Physics things
when a source of an emf is traversed in the direction of the emf (negative term to positive term) the potential difference is
+V
when a source of an emf is traversed in the direction opposite to the emf (positive to negative) the potential difference is
-V
PE
-mu dot E
if the magnetic field is parallel to the plane and theta is 90 and the flux through the plane is
0
Surface of Earth magnetic field
0.5e-4
Ampere is defined as
1 C/s
Kinetic energy
1/2mv^2=(q^2*B^2*R^2)/(2m)
circumference of circular path
2pir
Which of maxwell's equations describes the induction of a magnetic field?
Ampere's Law
E vs B The force exerted on a charged object cannot alter the object's speed
B
E vs B The force exerted on a charged object is proportional to its speed
B
E vs B The magnitude of the force depends on the charged objects direction of motion
B
Qmax=
CV max charge on capacitor
E vs B The force exerted on a stationary charged object is nonzero
E
E vs B The force exerted on a negatively charged object is opposite in direction to the force on a positive charge
E and B
E vs B the force is proportional to the magnitude of the charge of the object on which the force is exerted
E and B
the force is proportional to the magnitude of the field exerting it (EvsB)
E and B
Induced EMF with a loop of area A in a uniform magnetic field B
E= -d/dt(BAcos(theta))
Lorentz force Law
F=qE+qvXB
The primary source of permanent magnetism in iron containing metals is the orbital motion of electrons? T/F?
False
magnetic fields can't accelerate a charged particle T/F?
False
which of Maxwell's equations describes the induction of an electric field?
Faraday's Law
Fb for current carrying conductor
Fb=(qvXB)nAL Fb=I(LXB) L is is the length A is the cross sectional area L points in direction of I
If a straight conductor of length L carries a current I, the force exerted on that conductor when it is placed in a uniform magnetic field B is
Fb=ILXB where the direction of L is in the direction of the current and Lvector=L
Newton's second Law charged particle
Fb=Sum of F=ma
because the particle moves in a circle we have a particle in uniform circular motion so..
Fb=qvB=(mv^2)/r
magnetic field throughout space when a particle with charge q and a velocity v is placed in a field it experiences a magnetic force given by
Fb=qvXB
Magnitude of magnetic force on charged particle
Fb=|q|vBsin(theta)
the direction of the magnetic force is perpendicular both ot the velocity of the particle and the magnetic field; that force magnitude is
Fb=|q|vBsin(theta)
Fb integral
I integral dsxB
Tmax
IAB when the magnetic field is parallel to the plane of the loop
T=
IABsin(theta)
the magnetic force on the wire segment of length L is
ILXB=Fb
dFb=
IdsXB
Magnetic Flux
If the magnetic field at this element is B the magnetic flux through the element is B * dA is a vector that is perpendicular to the surface and has a magnitude equal to the area dA there fore the total magnetic flux
How is a circuit breaker wired?
In series with the device it is protecting
circuits involving more than one loop are analyzed with
Kirchoff's loop rules
Junction Rule
Kirchoff's rule that states that at any junction, the sum of the currents must be equal to zero Sum junction of Currents=0
Loop Rule
Kirchoff's rule that states that the sum of potnetial differences along all elements around any circuit loop must be zero
What is the Force Law for a point charge q moving in a magnetic field B and an electric field E
Lorentz force law
what is the fundamental source of magnetic fields?
Moving Electron charge
SI unit of magnetic field
N/(Cm/s)=1 tesla (T) = N/(Am)
Period of motion (time interval particle requires to complete one rev) i equal to
T=(2pir)/v=(2pi)/omega=(2pim)/(qB)
torque on a current loop placed in a uniform magnetic field
T=muXB
The terminals of a battery are connected across two resistors in series; the resistances of the resistors are not the same. Therefore...
The current in each resistor is the same
several resistors are connected in series. Therefore...
