Earth s Magnetic Field

Transcription

1 April 20, 2014

2 1 Outline Acknowledgments 2 Introduction Geomagnetism Geographic vs Magnetic Poles Composition of Earth s Interior Dynamo Effect 3 Measuring in the lab Theory Former Apparatus New Apparatus (α phase) Operation Issues with α phase New Apparatus (β phase) 4 Applications of Simulating the Geomagnetic Field 5 References

3 Acknowledgments Ongoing project since spring 2013 Eric Dietz, Xueli Zou - advising, experimentation/data collection, troubleshooting, authoring papers/posters Jaydie Lee - design and fabrication Mary Murphy-Waldorf - acquiring parts and materials Robert Blanton, Chris Kaneshiro, Lynda Klein, Stephen Sun - assistance with the experiment, papers/posters

4 Geomagnetism The earth produces a magnetic field oriented roughly along its axis of rotation Originates due to phenomena in the inner and outer cores which are not well understood Related to earth s rotation Varies with time Reverses direction every 200,000 or so years

5 Geographic vs Magnetic Poles

6 Composition of Earth s Interior

7 Dynamo Effect Heat generated in the earth s outer core produces convection currents in the molten metal Coriolis effect - helical flow patterns Metal moving through the earth s magnetic field induces eddy currents in the metal Eddy currents produce a magnetic field But how did it start?

8 Theory Faraday s Law: ε = N dφ dt For the coil: Φ = B A ε ind = NB A ω sin ωt = B A cos ωt Induced voltage is directly proportional to the incident magnetic field and the angular velocity ε peak = NB A ω

9 Former Apparatus Experiment at Chico State used a custom-built coil and rotating axis Designed, tested, and written up by Kagan1 Electric motor drives rotating axis, commutator provides electrical connections Orient coil to isolate horizontal and vertical components of field Voltage observed on oscilloscope Unsupported, exposed rotating coil

10 New Apparatus (α phase) Construct a new apparatus to replace the old one Rotation driven by a hanging mass that spins a pulley Only steel on frame is the bearings More lightweight, compact, resilient and economical Data Acquisition Voltage is amplified and tracked using a LabPro/LoggerPro configuration

11 New Apparatus - Operation Frame is fixed to a rigid surface String is wrapped around pulley, free end attached to hanging mass Voltage is tracked using a data acquisition system When hanging mass is released, spinning coil accelerates from rest and generates an oscillating voltage

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14 Issues with α phase Rigidity, clamping to a rigid surface Vibration Electrical noise - grounding, brushes

15 New Apparatus (β phase) Apparatus redesigned to improve operation and facilitate in-house fabrication Polycarbonate frame, 3D printed rotating axis components Nylon fasteners on frame and rotating axis, brass sleeves for electrical contact Rotation sensor replaced by standalone pulley Only steel on frame is the bearings Enclosed frame is more rigid, better at protecting coil from damage

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17 Simulating the Geomagnetic Field Gary Glatzmaier of Los Alamos National Laboratory and Paul Roberts of UCLA 2 Solid inner core, fluid outer core, gravitational coupling between the inner core and mantle, convection, field generation, heat flow, material properties Sperical harmonic and Chebyshev polynomials solved in increments of 15 days Results produce a similar drift of the field and reversal period as per experiment

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21 Thanks for listening! Questions?

22 References 1 D. Kagan. Measuring the in an Introductory Laboratory with a Spinning Coil. In The Physics Teacher, Oct. 1986, G. Glatzmaier. Geodynamo. Accessed 14 Apr ucsc.edu/~glatz/geodynamo.html