Summary




























POP5 QQ23.4
A given applied force of magnitude Fapp results in a constant speed v and a power input P. Imagine that the force is increased so that the constant speed of the bar is doubled to 2v. Under these conditions, what are the new force and the new power input? Serway PoP5 figure 23.11
A. 2F and 2P
B. 4F and 2P
C. 2F and 4P
D. 4F and 4P
Answer



















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























POP5 QQ23.4
Consider the physical system shown in the figure. If the current in the wire changes direction, in what direction will current be induced in the circuit loop? wire and circuit loop Walker5e Figure 23-39
A. clockwise
B. counterclockwise
C. zero
Answer



















PSE6 31.34
The current in an r = 2.00 cm, n = 1000 turns/m solenoid oscillates as
I = (5.00 A) sin(100πt).
What is E at r = 1.00 cm and t = 3.33 ms?
A. 787 V/m
B. 16.7 V/m
C. 0.202 kV/m
D. 4.94 mV/m
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































 



C. 2F and 4P

solution equation














 



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. counterclockwise
answer image for upward wire current and out-of-the-page magnetic field

answer image showing into-the-page flux and induced current
Because of Lenz's law the current in the circuit will flow in a direction that produces an out-of-the-page magnetic flux, in order to oppose the into-the-page change of flux that occurs when the electric current in the wire changes direction.




















 



D. 4.94 mV/m






















 



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.




The US Navy is finalizing the technology needed to replace its explosive shells with high speed projectiles launched by rail guns. Take a look at a video demonstration, but note that widespread implementation is not going well. Read more at Wikipedia.

US Navy railgun
Photograph taken from a high-speed video camera during a record-setting firing of an electromagnetic railgun (EMRG) at Naval Surface Warfare Center, Dahlgren, Va., on January 31, 2008, firing a 3.2 kg projectile at 10.64MJ (megajoules) with a muzzle velocity of 2520 meters per second. The Office of Naval Research's EMRG program is part of the Department of the Navy's Science and Technology investments, focused on developing new technologies to support Navy and Marine Corps war fighting needs. This photograph is a frame taken from a high-speed video camera. U.S. Navy Photograph (Released)





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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.



rail gun launch

Here are artist sketches of using electromagnetic induction to assist in launching a space vehicle. Boeing is working on developing this technology, as is NASA.













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