Download Magnetic Fields

Lesson Plan 1 --- Magnetic Field
By Fengfeng Zhou
Objectives:
1. Refresh and reinforce students’ understanding about “Fields”. They will
understand that a field, such as magnetic field, is a special type of matter though it
is invisible. They will know that there is a magnetic field around any currentcarrying conductors.
2. Students will be able to use right-hand rules to determine the direction of
magnetic fields generated by a current-bearing wire and the polarity of a solenoid
bearing current.
3. Students will be able to understand the microscopic picture of magnetic materials.
4. Students will be able to determine how to increase the strength of an
electromagnet and exemplify the extensive use of electromagnet.
Activities:
1. Mention that a magnet has two poles, that like poles repel while unlike poles
attract. Ask students why two magnets can repel or attract each other without
contact. Tell them it is because of magnetic fields generated by the two magnets.
One magnet exerts a force on the other through magnetic fields. The two fields
are in contact. This is like the situation in which two people want to push or pull
each other in a distance. They can achieve their objective by using a tool such as
a rod.
2. Tell students that magnetic fields, like other fields such as electric fields, are a
special type of matter. Tell them that a magnetic field has magnetic energy so
that it may be able to push or pull another magnetic field.
3. Guide students to do a test to determine the direction of the magnetic field
generated by an aluminum stick. The stick is set up in vertical position. Connect
it with a power supply to form a circuit. Put several compasses around the stick.
The compasses will show the direction of the magnetic field generated by the
current when the power supply is turned on.
4. Introduce the first right-hand rule. Project a graph on the screen to illustrate how
to use the rule. Ask students to check if what they observed is consistent with the
rule. Ask them to repeat the test but change the direction of the current. Again,
ask them to compare what they observed is consistent with the rule.
5. Project a graph showing the similarity of magnetic fields generated by a bar
magnet and a solenoid carrying current. Tell students a current-carrying solenoid
can be used as a magnet called electromagnet. An electromagnet is a temporary
magnet so it can be turned on or off. Project another graph to show how to use
the second right-hand rule to determine the polarity of a current-bearing solenoid.
6. Tell students that electromagnets are extensively used. Ask students to give
examples of the use of electromagnets. Present several slides to show
applications of electromagnet which students may not know.
7. Guide students to do another test about what makes an electromagnet generate
stronger magnetic field. Students are given two solenoids with different number
of wraps. They will first notice that a steel rod put inside of a current-bearing
solenoid can tremendously increase the strength of the field. They will then
notice that increase of the current in the solenoid will make the electromagnet
stronger. They will finally notice that the solenoid with a larger number of wraps
can generate a stronger magnetic field than the other solenoid can do.
8. Return to the graph showing the similarity of two magnetic fields generated by a
bar magnet and a solenoid carrying current. Ask students why the two fields are
so similar. Tell them there must be some current loops within the bar magnet
since we know that the field generated by the solenoid is actually caused by
current loops. Tell students that there are different explanations for the current
loops within a bar magnet and magnetic materials. One explanation is that the
current loops are the result of electrons orbiting the nuclei. Some materials such
as iron, cobalt, and nickel show magnetic property because the current loops in
these materials are aligned or can be aligned.