Lecture 9/21 Chapter 22 Magnetism Flashcards
Magnets
Poles of a magnet are the ends where objects are most strongly attracted
Two poles, called north and south
Magnetic poles cannot be isolated
This differs from electric charges
There is some theoretical basis for monopoles, but none have been detected
Magnetic Earth
The Earth’s geographic north pole
corresponds to a magnetic south pole
The Earth’s geographic south pole
corresponds to a magnetic north pole
The Earth’s magnetic field
resembles that achieved by
burying a huge bar magnet deep
in the Earth’s interior
Declination
difference between directions of magnetic north and true north.
Inclination
the angle the magnetic field makes with horizontal.
Magnetic Force on a
Moving Charge
When moving through a magnetic field, a charged particle experiences a magnetic force
Where B is called Magnetic Field:
A vector quantity
Symbolized by B
The SI unit of magnetic field is the Tesla (T)
The cgs unit is a Gauss (G)
1 T = 104 G
A Few Typical B Values
Conventional laboratory magnets
25000 G or 2.5 T
Superconducting magnets
300000 G or 30 T
Earth’s magnetic field
0.5 G or 5 x 10-5 T
Finding the Direction of
Magnetic Force
Experiments show
that the direction of
the magnetic force is
always perpendicular
to both v and B
When calculating velocity
Magnetic force = electrical force
Force on a Charged
Particle in a Magnetic Field
Consider a particle moving in an external
magnetic field so that its velocity is
perpendicular to the field
The force is always directed toward the
center of the circular path
The magnetic force causes a centripetal
acceleration, changing the direction of the
velocity of the particle
Equating the magnetic and centripetal
forces:
F = qvB = (mv^2)/r
Radius of charged particle’s circular
path:
Cyclotron equation
r = (mv)/(qB)
Cyclotrons and Synchrotrons
Unlike cyclotrons, the
synchrotron’s loop is
not a spiral
Centripetal force Equation
