Download Laboratory 3

EGN 100 Introduction to Engineering
Magnetic Fields Lab
In magnetism, direction is defined by naming one pole of a magnet the north pole and the other
the south pole. The magnetic field of the earth was known in early times, in that a magnetite (a
mineral, naturally occurring material) needle floating on water would line up in a north-south
direction. A compass is a simple tool that can be used to determine the direction of a magnetic
field. The compass needle points in the direction of the field. See
http://www.howstuffworks.com/compass.htm .
Observe carefully and record all observations.
Part A
With the magnet and compass on the table as shown, explore
around the magnet with the center of the compass about 4
centimeters (1.5 inches) away from the magnet. Do not bring the
compass close to the magnet. How does the direction of the of the
compass needle change as you explore? When done, place the
magnet a few feet away so it doesn’t interfere with the next
experiment. What conclusions do you draw regarding the
direction of the magnetic field around a bar magnet?
Part B
We will use the power supply as a current supply. Set the voltage of the power supply to 1 volt.
Turn the current limit down to as low as it goes. Place the wooden wire support so the wire is
horizontal. Connect the end of the wire with a dot on the post to the positive terminal of the
power supply. Connect the other end of the wire to the negative terminal. Adjust the current to
about 2 amperes. Disconnect the wire from the positive terminal. Consider positive current to
come out of the positive terminal. Sketch the apparatus and the direction positive current flows
through the wire.
Line up the compass and the wire so that the wire is oriented
in a north-south direction, with the dotted post in the south
direction. The compass should be on or slightly above the
wire and midway between the wooden posts. The needle
should be pointing in the direction of the wire. Keep the
compass horizontal at all times so that the needle can rotate
freely. Connect the wire to the positive terminal and record
the direction of the compass needle (north, south, east, west,
or something in between). Move the compass to a position
just below the wire. What is the direction of the needle?
What conclusions can you draw regarding the direction of the magnetic field produced by a
current flowing through a wire?
Part C
Turn the board so the wire is vertical. Keeping the compass
horizontal and next to the wire, move the compass around
the wire. How does the direction of the needle change?
Assume that the compass needle is lining up with magnetic
field in the space surrounding the magnet or the wire.
Sketch the magnetic field direction. Discuss your
observations. What conclusions can you draw regarding
the magnetic field produced by a current flowing
through a wire?
Part D
On the power supply, set the voltage to 1.0 volts and
reduce the current limit to its minimum setting. Connect
one end of the wire coiled around the bolt to the
negative terminal and the other end to the positive
terminal. Increase the current to about 2.0 amperes.
Explore the magnetic field around the electromagnet
with the compass 4 centimeters (1.5 inches) distant
from the electromagnet. Do not bring the compass close to the electromagnet. Record your
observations.
Keeping the electromagnet in the same position and orientation, reverse the connections
of the wires to the power supply. Explore the magnetic field around the electromagnet
and record your observations. Compare these observations with those for the first current
direction. Disconnect the wires from the power supply. What do you conclude from
these observations? Write your conclusions on a piece of paper.
Place the compass a few feet away so it will not be affected by the next experiment.
Part E
Merge two teams so you have two cylindrical magnets.
Place one magnet on the table surface with the rolling
surface on the table. Holding this first magnet in place,
gently bring a circular end of the second magnet toward
a circular end of the first. What happens? Bring the
other flat end of the second magnet toward the same
flat end of the first. What happens?
Repeat this procedure, but don’t hold the first magnet
in place. What happens?
What do you conclude from these observations?