The equivalent resistor is greater than any of the resistors in the group The equivalent resistance is equal to the sum of the resistance in the group
Torque
Torque=IAXB
if light passes through an aperture with a size smaller than the wavelenght of the light wave; optics applies T/F?
True
potential energy of the system of a magnetic dipole
Ub=-mu dot B
When a resistor is traversed in the direction opposite of the current
V=+IR (positive)
when a resistor is traversed in the direction of the current, the potential difference across the resistor is
V=-IR (negative)
biot savart law is expressed for
a current carrying wire and a current consisting of charges flowing through space where ds woudl represent the length of a small segment of space it is going through
in the velocity selector shown, electrons with speed v=E/B follow a straight path; electrons moving significantly faster than this speed through the same selector will move along....
a more complicated trajectory
what creates a magnetic field?
a moving object with electric charge a stationary conductor carrying electric current
the magnetic field can
alter the direction for the velocity vector but cannot change the speed or the KE of the particle
Magnetic field lines going into the plane
are the x's
two parallel wires that each carry a steady current exert a magnetic force on each other; the force is attractive when _______ and repulsive when _____
attractive when currents are parallel repulsive if the currents are antiparallel
KE of a charged particle moving through a magnetic field cannot
be altered by the magnetic field alone
Biot savart law must be followed
by an integration over the current distribution
When a magnet is moved towards the loop, the reading on the ammeter
changes from zero to nonzero (negative)
faraday concluded that an electric current can be induced in a loop by
changing the magnetic field
field lines are
circles concentric with the wire
briefly describe how you can generate electromagnetic radiation
connect a circuit and vary the current in the coil in time; rotate knob on power supply back and forth
Gauss is related to tesla by
conversion 1 T = 10^4G
SI unit of charge
coulomb
the magnitude of db is proportional to the
current IO and the to the magnitude ds of the length element ds
if an arbritrarily shaped wire carrying a current I is placed in a magnetic field, the magnetic force exerted on a small segment ds is
dFb=I(ds)XB
magnetic force on a small segment
dFb=IdsXB
A proton moves horizontally and enters a region where a uniform magnetic field is directed perpendicular into the field, therefore the proton will
deflect upward, moving in a semicircular path with constant speed and exit the field moving to the left
when the current in the wire is upward, the wire
deflects to the left
when the current is downward, the wire
deflects to the right
magnetic force on a negative charge is
directed opposite to the force on a positive charge moving in the same direction
electric force vector is along the
direction of the electric field
electric force does work in
displacing a charged particle
magnetic force associated with steady magnetic field
does no work when a particle is displaced because the force is perpendicular to the displacement of its point of application
The vector dB is perpendicular both to
ds (points in direction of current) and to unit vector r directed from ds towards p
a time-varying magnetic flux induces an
electric field
difference between electric and magnetic fields relatd to source of field
electric field established by isolated electric charge magnetic field of an isolated current element at some but but the isolate current cannot exist the same way an isolated electric charge can a current element must be a part of an extended current distribution because a complete circuit is needed for the charges to flow
when the magnet is held stationary and the loop is moved either towards or away from the loop, the reading changes
from zero
A change in the currently of the primary coil that
induces the current in the secondary coil not just the existence of a current
ferromagnetic substances
interactions between atoms cause magnetic moment sot align and create strong magnetization that remains after the external field is removed
emf of a battery
is equal to the voltage across its terminals when the current is zero; that is, the emf is equivalent to the open circuit voltage of the battery
what happens to the field if instead the length of the solenoid is doubled, with the number of turns remaining the same
it becomes 1/2 as large
what happens to the field if the number of turns is doubled with the length remaining the same
it becomes twice as large
what happens to the magnitude of the magnetic field inside a long solenoid if the current is doubled?
it becomes twice as large
what happens to the field if the radius is doubled?
