The Movement The Movement ofof

Charged ParticlesCharged Particlesin ain a

Magnetic FieldMagnetic FieldBy

Emily NashAnd

Harrison Gray

• Magnetic fields and how they are created

• Magnetic field of the earth

• Solar wind and how the earth’s 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.

Magnetic Fields are created by movingcharged particles, and only affect movingcharged particles.

When there exists a steadystream of electrons, a negatively charged particle, an electriccurrent forms, which producesa magnetic field.

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.

This force leads to the idea of the north and south poles of a magnetic field.

N

S

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

The Earth itself is a magnet, with a magnetic northpole and south pole.

S

N The Earth’s magnetic field continually traps moving charged particles coming from the sun, called solar wind.

The origin of the Earth’s magnetic field is said to be a result of the dynamo effect, electric currents produced by the rotation of the iron-nickel core.

High concentrations of these particles within the field are called the Van Allen Radiation belts.

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.

The path of these particles change almost directly as they hit the earth’s

magnetosphere at the region called the bow shock.

Because the charged particles of the rays are deflected around the magnetosheath,

the earth is protected from most of the deadly radiation.

Bow ShockMagnetosheath

The impact of the solar wind causesThe field lines facing the sun to compress,

While the field lines on the other side stream back to form aMagnetotail.

Magnetotail

Some solar wind particles, however, do escape the earth’s magnetosphere andcontribute 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 earth’s

magnetic field.

6.3 Volts

120 VoltsPlate is heated and electrons boil off.

Velocity= 0Potential Energy= ½ mv^2

Electrons are attracted to positively chargedplate. They accelerate towards it and smallpercentage escape the plate through smallhole, creating electron beam.

The potential energyof electrons is converted

to kinetic energy

Since change in energy is the voltage times the chargethen ½mv²=qVTherefore v= √(2qV/m)

√

We now know that v= √(2qV/m), so we can now easily find thevelocity of our beam of electrons.

q(charge) of an electron= -1.6•10^-19

V(volts)=120

m(mass) of an electron=9.11•10^-31 kg

Therefore:v=√(2)(-1.6•10^-19)(120)/(9.11•10^-31)

v=√4.215•10^13

v=649•10^6 m/s

In order to predictthe angle at whichthe electrons are

deflected, we mustfirst measure

the force that the magnetic field inserts

upon the beam

To do this, we use the equation:F=qvB

Magnetic field

Electrons

Like Solar Wind,the electrons in the

CRT beam are deflected

when entering a magnetic field,therefore the

electron beam “bends.”

The force is alwaysPerpendicular to the magnetic fieldAnd the velocity of the electrons

In order to find the force of the magnetic field, we must first calculate its strenghth.

mass= 9.11•10^-31 kg

velocity= 6.492•10^6 m/s

And we measured the distance of the electron beam from the magnetsto be .075 meters

Therefore B= (9.11•10^-31)(6.492•10^6)/(1.6•10^-19)(.075)

B=2.772•10^-6 tesla

Since F=qvB and, according to Newton’s second law, F=m•v²/r, we can deduce thatqvB=m•v²/r

OrB=mv/qr

Charge= 1.6•10^-19 C

Now that we know the strength of the magnetic field at the electron beam, we canCalculate the force which the field exerts upon the electrons.

F=qvB

F=(649•10^6)/(1.6•10^-19)(2.772•10^-6

F=2.879•10^-18 N

Conclusion

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

•How to find the force that magnetic field exerts upon charged particles and the

strength of the field itself.

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

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

•Basics of Magnetic fields and electromagnetism