PhysicsLAB: Magnetic Field in a Solenoid

In this lab we will investigate the magnetic field with a metal slinky with the use of a Hall probe. At the end of the experiment we will be able to calculate an experimental value for µ_o, the permeability of free space.

Materials

1 power supply
1 metal slinky – stretch to about 120 cm.
2 ring stands
4 test tube clamps
1 LabPro
1 magnetic sensor – with box and tape
1 voltage sensor
7 wires with alligator clips
3 wires with red banana clips
1 wire with black banana clips
1 switch
1 ammeter – set to 20 amps, DC

Adobe Illustrator image provided courtesy of S. Buck, 2007

Procedure

After setting up the apparatus, measure the length of your solenoid and count the number of coils. Make sure that the magnetic field probe is as close to the center of the slinky as possible.
Start Logger Pro (Start > Programs > Math > Logger Pro 3.1) and verify that the LabPro is collecting data for voltage and magnetic field strength. Make sure that the white dot on the magnetic probe is facing towards the end of the slinky which is connected to the negative wire from the power supply.
Once you know that Logger Pro is working, turn the power supply (to 0-24 DC volts), adjust the voltage to approximately 0.75 volts, and close the switch. Adjust the voltage on the power supply until your ammeter reads approximately 0.1 amps.
Record current (ammeter output), voltage (Logger Pro graph), and magnetic field strength (Logger Pro graph) in the table below. By increasing the current by 0.1 amps, repeat the experiment 15 times until you reach a maximum of 1.5 amps.
Turn off your power supply and clean up your apparatus before beginning your analysis.

Data

What was the stretched length (m) of your slinky during this experiment?

Through how many coils was the electric current flowing? Be sure to include both the first and last coils where you attached the leads from the power supply.

Trial	Voltage (volts)	Current (amps)	Magnetic Field (mT)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15

Conclusions

Open the file 1-MagneticSlinky.xls on the file system and save your data as LastnameLastnameMagneticSlinky.xls in your period folder. Once the file is saved, enter your data.

What is the filename of your group's EXCEL graph?

To three significant digits, what is the slope of your graph's line of best fit?

Using the slope of your line along with the length of the solenoid and the number of coils calculate your group's experimental value for µ_o, the permeability of free space. Show your work on your graph or on an accompanying paper.

Knowing that µ_o = 4π x 10^-7 Tm/A, calculate a percent error for your experiment. Show your work on your graph or on an accompanying paper.

Do you think that placing the magnetic sensor probe at either end of the slinky would have affected your result? Explain why or why not.

Program your EXCEL file to use your data for voltage and current to calculate the resistance of the slinky. What was your experiment's average value in ohms?

After completing your submission, make sure that you turn in a printout of your data tables, your calculations, and your EXCEL graph.