Download Notes Sec 4.1

Chapter 4
Magnetism and Electricity
4.1 MAGNETIC FORCES AND FIELDS
MAGNET: an object that can exert a pull, of force, on a piece of iron. It can
attract or repel an object without touching it.
MAGNETIC FIELD: a region in space where magnetic effects can be
detected. It is used to show how magnets exert forces on an objects. The
stronger the magnet the larger the field. The earths magnetic field is millions
of kilometers in diameter.
MAGNETIC POLES
The region on a magnet where the magnetic fields are the strongest, they are
usually on the end of each magnet.
NORTH POLE: the end of the magnet that is attracted northwards.
SOUTH POLE: the end of the magnet that is attracted southwards.
MAGNETIC LINES OF FORCE
Lines that show the magnetic field. They are always drawn from the north pole
to the south pole because this is the direction a compass needle would point
when near a magnet.
N
S
N
S
N
S
S
N
GEOMAGNETIC POLES
The places in the earths magnetic field that are the most concentrated. They
are not at the north pole or the south pole. Actually they are 1500km from the
N pole and 2600km from the S pole.
Draw figure 4.6
Label -geographic north and south pole
-geomagnetic north and south
-the bar magnet inside the earth
4.2 MAGNETS AND MAGNETISM
MAGNETIC ELEMENTS: any material that can be magnetized,
Iron, Cobalt, Nickel, and Gadolinium
CAUSES OF MAGNETISM: more atoms are aligned in one
direction than in any other direction. Therefore more electrons are
moving in one direction, so the magnetic affects do not cancel each
other out.
PROPERTIES OF MAGNETS
Can occur naturally as magnets, example: iron oxide
Every magnet has two poles
1) a north pole which is attracted to the north pole
2) a south pole which is attracted to the south pole
If 2 north poles are brought together they will repel
If 2 south poles are brought together they will repel
If a north and a south pole are brought together they will attract
MAGNETIC DOMAIN: groups of aligned atoms or electrons.
a) magnetized
b) demagnetized
PERMANENT MAGNET: materials that are able to stay
magnetized for a long time. These magnets are able to lose their
magnetism if the object is dropped or banged because this causes the
domain to become disordered.
4.3 ELECTROMAGNETISM
the magnetic field that is produced when an electric current is passed through a
magnetic material
ELECTROMAGNETS: a magnet that is only produced when an electric
current flows through the material
Used in doorbells, telephones, speakers etc;
RIGHT-HAND-RULE: used to predict the magnetic lines of force around a
current carrying wire. It states if you point your right thumb in the
direction of current flowing in the wire, the curl of your fingers will
indicate the direction of the magnetic lines of force around the wire.
Wire with current coming out
of the page
Wire with current going
into the page
ELECTROMAGNETS
There are 3 ways to increase the strength of a magnet
1. use a stronger electricity source to increase the current (bigger
battery)
2. wrap more coils of copper wire around the object
3. use a larger metal core for the magnet
4.4 ELETRIC GENERATORS
ELECTRIC GENERATORS: any device that can change electrical
energy into mechanical energy
- Generators produces electricity by moving a conductor through a
magnetic field or by changing the magnetic field surrounding the
conductor. Each procedure exerts a force on the electrons in the
conductor and results in the electrons moving through it.
A coil and magnet moving back and forth act as the generator of
electricity because the movement of the magnet, changes the
magnetic field around the coil.
GALVANOMETER: is a device that can measure currents
ALTERNATING CURRENT
-current that can flow in both directions
- it is produced in a generator and changes direction 120 times
per second
DIRECT CURRENT
- current that can only flow in one direction
- it is produced in a battery and only flows in one direction
ELECTRIC MOTORS
- electric motors change electrical energy into mechanical
energy, therefore; they are opposite to electric generators
RIGHT-HAND-RULE SELF TEST
Predict the direction of the compass needle in the following examples
1.
+
2.
_
Current coming out of the page
-
3. Current going into the page
RIGHT-HAND-RULE SELF TEST
Predict the direction of the compass needle in the following examples
1.
+
2.
Current coming out of the page
_
-
3. Current going into the page
Feb 27th, 2002
Name________________
Magnetism Quiz 1
Answer the questions in the space provided.
1. What is a magnet?
2. What are 2 materials that are naturally magnetic?
3. Draw a few lines of magnetic field around the following magnets.
S
N
S
NN
N
4. Describe what a magnetic domain would look like in a piece of magnetized material.
Feb 27th, 2002
Name________________
Magnetism Quiz 1
Answer the questions on a separate piece of paper
1. What is a magnet?
2. What are 2 materials that are naturally magnetic?
3. Draw a few lines of magnetic field around the following magnets
S
N
S
NN
N
4. Describe what a magnetic domain would look like in a piece of magnetized material.
Name________________
March 1st, 2002
Magnetism Quiz 2
Answer the questions in the space provided.
1. The current is flowing from the + to the -, using the Right-Hand-Rule, show the direction of
magnetic field on the wire.
+
-
2. Name 2 ways to increase the strength of an electromagnet.
3. What is a permanent magnet
4. Name two ways to demagnetize a magnet.
Feb 27th, 2002
Name________________
Magnetism Quiz 2
Answer the questions in the space provided.
1. The current is flowing from the + to the -, using the Right-Hand-Rule, show the direction of
magnetic field on the wire.
+
2. Name 2 ways to increase the strength of an electromagnet.
3. What is a permanent magnet?
4. Name two ways to demagnetize a magnet.
-