Callibrate a Hall Probe: Planning

    n = no. of electrons per unit volume (e/m3)

                                            e = electron charge (1.6 x 10-19 C)

                                            d = thickness of film in Hall probe (m)

Formula 2

Diagram of Apparatus for calibration

Draw diagram here

Method of calibration

1. Place the Hall probe in an area with no magnets and zero it.
2. Set up Helmholtz coils as above. The current going through each coil should be 0.5A.
3. Use a wooden ruler, held by wooden clamps, positioned behind and beside the coils to find the centre of the magnetic field.
4. Position the Hall probe in the centre so that it is perpendicular to the direction of the field.

5. Record the voltage reading from the milli-voltmeter. 
6. Use Formula 1 to find a value for the corresponding magnetic flux density.
7. Increase the current going through he Helmholtz coil to 1.0A.
8. Measure the voltage reading and use Formula 1.
9. Repeat this for coil currents of 1.5A, 2.0A and 2.5A.
10. Record values for voltage and magnetic flux density using a data logger and create an automated graph.
11. Use this graph to find the corresponding magnetic flux density for any value of voltage shown by the milli-voltmeter.

NB

• The current through the coils must not exceed 3A to avoid overheating.
• The current through the Hall probe must not exceed 0.4A.
• The Hall probe should be connected to a DC power supply so that a constant current is provided and therefore a constant temperature. This increases the reliability of the results as changes in temperature can affect the measurements.
• A milli-voltmeter increases the accuracy of the voltage readings.
• Run the positive and negative leads of the coils together so that the fields they are generating are cancelled out.
• A data logger ensures accurate results.

Predicted Results for Calibration

These results have been predicted using Formula 1 and 2.

A graph to show the relationship between voltage and magnetic flux density

This graph can be described as B = 0.6V.

The Hall probe should have its own graph with a similar function of

B = mV

where m is the gradient of the graph

This then allows the voltage readings, read from the Hall probe’s milli-voltmeter, to be used to find the corresponding magnetic flux density in question.

Investigating how the magnetic flux density mid-way between opposite poles of two permanent magnets varies with the separation of the bar magnets

Diagram of Apparatus

Method

1. Mount the magnets using wooden clamp stands. This is a non-magnetic material and therefore will not interfere with the results.
2. Use a dipneedle to find the direction of the Earth’s magnetic field in your area.
3. Place the mounted magnets perpendicular to the Earth’s field. This will mean the Earth’s field is parallel to the Hall probe when it is taking readings, meaning the effect of the background field will be minimised.
4. Separate the two bar magnets by a distance of 0.01m using a vernier caliper, which would give accurate measurements of distance.
5. Use a wooden ruler, held by wooden clamp stands, positioned behind the mounted magnets to find the centre of the magnetic field by observation.
6. Place the calibrated Hall probe mid-way between the magnets, making sure it is perpendicular to the field.
7. Read the voltage and use the graph created during calibration to work out the magnetic flux density.
8. Increase the distance between the magnets to 0.02m.
9. Read the voltage and use the graph to find the magnetic flux density.
10. Take readings for distances of 0.01m, 0.02m, 0.03m, 0.04m, 0.05m and 0.06m.
11. Record the results of magnetic flux density and create a graph of distance between magnets against magnetic flux density to find a relationship, which should follow the inverse square law.

NB

• Ensure that this experiment is performed away from other magnetic materials so that results are not affected.

References

• http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/helmholtz.html
• http://physicslabs.phys.cwru.edu/EM/Manual/pdf_version/MAG.pdf
• A-Level Physics 4th Edition by Roger Muncaster – Chapter 41, Pg 615
• A-Level Physics 4th Edition by Roger Muncaster – Chapter 41, Pg 637

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