Transcript Magnetism Review Answers

Magnetic field lines: lines of force
representing the magnetic field around
a magnet
 Magnetic pole: the end of the magnet
which produces magnetic force
 Magnetic field: the space around a
magnet through which magnetic force
acts

ALNICO magnet: a magnet made up of
the elements of aluminum, nickel, and
cobalt; these three metals when
combined are ferromagnetic
 Magnetic domain: a cluster of atoms
which have aligned magnetic fields
 Electromagnet: a current-carrying coil
of wire

Magnetic declination: the difference
between the location of the true North
pole and the magnetic North pole
 Aurora borealis: also known as the
Northern Lights, colored lights seen in
higher latitudes due to charged particles
interacting with Earth’s magnetic field in
the upper atmosphere

Transformer: an iron core with two coils
of wire (primary and secondary), it
changes voltage; step-up = increases
voltage, step-down = decreases voltage
 Electromagnetic induction: generating
electricity by moving a coil of wire in a
magnet’s magnetic field

Like charges and poles repel
 Opposite charges and poles attract
 Both charges and poles exert forces
which can act over a distance – they do
not have to have direct contact for the
force to be experienced

Electric charges can be separated from
each other – can remove negative
charges from an object
 Magnetic poles cannot be separated
from each other – trying to break a
magnet in half to separate the North
from the South does not result in
separate poles – just two smaller
magnets


The magnetic field lines leave the north
pole, curve around, and enter the south
pole.

You can see the magnetic field lines by
sprinkling iron filings over the magnet.
The filings will line up to show the field
lines around the magnet.

The magnetic field is strongest at the
poles.

Magnetic fields are created by moving
charges, like electrons spinning or
electrons flowing through a wire.

An electron

Most materials have atoms which have
paired-up electrons so the magnetic
fields of all the electrons cancel each
other out so there is no remaining
magnetic fields.

Each iron atom has 4 unpaired electrons.
Their magnetic fields add to each other
to produce a strong magnetic field in
each atom.

The domains in the permanent magnet
line up one direction, while the domains
in the nonmagnetic material are
randomly arranged. When the domains
line up, the magnetic fields add together
creating a stronger permanent
magnetic field.

Yes, if the material contains some iron or
ALNICO. It must be put into a strong
magnetic field and it will be become
temporarily magnetized. This is because
the magnetic field will cause the random
domains to line up. Once the magnetic
field is removed, the domains will return
to their random, unaligned state.

Heating them, dropping them, or
repeatedly hammering them. This
causes the domains in the magnet to
become unaligned and randomly
arranged.

Oersted discovered that electricity
moving through a wire caused a
magnetic field to be created. He was
conducting electric circuit experiments
and had a compass near his circuit.
When a electric current went through
the circuit, the needle of the compass
was deflected.

The magnetic field will also reverse its
direction.
A coil of wire is placed inside a permanent
magnet.
 When electricity goes through the wire, the
coil of wire becomes an electromagnet
and interacts with the magnet’s magnetic
field.
 The wire then spins. Every 180o the current
reverses direction so that the wire keeps
spinning and spinning. (Electromagnet’s
magnetic field also keeps reversing.)
 Motors convert electrical energy into
mechanical energy.


The motion of charged particles within
the molten part of Earth’s core is thought
to generate the Earth’s magnetic field.
It reduces the intensity of cosmic rays
coming from the sun.
 It traps the Van Allen Radiation belt
which can sometimes interact with the
Earth’s magnetic field to produce the
Northern lights.

The number of loops – more loops in the
coil will increase the strength
 The amount of current – the greater the
current through the coil will increase the
strength
 The presence of an iron core – if an iron
core is present it makes the
electromagnet stronger


Michael Faraday
Move a wire in and out of a magnetic
field
 Move a magnet in and out of a coil of
wire

A coil of wire is located inside a
permanent magnet – just like a motor.
 When you turn the coil of wire, electricity
is generated because the wire is moving
within a magnetic field.
 So, electricity is produced when the coil
of wire is spun within the magnet.
 Generators convert mechanical energy
into electrical energy. (opposite to
motors)


Alternating current (AC)
The number of loops in the wire – more
loops will produce more voltage
 The strength of the magnet – the stronger
the magnet the more voltage produced
 The speed of rotation of the wire – the faster
it spins, the more voltage produced


See answer to question #19
OMIT

The field lines should leave the north pole
with arrows pointing out of the north
pole, curve around, and then enter the
south pole. So, the arrows should point
at the south pole.
The lines will leave and move up and
curve way from the north poles. They do
not touch each other. The arrows point
outwards.
 For two south poles, you see a similar
pattern with the lines curving up and
away from the poles, but the arrows
point towards the south poles. The
arrows point inwards.


The lines will move from the north pole to
the south pole. So the arrows point to
the south pole and away from the north
pole.
L = 0.6 m
B = 0.400 T
I = 4.00 A
F=?
F = BIL
= (0.4)(4)(0.6)
F = 0.96 N
L = 2.0 m
I = 12 A
F = 0.50 N
B=?
F = BIL
0.50 = B(12)(2)
24
24
B = 0.021 T
F = 0.96 N
I = 5.6 A
B = 0.37 T
L=?
F = BIL
0.96 = (0.37)(5.6)L
2.072
2.072
L = 0.46 m
Q = 1.6 x 10-19 C
B = 0.75 T
v = 4.8 x 107 m/s
F=?
F = BQv
= (0.75)(1.6 x 10-19)(4.8 x 107)
F = 5.76 x 10-12 N