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Level 168

Magnetic Force & Magnetic Fields


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a compass in Earth's magnetic field
needle that points north = north pole and the other end = south pole
poles related to charge
like poles repel each other, and unlike poles attract
difference between poles and charges
poles ALWAYS come in N-S pairs
a south pole
if north pole of a compass needle points north, what kind of pole is the northern magnetic pole?
N*s/C*m
Tesla (T)
Gauss (G)
10^-4 Tesla (T)
the magnetic force can't do work and can't change the kinetic energy of the charged particle
Because F is perpendicular to v for the magnetic force, the particle never has a displacement. Which leads to....
Fc = mv^2/r = |q|vB
Trajectory - since F is perpendicular to v for a constant magnetic field, we have the case of centripetal acceleration
T = 2*pi*r/v
how long for one period?
if v = v(perpendicular) + v(parallel)
there is a component along B, so there is no force on that part due to v(parallel) and we get a spiral
intensity of cosmic rays bombarding Earth's surface is greatest at the...
poles, the cosmic rays can come in along B, so they are more intense there
why do magnetic fields exert a force on a current carrying wire?
the current is the motion of charged particles, so if they have some velocity perpendicular to B, there is a force
F = I*L*B*sin(theta)
Force on a current carrying wire
when a current carrying loop is placed in a magnetic field...
the loop tends to rotate such that its normal becomes aligned with the magnetic field
Torque
A "force" that causes rotation because it is exerted at a distance from the axis of rotation.
Torque continued
LW is the area, so we get:
Currents can CREATE magnetic field
since electric fields move the chafes to make the current, this is why we use the term ELECTROMAGNETISM
magnitude of the magnetic field
depends on current and DECREASES with distance from the wire as 1/r
concept question (P,Q,R)
at P, we have just 1I, but at Q, we have 2I, so BQ > BP
A loop of wire
if a wire is bent into a circular loop, it produces a magnetic field at the center with magnitude of:
The Solenoid
a set of loops
Ampere's Law
for any current geometry that produces a magnetic field that does not change in time....
delta(l)
a small segment of length along a closed path of arbitrary shape around the current
B||
the component of the magnetic field parallel to delta(l)
I
What is the variable form of rotational inertia?
E
Which letter represents heating of the vapor?
ferromagnets
groups of 10^16-10^19 form MAGNETIC DOMAINS in which the magnetic field of each atom is aligned
Induced magnetism
the domains are usually randomly oriented, but can be aligned by an external field
lodestone
a natural magnetic rock; magnetite
magnet
a body that can attract certain substances, such as iron or steel, as a result of a magnetic field
poles
the parts of the magnet where the magnetic force is the strongest
permanent magnets
always have their magnetic force
temporary magnets
objects that lose their magnetic force
noncontact forces
those forces that act on an object from a distance; gravity, magnetism
friction
a contact force; type of force between two touching surfaces
gravity
(physics) the force of attraction between all masses in the universe
electromagnet
a large number of closely spaced turns of wire that create the magnetic field when hooked up to a battery
Electric force
Fe= qE
electric field
extends outward from every charge and permeates all of space, it is in the same direction of the force that a positive test charge would experience if it entered the field.
electrical conductor
a material in which charges can move easily
electrical insulator
a material in which charges cannot move easily
Static Electricity
the buildup of electric charge on an object. When something is static, it is not moving.
electrical discharge
the loss of static electricity as charges move off an object. ex.lightning
electric current
charge per unit of time
voltage
The potential difference between two points.
resistance
a force upon an object that slows down motion
cells
changes chemical energy or radical energy into electrical energy
thermocouple
a device that converts thermal energy into electrical energy
how is a water current similar to electric current?
like electric current, water currents can carry energy and do work
what is ohm's law?
the current in a circuit depends on voltage and resistance. I = V/R, R=V/I, V= elec*R
electric power
the rate at which electrical energy is changed into other forms of energy
photocell
converts light energy in electrical energy
series circuit
a circuit in which all parts are connected in a single loop
parallel circuit
a circuit in which loads are connected side by side