it is unchanged
Current in a conductor sets up
its own magnetic field
to determine the total magnetic force on the wire, one must integrate over the wire,
keeping in mind that both B and ds may vary at any point
solenoid
long wire wound into the form of a helix for tight solenoid looks like a helix
total force of a particle moving in an electric and magnetic field is
lorentz force
a time varying electric flux induces a
magnetic field
magnetic force is proportional to the magnitude of the
magnetic field vector B
electric currents can be induced in a coil placed in a magnetic field by changing what three variables in time?
magnetic field, angle, area
Particle moves in a circle because the
magnetic force is perpendicular to the v and B and has a constant magnitude of qvB
two current carrying conductors exert
magnetic forces on each other
right hand rule
move from v to b and your thumb points in direction of Fb
if a charged particle moves in a uniform magnetic field so that the initial velocity is perpendicular to the field, the particle
moves in a circle, the plane of which is perpendicular to the magnetic field
the loops detects that the magnet is
moving relative to it and we relate this detection to a change in magnetic field
magnetic dipole moment coil
mu=NIA
torque exerted on a current carrying loop in a magnetic field B is
muXB valid for any orientation
E vs B The force exerted on a moving charged object is zero
neither
can a constant magnetic field set into motion an electron initially at rest?
no
does a magnetic field exert a force on a stationary charged object
no
if a charged particle moves in a straight line though some region of space, con one say that the magnetic field in that region is 0?
no
is it possible for each of three current carrying metal wires to repel both of the other wires?
no
is it possible for each of three stationary charged particles to exert a force of attraction on the other two?
no
I=
nqvA
angular speed of a charged particle
omega = (qB)/m
angular speed of the particle is
omega=v/r=(qb)/m
magnetic force acts on a charged particle
only when the particle is moving
For what orientation is the flux a minimum?
para
two headlights of a car wheel are connected in...
parallel
total mu not is the
permeability of free space
A flat conducting loop is positioned in a uniform magnetic field directed along the x axis. For what orientation of the loop is the flux through it a maximum?
perp
magnetic force vector is
perpendicular to the magnetic field
Magnetic force acting on a charged particle moving in a magnetic field is
perpendicular to the particle's velocity and the work done by the magnetic force on the particle is zero
the area vector A is
perpendicular to the plane of the loop and A is equal to the area of the loop SI unit if A*M^2
at a certain instant, a proton is moving in the positive x direction through a magnetic field in the negative z direction what is the direction of the magnetic force exerted on the proton?
positive y direction
mass spec
positively charged particles sent through a velocity selector and then into a region where the magnetic field causes the particles to move in a semicircular path and strikes a detector array at P separates ions according to their mass to charge ratio (m/q)=(rBnotB)/v
Magnetic force is _____ to the charge q of a particle
proportional
If a charged capacitor of capacitance C is discharged through a resistor of resistance R, the charge and current decrease exponentially in time according to the expressions
q(t)=(Qi)e^(-t/RC) i(t)= -Q/RC (e^(-t/RC))
if a capacitor is charged with a battery through a resistor of resistance R, the charge on the capacitor and the current in the circuit vary in time according to expressions
q(t)=Qmax(1-e^(-t/RC)) i(t)=(V/R)e^(-t/RC)
The average magnetic force exerted on a charge moving in the wire is
qVXB
Biot Savart Law says that the magnetic field dB at a point P to a length of element d that carries a steady current I is
r i distance from element ot point p and r is a unit vector pointing from ds toward P
radius of the circular path
r=(mv)/(qB)
radius of the circular path is
r=(mv)/(qB)
the magnitude of dB is inversely proportional to
r^2 where r is the distance from ds to P
electric force acts on a charged particle
regardless of whether the particle is moving
as a particle changes the direction of the velocity in response to the magnetic force, the magnetic force
remains perpendicular to the velocity
when there is no current in the wire, the wire
remains vertical
Ampere's Law
says that the line integral of B dot ds around any closed path equals mu(naught)I where I is the total steady current through any surface bounded by the closed loop
the magnitude of dB is proportional to
sin(theta) where theta is the angle between the vectors ds and r
a long vertical metallic wire carries downward electric current what is the direction of the magnetic field it creates at 2 cm horizontally east of the center of the wire
south
a long vertical metallic wire carries downward electric current what would be the direction of the field if the current consisted of positive charges moving downward instead of electrons moving upward
south
magnetic force is proportional to the
speed v of a particle
Faraday's Law of Induction
states that the emf induced in a loop is direction proportional to the time rate of change of magnetic flux through the loop
Lenz's law
states that the induced currend and induced emf in a conductor are in such a direction as to set up a magnetic field that opposes the change that produced them
Gauss's Law of Magnetism
states that the net magnetic flux through any closed surface is 0
paramagnetic
substances are those in which the magnetic moment is weak and in the same direction as the applied magnetic field
when the switch in the primary circuit is closed
the ammeter reading in the secondary circuit changes momentarily
the emf induced in the secondary circuit is caused by
the changing magnetic field through the secondary coil
when resistors with different resistances are connected in series...
