The Movement of Charged Particles in a Magnetic Field

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The Movement ofCharged Particlesin aMagnetic
Field
By Emily Nash And Harrison Gray
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Preview

• Magnetic fields and how they are created
• Magnetic field of the earth
• Solar wind and how the earths magnetic field
  affects it
• Taking a look at the force that magnetic fields
  exert upon electrons by using a cathode ray tube,
  magnets, and some simple math.

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Magnetic Fields
Magnetic Fields are created by moving charged
particles, and only affect moving charged
particles.
Forces between two electric currents is what
causes a magnetic force. Two parallel currents
flowing in the same direction attract each other,
while two parallel currents flowing in opposite
directions repel each other.
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When there exists a steady stream of electrons, a
negatively charged particle, an electric current
forms, which produces a magnetic field.
This force leads to the idea of the north and
south poles of a magnetic field.
S
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Creating a Magnetic Field
It is possible to create a magnetic field by
producing an electric current, or vice versa.
When current passes through a coil of wire, it
generates a magnetic field along the access of
the coil.
This is called electromagnetism
current
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Earth's Magnetic Field
The Earth itself is a magnet, with a magnetic
north pole and south pole.
The origin of the Earths magnetic field is said
to be a result of the dynamo effect, electric
currents produced by the rotation of the
iron-nickel core.
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The Earths magnetic field continually traps
moving charged particles coming from the sun,
called solar wind.
High concentrations of these particles within the
field are called the Van Allen Radiation belts.
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Solar Wind
Magnetotail
Solar Wind consists of gases comprised of
protons, electrons, and ions which hurl towards
the earth from the sun at velocities of 450
km/sec or higher.
Bow Shock
Magnetosheath
The path of these particles change almost
directly as they hit the earths magnetosphere at
the region called the bow shock.
The impact of the solar wind causes The field
lines facing the sun to compress, While the field
lines on the other side stream back to form
a Magnetotail.
Because the charged particles of the rays are
deflected around the magnetosheath, the earth is
protected from most of the deadly radiation.
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Solar Wind Cntd
Some solar wind particles, however, do escape the
earths magnetosphere and contribute to the Van
Allen radiation belts.

• When these particles do enter the magnetic field,
  they go through three motions
• Spiral- the particle takes a spiraling motion
  around a magnetic field line.
• Bounce- the particles eventually bounce towards
  the opposite pole, where they spiral again.
• Drift- as the particle continually spirals and
  bounces, it drift around the magnetic field and
  is trapped in the magnetosphere.

In order to better understand the motion of
particles through a magnetic field, we have
conducted an experiment involving creating an
electron beam and running it through magnets as a
parallel to solar wind entering the earths
magnetic field.
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v
Cathode Ray Tube Cntd.
Since change in energy is the voltage times the
charge then ½mv²qV Therefore v v(2qV/m)
Electrons are attracted to positively
charged plate. They accelerate towards it and
small percentage escape the plate through
small hole, creating electron beam.
The potential energy of electrons is converted to
kinetic energy
120 Volts
Plate is heated and electrons boil
off. Velocity 0 Potential Energy ½ mv2
6.3 Volts
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Cathode Ray Tube
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Calculating the Velocity of the Electrons
We now know that v v(2qV/m), so we can now
easily find the velocity of our beam of
electrons.
q(charge) of an electron -1.610-19
V(volts)120
m(mass) of an electron9.1110-31 kg
Therefore vv(2)(-1.610-19)(120)/(9.1110-31)
vv4.2151013
v649106 m/s
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Bending Electron Beams
In order to predict the angle at which the
electrons are deflected, we must first
measure the force that the magnetic field
inserts upon the beam
To do this, we use the equation FqvB
Like Solar Wind, the electrons in the CRT beam
are deflected when entering a magnetic
field, therefore the electron beam bends.
Magnetic field
The force is always Perpendicular to the magnetic
field And the velocity of the electrons
Electrons
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Calculating the Strength of the Magnetic Field
In order to find the force of the magnetic field,
we must first calculate its strenghth.
Since FqvB and, according to Newtons second
law, Fmv²/r, we can deduce that qvBmv²/r Or B
mv/qr
mass 9.1110-31 kg
velocity 6.492106 m/s
Charge 1.610-19 C
And we measured the distance of the electron beam
from the magnets to be .075 meters
Therefore B (9.1110-31)(6.492106)/(1.610-19
)(.075)
B2.77210-6 tesla
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Calculating the Force of the Magnetic Field
Now that we know the strength of the magnetic
field at the electron beam, we can Calculate the
force which the field exerts upon the electrons.
FqvB
F(649106)/(1.610-19)(2.77210-6
F2.87910-18 N
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Conclusion

• Basics of Magnetic fields and electromagnetism

• The earths magnetic field and how it shields the
  earth from solar wind

• The movement of charged particles such as solar
  wind as they enter a magnetic field

• How to find the force that magnetic field exerts
  upon charged particles and the strength of the
  field itself.

• How to predict the path of a charged particle
  through a magnetic field