Friday, July 9, 2010

Explain Lenz's law

Let us study Lenz's Law,
Lenz's law :

The direction of the induced current can be found from Lenz's law, which states that the magnetic field generated by the induced emf produces a current whose magnetic field opposes the original change in flux through the wire loop. Again, consider Figure 1 and assume the slide is moving to the right. The x shapes indicate that B is into the page; thus, when the slide moves to the right, the field through the slide will get greater into the page. (The change in flux is the crucial quantity.) The magnetic field from the induced current will be directed out of the page because it will oppose the change in flux. Use the second-hand rule and place the curl of the fingers out of the page at the center of the loop. The direction of the thumb indicates that the current will flow counterclockwise. (It is not correct to state that the current is to the right because it is to the left on the top of the loop.) Conversely, if the slide moves to the left, B will decrease through the loop. The change in flux will be out of the page, and the induced current will be clockwise. The same analysis is used if an electromagnet is turned on or off.
Figure 1

A slide wire circuit generates emf.

Lenz's law is also a conservation law. If the magnetic field generated by the induced current could be in the same direction as the original change in flux, the change would get larger and the induced current greater. This impossible condition would be a better energy exchange than a perpetual motion machine.
I hope the above explanation was useful.

Thursday, July 8, 2010

Magnetic fields and lines of force


Let us study about Magnetic fields and Lines of force,
A bar magnet attracts iron objects to its ends, called poles. One end is the north pole, and the other is the south pole. If the bar is suspended so that it is free to move, the magnet will align itself so that its north pole points to the geographic north of the earth. The suspended bar magnet acts like a compass in the earth's magnetic field. If two bar magnets are brought close together, the like poles will repel each other, and the unlike poles attract each other. ( Note: By this definition, the magnetic pole under the earth's north geographical pole is the south pole of the earth's magnetic field.)

This magnetic attraction or repulsion can be explained as the effect of one magnet on the other, or it can be said that one magnet sets up a magnetic field in the region around it that affects the other magnet. The magnetic field at any point is a vector. The direction of the magnetic field ( B) at a specified point is the direction that the north end of a compass needle points at that position. Magnetic field lines, analogous to electric field lines, describe the force on magnetic particles placed within the field. Iron filings will align to indicate the patterns of magnetic field lines.
I hope the above explanation was useful.