Electromagnets

Tanya English O'Keeffe Elementary School
6940 South Merrill Avenue
Chicago IL 60649
(312) 535-0600

Objectives:

The students will make an electromagnet that will attract a metal object.

The students will increase the strength of an electromagnet so that it will
attract an increased number of metal objects.

The students will compare the properties of magnets and electromagnets.

Materials Needed:

For 20 students.

10--20 inch strips of insulated copper wire, 1/2 exposed on each end
10--40 inch strips of insulated copper wire, 1/2 exposed on each end
15--size "D" batteries
1--battery holder for 2 "D" batteries
10--compasses
25--iron nails, 4" long
1--box of paper clips, approx. 300
iron filings
5" x 7" index card or clear transparency

Strategies/Activities:

Activity #1:
Give each pair of students one battery, iron nail, 40" copper wire, and about 30
paper clips. Have them, using only the nail, try to pick up as many paper clips
as possible. Discuss methods and results. Then instruct them to wrap the
copper wire around the nail ten times leaving 5-6 inches of wire free on each
end of the nail. Attach one end of the wire to the negative pole of the
battery. Tape securely and then touch the other end of the wire to the positive
pole of the battery while their partner uses the nail to pick up paper clips.
Then release the wire from the positive pole of the battery. Discuss methods
and results. Record the number of paper clips picked up by the magnetized nail
by each group.

Concept: Electric current flowing through a wire creates a magnetic field which
caused the iron nail to become a temporary magnet. When the electric current is
cut off, the nails loses its magnetic property and the paper clips fall off.

Activity #2:
Elicit ideas and suggestions from students on how they can make the nail pick up
more paper clips. Possible ideas are to: 1) use more wire; 2) use more
batteries; 3) use more nails. Break students into groups of four and let one
group test the idea of using more batteries; another group using 2-3 nails; a
third group using more wire, wrapping the nail 15-20 times; and another group
wrapping the nail 30-40 times. Reconnect the circuit and pick up as many nails
as possible. Record the results of each group and discuss results.

Concepts: The strength of an electromagnet can be increased by using more
batteries and/or more wires. Using more nails will increase the electromagnet's
capacity to hold more paper clips, without necessarily increasing the magnetic
force.

Activity #3:
Have students work in pairs. Give each student a 20" length of wire and a
compass in addition to their battery. Have them secure one end of the copper
wire to the negative pole of the battery. Have their partner hold the looped
center of the wire over the compass and they are to observe what happens to the
compass needle when the other end of the wire makes contact with the positive
pole of the battery. Repeat this process, but with a slight variation: attach
the wire to the positive pole of the battery first, then, holding the looped end
of the wire over the compass, complete the circuit touching the other end of the
wire to the negative pole of the battery. Observe how the compass needle
reacts. Discuss observations. Repeat if necessary.

Concept: Electromagnets have poles which can be reversed when the path of
electricity is reversed. This is not a characteristic of regular magnets.

Activity #4:
This is a teacher demonstration in which the students will observe what happens
when iron filings are sprinkled over an electromagnet. Place two batteries in a
battery holder and connect the end wires to the end wires of an electromagnet
(nail wrapped with copper wire). Place them on the overhead projector and place
the clear transparency over the electromagnet. Slowly sprinkle iron filings
over the transparency and observe what happens to the iron filings. Discuss
observations.

Concept: Electromagnets have lines of force.

Assessments:

At the conclusion of the mini-teach, the students will be able to answer thee
following questions:

Name 3 ways in which magnets and electromagnets are alike.
(Have poles, attract metals, have lines of force)

Name 3 ways electromagnets differ from magnets.
(Electromagnets need electricity to work, the poles of electromagnets can be
reversed, the strength of electromagnets can be increased)

List 2 ways to increase the strength of electromagnets.
(more batteries, more wire)

References:

Physical Science Activities for Grades 2-8, Science Curriculum Activities Library Tolman, Marvin N. and Morton, James O. Parker Publishing Company, Inc. West Nyack, NY, 1986 Magnetism and Electricity Koch, Dallas Milliken Publishing Co., 1985