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Chapter 36 Magnetism: Magnetic Fields & Domains
When were the first
magnets discovered?
What were they made of?
How was the connection
made that magnetism and
electricity were
interconnected?
How are magnetic forces
similar to electrical
forces?
Magnetic rock was discovered over 2000 yrs ago in Magnesia, Greece.
Lodestone (magnetite)
In 1820 Hans Christian Oersted, a Danish science professor, discovered
that electricity affected the needle of a compass during a demonstration
to his class.
Force is both attractive and repulsive.
The force decreases with an increase distance of separation.
Describe the behavior of
magnetic poles.
There is a North seeking pole & South seeking pole
Opposites attract, like repel.
Magnetic poles cannot be isolated like electric charges. A north pole
cannon exist without a south pole
What is a magnetic field?
The space around a magnet where a magnetic force is exerted.
How can electricity
produce a magnetic field?
What produces the field
in a magnet?
How can this field be
made stronger?
Why are most substances
not magnetic?
Why does iron have a
strong tendency to
become magnetized?
A moving charge produces a magnetic field
What are magnetic
domains?
In a magnet, the field is produced by the motion and spin of the electrons
Many electrons spinning in the same direction produces a stronger
magnet
Electrons spinning in opposite directions cancel each other. This is why
most substances are not magnetic
With iron, each individual atom creates a magnetic field. Iron has 4
electrons in its outer shell with the same spin.
Clusters of aligned atoms are called magnetic domains. All Iron has
magnetic domains. When all the domains align the iron becomes
magnetized
What do electric charges have in common with magnetic poles? How do they differ?
Summary
They are similar because they are both are attractive and repulsive forces and
that force will change with a change in distance, but they differ in that while a
proton and an electron can be isolated in an electric current, you cannot isolate
the north and south pole of a magnet because they are created by the spin of the
electrons within the atom.
Chapter 36 Magnetism: Electromagnets
What happens to a magnetic
field when a current
carrying wire is looped?
If a wire carrying the charge is bent into a loop the magnetic field
becomes bunched up inside.
What happens as the
number of loops is
increased?
1 loop concentrates the field 2 loops double the concentration, 3 loops
triple it.
What is an electromagnet?
What are some applications
for electromagnets?
A current carrying wire with many loops is called an electromagnet.
Electromagnetic trains & rails, Industrial magnets such as the type used
in junkyards, speakers for converting electric impulses into sound waves,
and electric motors.
Chapter 36 Magnetism: Magnetic Forces
How does a magnetic
field affect a stationary
charged particle?
How does a magnetic
field affect a moving
charged particle?
If a charged particle is not moving, a magnetic field has no effect on it.
If a charged particle is moving through a magnetic the particle will be
deflected.
When is the force the
greatest?
When is it at zero?
Force is greatest when the particle moves perpendicular to the field.
The force is zero when it moves parallel.
What is the result of this
effect on the Earth’s
magnetic field?
This same interaction protects the Earth from cosmic radiation
What happens when the
charged particle is trapped
inside a wire?
If the charged particle is trapped inside the wire then the entire wire will
respond to the deflecting force.
What are some of the
applications to this effect?
Galvanometer: A current measuring device. These can be calibrated to
measure voltage or amperes.
You can also modify the design to make a motor
What is one possible
reason for the Earth’s
magnetic field?
Convection currents in the earth’s outer core may be the reason for this.
Describe the stability of
the Earth’s magnetic field
The Earth’s magnetic field is not stable. It has in the past change
directions about every 500,000 to 1 million years. The Last change was
700,000 years ago. There has been a 5% decrease in the strength of the
field in the last 100 years. Scientists believe that a reversal may happen
in the next 2000 years.
A magnetic field can deflect a beam of electrons but it cannot do work on them to speed them up. Why?
Hint: consider direction of force
Summary
There is no component of the magnetic force in the direction of the movement of
the electron. The force is perpendicular.