Why does a magnetic field perpendicular to a single 13.2 cm diameter circular loop of copper wire decreases uniformly from .670 T to zero. If the wire is 2.25 mm in diameter how much charge moves past a point in the coil during this operation?

The cable from the engine spins a circular magnet. The magnet is at an angle to, and partially inside of a bell shaped part that is connected to the indicator needle. As the magnet spins faster it's magnetic field causes the bell to move further in a circular motion. There is a clock spring behind the needle that keeps the bell from spinning all the way around continuously, and to return the needle to the lower numbers as the engine speed decreases.
Try opening clocks and wd40 or alcohol on the bearing inside the bell.

Try checking the battery for good contact. If you have a multimeter, check to make sure the battery has good output.

Assuming that it is a large speaker with a large magnet on the back, and it has a large cone that was designed to play 'bass', if it has been dropped (or, for example was transported in a vehicle that went over a big bump - particularly with the speaker sitting perpendicular to the floor of the car/truck), the pole piece (magnet) in the very center shifts and pinches the coil between the outer magnet and the pole piece. This stops the coil from moving in and out through the magnetic field. Because high frequencies do not require much motion of the coil within the magnetic field, if the coil itself did not get broken in the process, higher frequencies (treble) will be reproduced (however poorly), but you'll get zero low frequencies (bass). This COULD be fixable, but a speaker repair specialist with a suitable demagnetizer would be needed to reposition the pole piece, and then, the whole cone would probably need to be replaced, as well. Depending upon whether it is an expensive (JBL/EV?) or a cheap speaker, it may be cheaper just to replace it.

There should be a plate on the machine somewhere giving the voltage. If not then the only way is either by looking at the thickness of the copper winding's or if you have a part number on either the field or armature to check it against the parts drawing.Type 1 to 4 110v fields had a red and yellow brake wire,

A field hockey ball is similar to a golf ball in terms of shape and consistency however the hockey ball is larger about 72-73 cm in diameter.

http://electronics.howstuffworks.com/motor.htm

Electric motors all typically work the same way. A current is run threw a loop in this case the copper coils in the center. This produces a magnetic field. The field magnets surrounding the copper cause the center + shaft to rotate one way. Now normally once the copper center rotated to a certain point it would reverse direction. To keep this from happening the copper that contacts where the current comes in is designed such that it reverses the flow so the center part keeps rotating the correct direction. This flip flop of current repeats and thus your motor keeps rotating in one direction.

proceed with this steps and fix it. God bless you
Instructions

1. • 1 Turn on your Sony Trinitron television.
     
   • 2 Flip the power switch on your degausser.
     
   • 
     
   • 3 Maneuver the degausser's coil so that it is a few inches away from the face of the screen. Draw the center of the degausser coil around the entire perimeter of the screen, and then return the degausser to the middle of the screen.
     
   • 4 Slowly back away from the Trintron's screen. This serves to decrease the degausser's impact on the CRT's magnetic field to zero. Continue backing away until you are about five feet away from the screen
     
   • 5 Flip the power switch on your degausser to turn it off. The CRT's magnetic field should return to its normal state and the picture quality of your Sony Trinitron should improve.
     

A mag or magneto is a coil of wire that is "excited" by a permanent magnet thereby inducing a high voltage to fire the spark plug with. Most single cylinder lawnmowers use mag and point systems to fire the plug. Coil is hard mounted and the permanent magnet is part of the flywheel with the points mounted under the flywheel.

A coil is a two coils of wire, one is connected to ground on one end and the other end is connected to either a set of points or an electronic switch, either of which turns on and off the current through that coil. When the coil discharges its electrical potential, its magnetic field collapses, inducing a high voltage in the other coil which is used to fire the spark plug.

Maybe you have some kind of magnetic material on top of the TV. TV screens respond to magnetic field. If the problem is not caused by a magnetic material being near it, then it is the degauss (meaning demagnetize) circuit inside. You can also degauss a screen using electromagnet. If placed around the screen of the TV in the right way. I have never used a magnet to demagnetize a TV screen, but maybe orienting the magnet at just the proper angle may also demagnetize it by cancelling the magnetized area. You can also make a TV screen demagnetizer using a loop maybe made out of plastic tube and winding enamelled wire onto it. The loop has to be about the size of your TV screen. Make sure you put tape over the whole thing, and connect a plug so you can plug it to the ac outlet. Once plugged in, the ac current will produce magnetic field to cancell out the magnetized area, when you wave the loop around your screen. I once made this as one of my tools when I worked at a TV repairshop.

That has been damaged by some magnetic device.

Solution: You need to degauze it. (Refer to manual for specific degauze instructions)