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		Compasses and Magnetic Fields
Activity HO-14B			Assigned: Day 14, Oct. 14, 1997
Open a Word file to record the answers to the questions in the following activities. Enter the names of all the members of your group in your Word file. Label it HO-14B, Compasses HO-14B Activity 1: Defining a magnetic field You can say that a magnetic field is present if you see a compass needle twist. Now determine the magnetic field around your bar magnet. Place your bar magnet off to the west side of your compass, oriented in such a way as to make the compass deflect to the east. 1) Describe your results. You define the direction of a magnetic field B at a particular location as the direction that the "north" end of a compass points to when placed at that location. At the location of

_{the compass, you have seen the direction of the earth's magnetic field Bearth. Assuming}

that the bar magnet makes a magnetic field along the axis of the magnet, draw a vector to

show the direction of the magnetic field B_magnetof your bar magnet, and another vector

to show the direction of the net magnetic field B_netat the location of the compass.

[Note: If your bar magnet is not already marked for future reference, write "N" for "north" on the
right end of the magnet (attach tape to write on if necessary), because there seems to be a magnetic
field pointing out of this end of the magnet. Mark the other end of the magnet "S" for "south."]

Turn your magnet 180 degrees.
2) How does the compass needle deflect, and what can you conclude about the direction of
the magnetic field at the S end of your magnet? Explain briefly.

Suspend your magnet from a thread or a hair, using a piece of tape, or float the magnet
on a dish or plate in water.
3) Which end points toward the north?

[Hint: compass consists simply of a magnet in the shape of a needle, mounted on a
pivot.]

HO-14BActivity 2:

Superposition of magnetic fields

• Obtain another magnet. Make sure you have labeled the north and south ends of both
  magnets.

4) Describe briefly the interactions that the two magnets have with each other.