Name
Date
2
Laboratory
Activity
Creating Electromagnets
Class
Chapter
7
A magnetic field exists around any wire that carries an electric current. By coiling the wire
around a bolt or nail, the strength of the magnetic field will increase. A coil of wire wrapped
around a bolt or nail will become an electromagnet if the wire is connected to a battery or other
source of current. The magnetic force exerted by an electromagnet can be controlled by changing
the electric current.
Strategy
You will construct several electromagnets.
You will compare the strength of the magnetic force of four electromagnets.
You will determine the relationship between the strength of the magnetic force and the number of
turns of wire in the coil of the electromagnet.
Materials
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
iron bolts, identical, at least 5 cm long (4)
marking pen
masking tape
BBs, iron
*paper clips
small, plastic cups (2)
insulated wire
1.5-V dry cell battery
*Alternate materials
Procedure
1. Place masking tape on the heads of the
bolts and label the bolts A, B, C, and D.
2. Put all the BBs in one cup.
3. Test each bolt for magnetic properties by
attempting to pick up some of the BBs
from the cup. Record your observations in
the Data and Observations section.
4. Wrap 10 full turns of wire around bolt A.
Wrap 20 turns of wire around bolt B,
30 turns around bolt C, and 40 turns
around bolt D.
Figure 1
5. Use masking tape to connect the ends of
the wires of bolt A to the dry cell as shown
in the figure. Carefully use your electromagnet to pick up as many BBs as possible.
Hold the electromagnet with the BBs over
the empty cup and disconnect the wire to
the dry cell. Make sure all the BBs fall into
the cup. Count the number of BBs in the
cup. Record this value in the table in the
Data and Observations section.
Dry cell
BBs
Bolt
Magnetism and Its Uses
53
Name
Date
Class
Laboratory Activity 2 (continued)
Determine which axis should be labeled
Number of BBs picked up and which should
be labeled Number of turns of wire. Plot
your findings on the graph.
6. Return all the BBs to the first cup.
7. Repeat steps 5 and 6 using bolts B, C, and
D. Record in the table the number of BBs
each electromagnet picked up.
8. Use the blank graph in the Data and
Observations section to construct a graph
relating the number of BBs picked up by
the electromagnet and the number of turns
of wire in the electromagnet.
Data and Observations
Observation of the magnetic properties of the bolts alone:
Number of turns of wire
A
10
B
20
C
30
D
40
54 Magnetism and Its Uses
Number of BBs picked up
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Electromagnet
Name
Date
Class
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Laboratory Activity 2 (continued)
Questions and Conclusions
1. How is the number of BBs that were picked up related to the magnetic force?
2. How is the strength of the magnetic force exerted by an electromagnet related to the number of
turns of wire?
Magnetism and Its Uses
55
Name
Date
Class
Laboratory Activity 2 (continued)
3. Explain how your graph supports your answer to question 2.
4. Use your graph to predict how many BBs a bolt wrapped with 50 turns of wire will pick up.
5. Why is it important that the bolts used in this experiment are identical?
Strategy Check
Can you construct electromagnets of different strengths?
Can you compare the strength of the magnetic force exerted by different electromagnets?
Can you explain how the strength of the magnetic force is related to the number of turns
of wire in the coil of an electromagnet?
56 Magnetism and Its Uses
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
6. A magnetic force exists around a single loop of wire carrying an electric current. Explain why
coiling a wire around a piece of iron increases the strength of an electromagnet.