Lab : Magnetic Fields
(bar magnets & electromagnets)
Learning Goals
During this lab activity, you will learn to
a) Predict the direction of the magnet field at different locations around a bar magnet and an
electromagnet.
b) Compare and contrast bar magnets and electromagnets.
c) Identify the characteristics of electromagnets that are variable and what effects each variable
has on the magnetic field’s strength and direction.
d) Relate magnetic field strength to distance quantitatively and qualitatively
Procedure
1. Go To: http://phet.colorado.edu/simulations/sims.php?sim=Faradays_Electromagnetic_Lab
Hint: Download the file using the ‘save’ option then run the ‘.jar’ file using Java.
2. Complete the following tasks to help you investigate Faraday’s Electromagnet Lab. These tasks
will help you conduct appropriate experiments to answer the lab questions.
We will be using the Bar Magnet and Electromagnet tabs for this activity and the other tabs later in
the unit.
o Click on the Bar Magnet tab.
o Click on
. Explain the two changes this causes in the simulation.
o Move compass to various locations around the bar magnet. Explain what orientation the
needle takes with respect to the bar magnet.
o Select ‘Show Field Meter’
. The image below will appear. The meter can
be moved to various locations and indicates the magnetic field strength at the crosshairs.
Label: Total magnetic field, y-component of the magnetic field, x-component of the
magnetic field, angle and units in the following diagram.
o You should be able to determine the direction of the magnetic field vector using the meter.
o Select
. Observe the orientation of the small compass needles.
o Click on the Electromagnet tab.
o What is behaving like a magnet : The battery
.
or
The coils of current carrying wire ?
o Using the slider on the battery, change the voltage of the battery from 10V to 0V.
Then from 0V to ‘-’ 10V.
Record the changes you observe in the direction of the compass needle.
o Select AC as your current source.
Observe and record the changes in the compass needle.
3. With the electromagnet active, place the field sensor somewhere near the lower left corner of the
battery, approximately along the centerline of the coil.
4. Prepare to take some data that will relate the battery strength (potential) to the resulting magnetic
field strength. Make a two column table with the 1st column listing the battery potential and the 2nd
column the magnitude of the magnetic field.
Adjust the potential to 10 or values between -10V and +10V, including 0V, and record the potential
and the associated magnetic field (magnitude).
Plot the magnetic field strength (vertical axis) vs. the potential.
What do you observe about the relationship between the potential and the magnetic field?
Other Questions:
1. Explain the similarities and differences between a bar magnet and an electromagnet
2. Using Diagrams and written explanation, explain the magnetic field direction and strength
around a bar magnet and an electromagnet.
3. Identify the characteristics of electromagnets that are variable and what effects each variable
has on the magnetic field strength and direction.
4. Because you know that the battery potential causes current electrons to move in the loops of
a coil (such as in part 3 – our electromagnet), can you speculate about what causes a
magnetic field about the bar magnet and about the earth?
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