Download Review for Test on Chapter 8 - the law of magnetic poles. like poles

Review for Test on Chapter 8
- the law of magnetic poles. like poles repel and unlike poles attract.
- magnetic fields. magnets exert a “force from a distance” on other magnetic objects. a magnetic
field is represented by a series of lines around a magnet, representing the path the N-pole of a
small test compass would point if it were allowed to move freely in the direction of the magnetic
force.
- Hans Christian Oersted’s principle of electromagnetism. whenever electrons move through a conductor a
magnetic field is created in the region of the conductor.
- right hand rule. using conventional current (with current flowing positive to negative), we can use
the right hand rule to determine the direction of a magnetic field around a straight conductor.
1. if a conductor is held in the right hand with the thumb pointing in the direction of current
flow, then the curled fingers will point in the direction of the magnetic field lines.
2. if a coil is grasped in the right hand with the curled fingers representing conventional
current flow, then the thumb points in the direction of the magnetic field lines inside the
coil.
- measuring magnetic fields. the magnitude of the magnetic force on a charged particle depends on:
r
- the magnitude of the magnetic field ( B )
r
- the velocity ( v )
- the charge, q of the particle
- the angle ( q ), between the magnetic
field lines and the velocity of the particle.
†
therefore, FM = qvBsin q
†
†
force
† on a conductor in a magnetic field is proportional to:
r
†
- the magnetic field strength ( B )
- the current in the conductor ( I )
- the length ( l ) of the conductor
- the angle ( q ) between the conductor and magnetic field lines
†
†
therefore, FM = kIlBsin q
†
†
( k = 1 and exists only to get rid of units)
†
†
- 1 tesla ( 1T ) is the magnetic field strength present when a conductor with a current of 1A and a
length of 1m at an angle of 90º to the magnetic field experiences a force of 1N
†
or! 1T =
†
†
†
1N
A⋅ m
†
- Ampère’s law.
†
1. for a straight conductor. along any closed
r path through a magnetic field, the sum of the
products of the scalar component of B , parallel to the path segment with the length of the
segment is directly proportional to the net electic current passing through the area enclosed
by the path
†
I
(BDL1 + BDL2 + BDL3 + º) = m0 I
B(DL1 + DL2 + DL3 + º) = m0 I
B(2pr) = m0 I
†
B=
r
2. for a coil.
†
†
B=
r
†
3. for a long solenoid.
†
†
†
&
m0 = 4p ¥10-7 Tm
A
m0 NI
2r
N is the number of loops
B is the magnetic field strength inside the coil
r is the distance from the loop toward the
inside
†
†
m0 I
2pr
Ï
Ô
ÔÔ
Ì
Ô
Ô
ÔÓ
L
m0 NI
L
N is the number of loops
B is the magnetic field strength inside the
solenoid
L is the length of the solenoid
m0 is the magnetic permeability
B=
†
†
†
†
†
†
(Andrew’s Law: iNoodles is an anagram of solenoid!)
- redefining an Ampère. 1A is the current flowing through two parallel conductors placed 1m apart
in air that exerts a force of 2 ¥10-7 Nm on each other for each metre of their length
- redefining a Coulomb. 1C of charge is the amount of charge transported by a current of 1A per
†
†
second.
†
†
†
- the motor principle.
a current-carrying conductor that cuts across magnetic external
field lines
experiences a force perpendicular to both the external magnetic field and the current, which can
be found with the right hand rule (fingers are the external magnetic field lines, the thumb is the
direction of the current in the conductor and the palm is the direction of the force).
- the magnitude of force depends on:
1. the magnitude of the external magnetic field
2. the magnitude of current through the conductor
3. the angle the conductor makes with the external magnetic field
- the principle of electromagnetic induction. whenever the magnetic field in the region of a conductor
changes, electrons are induced to flow through the conductor.
- Faraday’s ring.
G
†
- the magnitude of the induced electric potential is affected by:
1. the strength of the inducing magnetic field
2. the number of turns on the induction coil
3. the rate of change or rate of motion of the inducing magnetic field.
- Lenz’s law. when inducing electron flow, the current induced flows in such a direction that the
induced field it creates opposes the action of the inducing field.