the diameter is doubled. The change in flux will then be four times larger, and so will the induced emf.




















 



B. 78.5 µs
Picture (1017x176, 5.5Kb)



















 



C. counterclockwise
Because of Lenz's law the current will flow counterclockwise in order to oppose the decrease of the out-of-the-page flux. The induced counterclockwise current produces an out-of-the-page flux that partially restores the decreased flux that occurs when the ring falls out of the region of magnetic field.
There is also a magnetic drag force because of the induced current, as shown.




















 



A. clockwise
The out-of-the-page flux through the loop is increasing as the loop approaches the poles of the magnet. The induced clockwise current produces an into-the-page flux that opposes the change of flux that occurs when the ring falls into the region of strongest magnetic field.




















 



B. 10.5 Wb/s
The rate of change of the area is vℓ or (3.1 m/s)(1.25 m) = 3.88 m²/s. Because the field is perpendicular to the area, Φ = BA and the rate at which the flux changes is simply (2.71 T)(3.88 m²/s) = 10.5 T·m²/s.




















 



C. counterclockwise
Because of Lenz's law the current will flow counterclockwise in order to oppose the increase of the into-the-page flux. The induced counterclockwise current produces an out-of-the-page flux that partially reduces the increased flux, slowing down the rate at which flux changes in the ring.

























Picture (550x416, 25.9Kb)

Vertical Velocity (or V2) is an Impulse Coaster at Six Flags Great America which is a coaster that is launched forwards and backwards using electromagnetic motors. You can see the magnets above the track as this trainload of riders is launched out of the station. The first launch is quite a rush and you get going faster and faster as you go forwards and backwards until you get up to 70 miles per hour.












Picture (700x466, 100.2Kb)

A magnet is suspended above a superconducting pellet because the induced currents on the surface of the superconductor create a magnetic field that opposes the magnet's field by Lenz's Law. The phenomenon is best described by the Meissner Effect.

















 
Images of magnetically levitated trains on test tracks in Japan.

Picture (600x300, 70.2Kb)


Picture (346x510, 120.3Kb)


Picture (287x415, 112.1Kb)