Transcript Electromagnetism

Electromagnetism
A study of the relationship
between magnets & electricity.
Electricity
• Electricity is the
movement of
electrons.
• Electricity can be
one of 2 types.
– 1) Static
– 2)Current
Static Electricity
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Thales (left) & William Gilbert (right)
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- If you rub your feet on carpet and
touch a doorknob, it will shock you.
This is called static electricity. (an
accumulation of electrical charges
made by gaining or losing
electrons).
Static electricity was discovered and
tested by Thales, a Greek who lived in
600 BC. He observed and noted what
happened when amber was rubbed
with wool.
In 1570 English scientist William
Gilbert named it electricity after the
Greek word for amber elektron
Electrical Charge -- a concentration
of electricity. This is caused by having
either a concentration of protons
(+) or electrons (-).
Unlike Charges -- Charges which are
different -- one (+) and one (-)
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Unlike charges attract.
Like Charges -- Charges which are
the same -- Either both (+) or both (-)
Like charges repel.
**REMEMBER from our study on
atoms that objects want to be neutral.
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Current Electricity
Lightning produces light.
Is light from a light bulb produced
the same way? No!!
Lightning is caused by negative () charges in clouds that are
attracted to positive (+) on the
ground or in other clouds (static).
A light bulb needs a continuous
flow of electricity.
It takes energy to separate the
charges. You can provide
electrical energy by rubbing some
materials together. However,
electrical energy can be better
generated and stored for later use
with a battery or other item.
Current – how much electrical
charge flows past a point in a
given time is acurrent. (
– Current is measured in
Amperes (A) also known as
amps)
– Current = Charge(Q)
divided by time(t) or Q/t
Circuits
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Circuit -- A complete and closed
path through which a charge can
flow
2 types of circuits
– 1) Series circuit (any break
causes electricity to stop
flowing/ Christmas tree lights)
– 2) Parallel circuit (a break
only causes part of circuit not
to work/ most houses are
parallel)
Circuit Requirements
– a source of potential
difference ( something to
separate charges/a battery or
generator)
– a conducting path (wire)
–
resistance (something to slow
charges down or convert
electricity to another energy
form/ a light bulb heating unit or
motor).
Ohm’s Law
*I is the current,
measured in amperes
*V is the potential
difference measured in
volts
• *R is the resistance
measured in ohms
Formula for Ohm’s Law
Magnetism
Unlike poles -attract
Like poles- repel
• Magnetism is a force.
• One end of a magnet points
North & the other points South.
These 2 ends of a magnet are
called magnetic poles. (North
magnetic pole or South
magnetic pole.)
• Similar to electrical charges,
magnetic poles of 2 magnets
can have like poles & unlike
poles.
– *Like poles (2 North poles
or 2 South poles) repel.
– **Unlike poles (1 North &
1 South) attract.
***If you break a magnet into
smaller pieces, all the
pieces are a complete
magnet each with their own
North & South poles.
What causes magnetism?
• Every atom has a tiny
magnetic field around it
caused by the spinning of
electrons
• . Metallic atoms have
stronger magnetic fields
because most of their
electrons spin the same
way.
• You can align the
magnetic fields of several
atoms and create a
domain.
• *****If an object has all of
its domains in line &
working together it has
induced magnetism & is
now a magnet.
Domains of an unmagnetized object
Domains of a magnetized object
How do you make a magnet?
• Ways to align
domains or ways to
induce magnetism
– 1.Introduce object to
an existing magnetic
field. (Rub it on a
magnet).
– 2.Run an electrical
current through it.
– 3. Heat it. (Rare)
– 4. Strike it so as to
align domains. (Very
rare)
Magnetism History
• Lodestone =
Magnetite – a
naturally found
magnetic rock named
after Magnesia a
region of Europe
(Greece) the rock was
found in.
• Magnets were
originally associated
with sorcery.
• Many still believe in
their healing ability.
Magnetic Fields
• A magnetic field is a
region around a magnet
in which a magnetic force
acts.
• The Earth has a magnetic
field around it called the
magnetosphere with
layers that keep out
radiation called the Van
Allen radiation belts.
The magnetosphere is
caused by the Earth’s
core being made of iron &
nickel.
Above: A magnetic field shown with iron
filings around a bar magnet
Below: the magnetosphere
Electromagnetism
Current (I) through a wire produces a
magnetic field (B). The field is oriented
according to the right-hand rule.
• Electromagnet- a
magnet produced by
passing a current
through a coil of wire
wrapped around a
metal core.
• Electromagnets can
be turned on & off,
but are usually
stronger than
permanent magnets.
Effects of Magnets on Electricity
• A magnetic field has no
effect on a static charge,
but it does exert a force
on the wire that carries a
current. The force is at a
right angle (900) to the
direction of the current
flow.
• ******The right hand rule
lets you see the
relationship between the
current flow and the
magnetic force.
Effects of Magnets on Electricity
(cont.)
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Electric motors – uses
electromagnets to spin a material
that changes electrical energy to
mechanical energy (kinetic energy
of moving machine parts.)
– A commutator is a magnetic
device that reverses the flow
of electricit9y in a motor
causing the motor to spin.
Induced current- an electrical
current produced by using a
magnet. (Don’t confuse this with
induced magnetism).
Faraday's Magnet Induced Current
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Electrical generator – a device
that changes kinetic mechanical
energy to electricity. It uses
magnets to rotate a coil in a
magnetic field. (the opposite of a
motor)
Just for Fun
• Thor (Electricity)
Versus Magneto
(Magnetism)