the current and the charge entering each resistor in a given time interval are the same
The flux through the plane is zero when
the magnetic field is parallel to the plane surface
the flux through the plane is maximum when
the magnetic field is perpendicular to the plane
when a charged particle moves in a direction not parallel to the magnetic field vector,
the magnetic force acts in a direction perpendicular to both v and b, that is the magnetic force ie perpendicular to the plane formed by B and v
when a charged particle move parallel to the magnetic field vector,
the magnetic force on the charge is zero
A long straight wire carries a current I; which of the following statements is true regarding the magnetic field due to the wire?
the magnitude is proportional to I/r and the direction is out of the page at P
A uniform magnetic field cannot exert magnetic force on a particle when...
the particle moves parallel to the field The particle is at rest
the terminals of a battery are connected across two resistors in parallel the resistances of the resistors are not the same...therefore
the potential differences across each resistor is the same the resistor with the largest resistance carries less current than the other resistor
When resistors with different resistances are connected in parallel....
the potential differences in each resistor is the same
motor is when
the torque on a current loop causes the loop to rotate
Magnetic field lines coming out of plane
these are coming out the the paper and are dots
diamagnetic substances are
those in which the magnetic moment is weak and opposite the applied magnetic field
The area enclosed by the loop can change in
time
The magnitude of B can change in
time
the angle theta between b and the normal of the loop can change in
time
when the magnet is moved away from the loop the reading changes
to a positive value
If a charged particle is at rest, a steady external magnetic field can't get it moving T/F?
true
When EM radiation passes from medium into a vaccum, the wavelength of the light increases?
true
a charge moving with a velocity in the presence of both an electric field and magnetic field is described as
two particle in a field models with both an electric force qE and a magnetic force qvxB
Fb is zero when
v is parallel or antiparallel to B (0 or 180)
Fb is maximum when
v is perpendicular to B where (90)
magnetic force distinctive because it depends on the
velocity of a particle and because its direction is perpendicular to both v and B
the force is always perpendicular to the
velocity so the path is a circle
the force between two parallel wires is used to define the ampere as:
when the magnitude of the force per unit length between the two long parallel wires that carry identical current and are separated by m is 2E-7 N/m; the current in each wire is defined to be 1A
does a magnetic field exert a force on a beam of moving electrons
yes
does a magnetic field exert a force on a moving charged object?
yes
does an electric field exert a force on a beam of moving electrons?
yes
does an electric field exert a force on a moving charged object
yes
does an electric field exert a force on a stationary charged object?
yes
is it possible for each of three current carrying metal wires to attract one another
yes
is it possible for each of three stationary charged particles to repel both of the other particles
yes
is it possible to orient a current loop in a uniform magnetic field so that the loop does not tend to rotate?
yes
two long, parallel wires each carry the same I in the same direction. the total magnetic field at the point P midway between the wires is in what direction
zero
when a magnet is brought to rest and held stationary relative to the loop a reading of
zero is observed
