The Earth has a magnetic Field

Electromagnetism

If a compass's north seeking pole points north, and opposite poles attract, what type of pole is the Earth's North Magnetic pole?

The direction of a magnetic field is that of an imaginary movable north pole.

What direction does the Earth's field move in?

A wire has a magnetic field.

What direction does the magnet swing when the current is turned on?

What is the direction of the field about a current carrying wire?

Right Hand Rule

A Coil can create a magnetic field

What direction does the compass swing when the current is turned on? What is the direction of this field? What is its shape?

A Magnetic Field Exerts a Force on Charged Particles.

· No force unless the charge is moving

· If moving, the direction of the force is given by the RHR.

The Magnetic Force on a moving Charge is used to Develop An Expression for the Magnitude of a Magnetic Field

The deflecting force on a moving charge varies directly with:

(a) the size of the charge

(b) the velocity of the charge

If F a q x V then we have F = kqV and = a constant

This ratio is your definition of magnetic field strength "B"

B = = =

or is called the TESLA

Sometimes "B" is called the magnetic flux density

and one tesla = or

The Formula for the Magnitude of the Magnetic Force on a Moving Charge

If B = then F = Bvq where B and v are perpendicular to each other

Because the velocity of the charged particle is not always perpendicular to the magnetic field, we take the perpendicular component of the velocity to calculate the force.

F = Bvq sin ø

Magnetic Field inside a Solenoid

Depends on: (1) current (2) turns per unit length

therefore B ∞ _{I and}B = a constant x _I

^{this
constant = the magnetic permeability of the core "µ"}

^{In this
case µ = the permeability of free space µ}_o

^µ_{o
= 4π x 10}^-7 ^{and B = µ}_o _I

_However _{may already be calculated as turns per meter (n)}

^{then B =}^µ_o^nI

^{NOTE ONE
OTHER IMPORTANT EQUATION FOR MAGNETIC FIELD}

^{The
Magnetic Field outside a long straight wire}

^{The
field outside a long straight wire varies with}

^{(1) the
current (2) inversely with the distance from the wire}

^{therefore B = a constant X}^{the constant is}

^{that is
B =}^X

^{Magnetic Force on a Current Carrying Wire}

^{When
considering standard current (moving positive test charges) the wire feels a
force in a direction given by the RHR}

^{RHR: The
many fingers point in the direction of the many field lines. The thumb points in
the direction of the current direction. The palm pushes in the direction of the
force.}

^{The
magnitude of the force on each charge in the wire is given by}

^{F = qvB}

^{The
force on the wire must be the sum of the forces on all the charges in the wire.}

^{In the
formula F = qvB substitute v =}⁼

^{and q = I x ∆t}

^{We get,
F = B}^{, cancel the ∆t}

^{F = BIl}

^{For a
wire at an angle in the field:}

^{Use the
perpendicular component of the field to the wire direction so
that, F = Bil sinø}

^{_________________________________________________}

^{CROSSED FIELDS}

^{THIS
DIAGRAM SHOWS THE DIRECTION OF A DEFLECTING FORCE ON A CHARGED PARTIACLE IN
:}

^{(A) AN
ELECTRIC FIELD (B) A MAGNETIC FIELD}

^{NOTE
THAT WHEN USED THIS WAY THE FORCES ARE IN OPPOSITE DIRECTIONS AS SHOWN BELOW:}

^{It is possible to
cross electric and magnetic fields so that the deflecting effect of the electric
field is just cancelled by the deflecting effect of the magnetic field.}

^{The
length of the plates is the same as the width of the magnetic field.}

^{Magnetic
field into the page}

^{The
electron stream is coming from left to right}

^{Here
force from electric field = force from magnetic field}

^{qvB = qE
cancel the charges "q"}

^{vB = E and
v =}

^{The Mass
Spectrometer}

^{A
velocity selector uses crossed fields to allow only those ions of known velocity
to enter. This or another magnetic field curves these moving charges so that
they strike a photographic plate. Different masses strike at different
positions.}

^{The velocity selector gives us V =}

^{In the spectrometer the force on each
ion is given by}

_{F = BVq but F =}_{therefore BVq =}_{, cancel V's}

_{to get mV = qBR solve for m}

^{m =} _{and substitute} ^{V =}_{m
=}

_{or solve for R
using velocity,}

_{R =} _{note for
ratio questions}

^{Torque producing
force on a loop in a magnetic field (not on the Final Exam)}

^{Torque = force x
lever arm}

^{T = F x d
where
F = Bil
substituting we get}

^{T = (B i l)x d
where l = the length and d = the width of the loop}

^{therefore l x d = A (area) of the
loop and T
= BiA}

^{For a
coil
of n turns torque
T = BiAn}

^{Motors, linear and
rotary}

^{Elementary Rail Motor}

^{Rotary Motor: same theory as for a
loop. T = BiAn}

^{center coil = the armature}

^{current reversal = split ring
commutator}

^{field magnets are often
electromagnets}

^{D.C. Motor}

^{__________________________________________}

^{In an electric meter, electric torque
is balanced against the torque of the resistance spring.}

^T_spring^{= kø (ø = angle of twist)}

^T_coil^{= T}_spring

_{BiAn = kø ø =} _{and ø ∞ i Gore P. 233 (1-3)}

_{Magnetic Field
Produced by a Long Straight Wire}

_¸

_{B ∞}_{therefore
B = k}_{this is AMPERE'S
LAW}

^here^{k =}⁼_{=
2 x 10}^-7

_{B =}_{2 x 10}^-7

_{The Force Between
Two Long Parallel Conductors_}

_F₂_{= i}₂_l₂_B₁_{but B}₁_{= k}

^Substituting_F₂_{= k}

_{Gore P.238 (1-3) Review P. 239 (1-21)}

_{Another definition of the amp. One
amp flows when the force between two lengths of parallel wire 1.00 m apart is}_{2.0
x 10}^-7_N/meter.

_{Concentric magnetic field lines
encircle a current carrying wire. The direction of the lines is given by the RHR
for standard current, and by the LHR for electron flow.}

_{Two parallel wires carrying current
in the same direction attract_each other.}

_{Two parallel wires carrying current
in opposite directions repell each other.}