Lab EC-6: Magnetic Fields and Forces
All space is permeated by magnetic fields. In this lab
magnetic fields are detected using the Hall Effect, about which the
students learn in class. Hall Effect probes measure one component
of a magnetic field at a time.
The magnetic field sensor currently (2/14) used in this lab is made
by Pasco Scientific. This sensor has two switches and one button:
radial/axial switch: choose "axial" to measure the component of the magnetic field perpendicular to the end of the probe, at the location of the white dot on the end of the probe. Chose "radial" to measure the magnetic field perpendicular to the side of the probe, at the location of the white dot on the side of the probe.
tare button: used to calibrate the probe (see below).
range select switch: chose "1x" to measure the magnetic field from the magnets. Choose "100x" to measure the Earth's magnetic field.
Calibration
To calibrate the probe, set the "radial/axial" switch and the "range select" switch as desired, then insert the probe into the Zero Gauss Chamber, and press the "tare" button. Repeat this process whenever you change the setting of either of the switches.
Earth's Magnetic Field
The Earth's magnetic field has a magnitude of about half a gauss and is
oriented (in Wisconsin) close to the local vertical. The students
should be able to use the magnetic field sensor to measure the
magnitude of the Earth's magnetic field to within 10%-20% and to estimate
the direction to 10-15 degrees.
The DataStudio set-up, including calibrations for the "100x"
setting of the magnetic field sensor, is here (right-click to
download).
Things to watch out for:
Students may find, as they move the probe about while attempting to measure the Earth's magnetic field, that they measure
a magnetic field varying from (for example) -0.5 gauss to -1.5
gauss. This indicates the zero level has not been properly set in
the calibration.
Question: can the students use the sensor to detect the field
created by the current through the strap in Experiment EC-6, part 2?
Magnetic Field of a Magnet
The magnets used in this experiment have surface fields on the order of
50 gauss. As one magnet is rotated, students can use the
magnetic field sensor to map out the changes in magnitude and direction
of the combined field of both magnets. They may also use the
sensor to look at the field of the permanent magnet used in the
magnetic balance.
The DataStudio set up, including calibrations for the "1x"
setting of the magnetic field sensor, is here (right-click to
download).
Things to watch out for:
Possible zero-level offset, as described above. Ask the students
to move the sensor far away from the permanent magnets. The
magnetic field should be measured as about zero gauss.
Sensor saturation. If the probe is used with a range select of "10x", then if it is moved too close to the magnets
the sensor may saturate. Students will see a flat line appear on
the graph, no matter how they move the probe. This does not appear to be
bad for the sensor, but it does indicate that the "1x" setting should be used.
Question: can the students use the sensor to locate the N and S
poles of the magnet in Experiment EC-6, part 2?