Earth's Magnetic Field
EQUIPMENT
|
|
INCLUDED: |
|
|
1 |
Magnetic Field Sensor |
CI-6520A |
|
1 |
Zero Gauss Chamber |
EM-8652 |
|
1 |
Rotary Motion Sensor |
CI-6538 |
|
1 |
Dip Needle |
SF-8619 |
|
1 |
Universal Table Clamp |
ME-9376B |
|
1 |
45 cm Stainless (non-magnetic) Steel Rod |
ME-8736 |
|
1 |
Adjustable Angle Clamp |
ME-8744 |
|
| ||
|
NOT INCLUDED, BUT REQUIRED: | ||
|
1 |
ScienceWorkshop 500 or 750 Interface |
|
|
1 |
DataStudio Software |
|
INTRODUCTION
The magnitude and direction of the Earth's magnetic field are measured using a Magnetic Field Sensor mounted on a Rotary Motion Sensor. The Magnetic Field Sensor is rotated through 360 degrees by rotating the Rotary Motion Sensor pulley by hand. The Magnetic Field Sensor is zeroed using the Zero Gauss Chamber, the walls of which are made of a highly permeable material which redirects the magnetic field around the chamber.
THEORY
The magnitude of the Earth's field varies over the surface of the Earth. The horizontal component of the Earth's magnetic field points toward North (magnetic South). The north end of a compass needle is attracted to the south end of the Earth's magnetic field. So the pole which is referred to as "North" is actually a south magnetic pole.
|
BHorizontal |
|
BVertical |
|
BTotal |
|
θ |
Figure 1: Components of the Magnetic Field (Northern Hemisphere)
SETUP
NOTE: During this experiment, keep the apparatus away from all sources of magnetic fields (electrical, computers, computer interface, bar magnets). Also keep away from all ferromagnetic materials (iron, steel chairs and tables).
1. Attach the Adjustable Angle Clamp to the Rotary Motion Sensor.
2. Use the provided nonmagnetic stainless steel rod in the table clamp. The table clamp is mostly aluminum.
3. Attach the Rotary Motion Sensor to the support rod.
4. Screw the handle onto the Magnetic Field Sensor.
5. Align the key in the hollow handle with the slot on the Rotary Motion Sensor shaft and slide the Magnetic Field Sensor onto the Rotary Motion Sensor shaft (see Figure 2). Put the pulley on the side of the Rotary Motion Sensor that is opposite to the Magnetic Field Sensor. This pulley will be used to rotate the Magnetic Field Sensor by hand. Put the o-ring on the largest step of the pulley.
Figure 2: Complete Setup
6. Slide the Angle Indicator onto the end of the Rotary Motion Sensor, orienting it away from the Magnetic Field Sensor so it won't be in the way when the Magnetic Field Sensor is rotated. Remove the screw and nut from the Angle Indicator because they are ferromagnetic and will interfere with this experiment.
7. Plug the Rotary Motion Sensor into Channels 1 and 2 on the ScienceWorkshop 500 interface.
8. Plug the Magnetic Field Sensor into Channel A on the interface. Set the sensor's gain switch to x100. Set the sensor's direction switch on axial to measure the magnetic field aligned with the sensor probe.
9. Open the DataStudio file called "Earth Mag Field".
PROCEDURE
Horizontal Component of the Magnetic Field of the Earth
1. To allow the Magnetic Field Sensor to rotate in a horizontal circle, adjust the Rotary Motion Sensor clamp so the angle indicator reads 90 degrees with the Magnetic Field Sensor on top.
2. Put the Dip Needle in its horizontal orientation and position the Dip Needle directly below the Rotary Motion Sensor. Align the case of the Rotary Motion Sensor with the compass needle. Use the Rotary Motion Sensor case as a reference to the general direction of the Earth's magnetic field. Remove the Dip Needle so its magnetic field won't interfere with the experiment.
3. Rotate the Magnetic Field Sensor so the length of the probe is perpendicular to the direction of the Earth's field as indicated by the Rotary Motion Sensor case. Slip the Zero Gauss Chamber over the Magnetic Field Sensor probe and press the tare button on top of the Magnetic Field Sensor. This will ensure that the maximum on the Magnetic Field Sensor will not be exceeded during the experiment.
4. With the Magnetic Field Sensor still aligned as in Part 3, click on START in DataStudio. Slowly and steadily rotate the Rotary Motion Sensor pulley through 360 degrees. Be sure to rotate in the direction which gives positive angles. DataStudio will automatically stop when 360 degrees is reached.
5. To eliminate magnetic noise from electrical circuits, enter a smoothing factor (try 8) into the DataStudio calculator. For example: B = smooth(8,smooth(8,x)). Click on Accept. You should see the graph update with smoother data.
6. Examine the graph of the magnetic field strength versus angle. At what angle from the starting position is the magnetic field maximum? Does this approximately correspond to the direction of the Earth's field as shown by the compass needle?
7. Which direction is North (magnetic South)? Remember the magnetic field reads positive when the field points into the end of the sensor. Does the compass needle point in the same direction indicated by the magnetic field maximum?
8. Use the Smart Cursor to measure from the peak to the trough and determine the maximum value of the horizontal component of the magnetic field.
Total Magnetic Field of the Earth
1. To allow the Magnetic Field Sensor to rotate in a vertical circle, adjust the Rotary Motion Sensor clamp so the angle indicator reads zero degrees. Keep the Rotary Motion Sensor aligned with the Earth's field as shown by the compass needle (Dip Needle).
2. Point the Magnetic Field Sensor probe horizontally.
3. Put the end of the Magnetic Field Sensor all the way into the Zero Gauss Chamber and press the tare button on the Magnetic Field Sensor.
4. With the Magnetic Field Sensor still horizontal, click on START in DataStudio. Slowly and steadily rotate the Rotary Motion Sensor pulley through 360 degrees and until the program automatically stops recording data.
5. To eliminate magnetic noise from electrical circuits, enter a smoothing factor (try 8) into the DataStudio calculator. For example: B = smooth(8,smooth(8,x)). Click on Accept. You should see the graph update with smoother data.
6. Use the Smart Cursor to measure from the peak to the trough and determine the maximum value of the total magnetic field.
The Dip Angle
1. Use the horizontal component and the total magnetic field to calculate the dip angle.
2. Examine the graph of the magnetic field strength versus angle made when the Magnetic Field Sensor was rotated in the vertical plane. At what angle from horizontal is the magnetic field maximum and negative? This is the dip angle. Is this angle above or below horizontal? Why? How does your location on the Earth affect this?
就是这篇 急求啊 希望整体布局不要变化。语句基本通顺。