Chapter 24
Magnetic Fields
Magnet
Magnetic Poles
Compass
Title: Mar 12 ­ 9:48 AM (1 of 11)
Magnetic Field ­ direction: direction of the force on the North pole of a compass.
Magnetic Field Lines ­ imaginary lines which show the direction of the magnetic field.
Magnetic Flux ­number of lines passing through an imaginary surface.
Title: Mar 21 ­ 5:00 PM (2 of 11)
Current:
(a) Electron flow (­ to +)
(b) Conventional current
flow (+ to ­) Electromagnetism:
Current in a wire sets up a magnetic field. The direction of the field is given by the "first right hand rule"
Grasp the wire with the right hand.
1. The thumb of the right hand points in the direction of the conventional current.
2. The fingers curl in the direction of the magnetic field.
http://www.walter­fendt.de/ph11e/mfwire.htm
b
Title: Mar 13 ­ 7:11 PM (3 of 11)
Title: Mar 13 ­ 7:31 PM (4 of 11)
Solenoid: a coil of wire
A current in a solenoid sets up a magnetic field inside the solenoid. Second Right hand rule:
Grasp the wire with the right hand.
The fingers curl in the direction of conventional current. The thumb points in the direction of the magnetic field at the center of the coil.
http://micro.magnet.fsu.edu/electromag/java/compass/index.html
Title: Mar 13 ­ 7:16 PM (5 of 11)
Title: Mar 13 ­ 7:33 PM (6 of 11)
Label the North Pole of the magnet
Title: Mar 28 ­ 8:08 PM (7 of 11)
Forces on currents in an applied magnetic field:
Use the right hand open flat.
1. Thumb of the right hand points in the direction of the conventional current.
2. The extended fingers point in the direction of the APPLIED magnetic field.
3. The palm points in the direction of the force.
Title: Mar 13 ­ 7:21 PM (8 of 11)
Title: Mar 28 ­ 8:14 PM (9 of 11)
Title: Mar 13 ­ 7:29 PM (10 of 11)
Thought Questions:
1. How is it possible for a magnetic compass to give a false reading?
2. Would a magnetic compass "work" on the moon?
3. A student winds a wire around a nail as in the diagram. Which end of the nail (Head or point) would be the North Pole of the magnet?
Title: Mar 14 ­ 10:28 AM (11 of 11)