PHY 2185 exam 3
cross product with unit vector and itself
0
unit vector dotted with itself
1
1 T=
1 N/(A*m) = 1 Wb/(m^2) = 10^4 G
3 ways to induce an EMF
1. vary magnetic field 2. vary the area of the coil 3. change the angle between B and A
An electron is traveling due south in a region of space at a constant speed.What can you conclude from this situation regarding the presence anyelectric and/or magnetic fields?
Both the electric and magnetic field might be non-zero, but they areperpendicular to each other in the region
if a charged particle enters a region of space with both electric and magnetic fields present, the force on the particle will be
F= Fe + Fb = qE + q(vxB)
soft magnetic material
Magnetic material that is easy to magnetise and demagnetise like Iron
Which one of the following statements concerning the magneticfield inside (far from the surface) a long, current-carrying solenoidis true?
The magnetic field is non-zero and nearly uniform.
A copper cylinder has an outer radius 2R and an inner radius of R and carries acurrent i. Which one of the following statements concerning the magnetic fieldin the hollow region of the cylinder is true?
The magnetic field within the hollow region is equal to zero tesla.
Do parallel currents attract or repel?
They attract
Do antiparallel currents attract or repel?
They repel
if a charged particle has a component of its velocity perpendicular to B, then its path will be
a circle. if it also has a component of velocity parallel to B, it will move forward as well. the resulting path is a HELIX
solenoid
a long wire wound in the shape of a helix
the direction of v changes, but the magnitude of v remains the same. which situation does this apply to
a particle moving in a circle at constant velocity
in determining the direction of the current in an amperian loop, when your fingers curl in the direction of integration, what direction does your thumb point
a positive current; currents in the direction opposite to ur thumb are negative
flux change can be created by
a) change in B or I creating that field that is dI/dt b) change in area A c) change in angle between B and normal
the region of space surrounding a moving charge includes a magnetic field. what will this charge also be surrounded by
an electric field
opposite poles
attract
the magnetic force acting on a charged particles with a velocity through a magnetic field is always perpendicular to
both velocity and magnetic field (v and B)
two parallel wires have currents that have the same direction, but differing magnitude. the current in wire A is I and the current in wire B is 2i. what is a true statement concerning this
both wires will attract each other with the same amount of force
for a particle moving in a circle, equate magnetic force to
centripetal force (mv^2/r)
when the velocity is perpendicular to the magnetic field, the particle travels in a
circle
method of finding direction of magnetic field inside a solenoid
curl fingers in direction of current; thumb points in direction of magnetic field
hard magnetic materials
difficult to magnetize, but don't lose magnetism easily
direction of current element IdL or IL is
direction of drift velocity of carriers (electrons)
in determining the direction of the current in an amperian loop, what direction should your fingers curl in
direction of integration
direction of magnetic field
direction that a North Pole of a compass needle points in that location
most likely source of earths magnetic field
electric currents in the liquid part of the core
true or false magnetic poles can be isolated
false; if a permanent agent is cut in half repeatedly, you will still have a north and South Pole (differed from electric charges)
true or false stationary charged particles interact with a magnetic field
false; stationary charged particles do not interact with a magnetic field
true or false magnetic field lines are open loops
false; they are closed, continuous loops, without a beginning or an end
magnetic field lines direction in a magnet
field liens emerge from North Pole and enter through South Pole
if velocity of a particle has components, what shape does the particle travel in
helical motion ; the perpendicular component determines the radius of the helix and the parallel component determines the pitch
ampere
if 1 A of current flows through two conductors which are 1 meter apart, then the force between them is exactly 2*10^-7 N
if the magnetic field is into the paper, what is the direction of station of a positive article and what is it of a negative particle
if B is into the paper, a positive particle is CCW and a negative particle is CW
At a distance R from a current carrying wire, what is the directionof the magnetic field relative to the wire?
in the direction that is perpendicular to both the wire and to the radial direction
in Lenz law problems, the system is going to try to maintain a state of equilibrium. what's the first question to ask
is the flux increasing or decreasing? if its increasing, the system will try to decrease the flux. this means magnetic field points in opooritie direction. if its decreasing, the system will try to increase it. magnetic field will point in same direction (for the induced magnetic field will be in same direction)
the earths geographic South Pole corresponds to the
magnetic North Pole
the earth's geographic North Pole corresponds to the
magnetic South Pole
a charge moving through a magnetic field experiences a
magnetic force
magnetic fields affect ________ ___________
moving charges
every current-carrying conductor produces a magnetic field because
moving electric charges (which constitute a current) inherently create a magnetic field around them.
solenoid magnet
multiple, tightly spaced loops of wire. often called an electromagnet, and inserting a soft iron bar will magnetize the bar
work=f dot dr = F * delta r *cos theta. since displacement is parallel to velocity, then delta r (displacement) is perpendicular to F, the magnetic force does
no work
the direction of induced emus and currents always _________ the change in flux that produced them
oppose
the magnetic field ________ of a solenoid is very weak or zero
outside
RHR for magnetic force
point fingers in direction of velocity, curl fingers in direction of magnetic field. thumb points in direction of force on a POSITIVE CHARGE
As a charged particle moves freely in a circular path in the presenceof a constant magnetic field applied perpendicular to particle's velocity, its KE
remains the same
like poles
repel
a charge moving in a. magnetic field has constant
speed, since KE=1/2 mv^2, it has constant KE too change in kinetic energy = work (since no change in KE, no work is done)
when a magnetic flux through a surface changes, the magnetic field due to any induced current produces a flux on its own, through the same surface and in opposition to
the change
the value of the magenta force is zero when
the charge moves parallel to the field lines
the value of the magnetic force is max when
the charge moves perpendicular to the field lines
poles of a magnet
the ends where objects are most strongly attracted
Lenz law
the induced emf is in such a direction as to oppose, or tend to oppose, the change that produces it
A charged particle moves in a straight line in a region of space with B field.Which of the following answers is true?
the magnetic field in the region has 0 component perpendicular to particle velocity
magnetic moment vector tries to align itself with
the magnetic field, which makes the coil rotate with a torque
a charge particle is moving through a region of space. which is true?
the magnetic force has a zero component parallel to v
when a charged particles moves in a non-uniform magnetic field, what happens
the particle becomes trapped and moves back and forth
True or false a magnetic field surrounds a properly magnetized material
true
the work done to move a charge around a circle is zero true or false
true
true or false all agents have at least one North Pole and one South Pole
true
true or false an unmagnetized piece of iron can be magnetized by stroking it with a magnet
true
true or false changing magnetic fields can create electric fields
true
true or false moving charges produce magnetic fields
true
true or false the high temps of the earths core prevent the magnetized materials from retaining permanent magnetization
true
true ro fasle magnetism can be induced
true
the field inside a solenoid is nearly ______
uniform
for lenz law, how to figure out direction of current
use RHR. draw the object with either magnetic field pouting in or out on each side (x and dots). analyzing one side, curve fingers so they make sense with x and dots, and thumb points in direction of current
if a charged particle enters a region of space with both electric and magnetic fields present, the value of the charge's speed can be adjusted so that F net = Fe + Fb =0. what happens when
v = E/B
region of space with crossed E and B fields
velocity selector
