University of Virginia
Physics Department

## The Magnetic Field

A Physical Science Activity

### Student Activity

Materials

• CBL System
• TI-83 Graphing Calculator (with PHYSCI programs)
• Vernier Magnetic Field Sensor
• Meter stick
• Bar magnet
• Clear tape
• Ring stand
• Utility clamp

Procedure

1. Tape the meter stick to the top of the table so that it doesn't move easily.
2. Set up the stand and clamp so that the magnetic field sensor end is at the 0 marker on the ruler. The small white spot on the end of the sensor should be facing the magnet.
3. Connect the Vernier magnetic field sensor to the adapter cable and then into the CBL unit in CH 1. Link the CBL unit and the TI graphing calculator by connecting the black link cable into the bottom of both the CBL unit and the calculator.
4. Prepare the CBL / sensor / calculator for data collection by entering into the PHYSICS program and setting up the magnetic field probe. Select SETUP PROBES, then ONE probe. To set the type of probe, select MORE and then under the new menu choose MAGNETIC FIELD. Use the USE STORED in the calibration menu. Select LOW (GAUSS) from the magnetic field setting menu and make sure that the detector's switch is set to LOW.
5. Select ZERO PROBES from this menu, CHANNEL 1 and then press TRIGGER on the CBL to set the zero of the probe.
6. From the main menu, select COLLECT DATA and use the TRIGGER/PROMPT feature. This will allow you to move the magnet, record a reading, then enter in how far away it was.
7. Start by placing the magnet 4-cm away from the magnetic field sensor by placing it on the ruler. Find the orientation of the magnet that gives the highest field reading. This will mean the polarization is along the meter stick. Rotate the magnet along the meter stick so that the pole facing the sensor gives a positive reading. After each measurement select MORE DATA and then slide the magnet back 2 cm and take the new measurement. When prompted for data entry on the calculator, enter in the correct distance for each measurement you take.
8. Select STOP and GRAPH from the menu to see a plot of magnetic field vs. distance. Draw the plot that you see on the calculator screen after you have finished collecting data.
1. Disconnect the calculator from the CBL unit while the graph is displayed on the screen of the calculator.
2. Connect the gray TI-Graph Link Cable to the computer's serial port and then to the calculator's link port at the base of the calculator.
3. Start the TI-Graph Link Software and select LINK from the menu at the top of the screen.
4. Choose GET SCREEN from the drop down menu and then when the box comes up choose GET SCREEN again.
5. Select PRINT.
6. Reconnect the TI calculator to the CBL unit.
10. Fill in the data table by using the left and right arrow buttons to trace from point to point along the graph. Read the magnetic field for each point from the bottom of the screen.

Data Sheet

 Distance (cm) 4 6 8 10 12 14 Magnetic Field (Gauss)

Questions:

1. What happens to the magnetic field strength as distance increases?

2. What would the magnetic field strength be at 7 cm?

3. What would the magnetic field strength be at 16 cm?

4. How does this help explain why the magnetic field of the earth does not overpower the magnetic field of the bar magnet when we hold a compass to it?