Transcript Magnets and Magnetic Fields

Magnetic Forces
The Force on a Moving Charge in a
Magnetic Field
Just as current-carrying wires (a stream of
moving charges) experience a force in a
magnetic field,
a single electrical charge also experiences
a force if it is moving in a magnetic field.
Magnetic force
e-
The Force on a Moving Charge in a
Magnetic Field
The magnitude of the force is given by
F = qv x B
Where B is the magnetic field in Tesla,
q is the electric charge in Coulombs
v is the velocity in meters per second
Only perpendicular components of v and B
contribute to the magnetic force.
CRT’s and Magnets
(TV and computer monitors- NOT flat
screen)
1. Electrons are produced
at the cathode.
2. They move through an
electromagnet.
3. The electromagnet
pushes them in different
direction.
4. The hit the
phosphorescent screen,
making it glow.
How the Earth’s Magnetic Field
the MAGNETOSPHERE,
protects us from moving
charges…
There are storms on
the surface of the sun
that are known as
solar flares or sun
spots.
These storms eject
electrons, ions, and
atoms out through the
corona toward space.
This is called the
“solar wind” or
“cosmic radiation”.
Earth’s Magnetic Field
The
Magnetosphere
acts like a shield
around the Earth
to protect us from
the solar wind.
Most of the solar wind is
deflected around the
Earth and moves out
toward the outer solar
system.
When the solar
wind is
particularly
intense, some of
these charged
particles
penetrate the
Earth’s
Magnetosphere.
These charged particles
gets trapped in Earth’s
magnetic field lines,
experiencing the magnetic
force that causes them to
orbit around and around
the field lines and travel
from pole to pole. They
can cause disruption of
signal from satellites and
can even cause the
destruction of sensitive
equipment inside
satellites.
But… it also can cause the atmospheric molecules
near the field lines to glow.
This causes the auroras:
Aurora Borealis, the Northern lights
Aurora Australis, the Southern lights.
Particle Accelerators
This magnetic force is used to accelerate
particles in laboratories like CERN, in
Switzerland, to study fundamental
particles and their interactions in its Large
Hadron Collider.
The magnetic force on a moving charge will
be a centripetal force, causing the charge to
move in a circular pathway.
Magnetic Force = centripetal Force
qv x B = mv2 / r
The direction of the Force is given by the
right-hand rule:
Thumb = direction of v (velocity)
Fingers = B (magnetic field)
Palm = Force on a POSITIVE charge
Mass Spectrometer
A mass spectrometer is a machine that can
determine the mass of a subatomic charged
particle by measuring the radius of the circle it
moves in while under the influence of a
magnetic field.
How a Mass Spectrometer works
First, charges are
accelerated down a
tube by applying a
potential difference, DV.
The work done on the
charge, qDV,
Next, the moving charge enters a known
transforms into kinetic magnetic field, where the magnetic force
causes circular motion.
energy:
Measuring the circle’s radius provides the
info needed to determine the mass of the
qDV = ½ mv2
charge.