lab11 - Name: SID: Lab 11: The Earth's Magnetic Field...

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Name: SID: Lab 11: The Earth's Magnetic Field Introduction: The Earth's magnetic field is one of the most important properties of this planet. Studies in the 1960's of the earth's magnetic field and magnetic anomalies led to the discovery of plate tectonics, which is one of the most important theories about Earth's dynamics. Earth's magnetic field also shields us from most space-derived cosmic radiation. In some ways, Earth’s magnetic field behaves in the same way that magnetic fields on ordinary magnets behave. In this lab we will be exploring some of the properties of Earth's magnetic field. Objective: In the first part of this laboratory we will visualize a magnetic field by observing the alignment of iron filings around a magnet. We will then extrapolate this to Earth, which to a first approximation, has a dipole magnetic field. You will explore what a dipole field is, and how is Earth's magnetic field is similar and different from that of a dipole. We then look at how we use Earth's magnetic properties as a record of tectonics and geologic time. Answers: Please answer the indented, numbered questions on the answer sheet at the back of the lab handout. Explanations should be concise; most questions can be answered with a few words, or a sentence or two. All answers should be your own, but we encourage you to discuss and check your answers with 2-3 other students. Discussion and explanation are terrific ways to learn! Labs are graded out of 100 points, and then scaled accordingly. -------------------------------------------------------------------------------------------------------------- Part 1: Magnetic Field Lines Magnetic fields are produced by moving charges. Tracers of these fields are called “magnetic field lines;” they describe the structure of magnetic fields in three dimensions, and are defined (rather abstractly) as follows. If at any point on such a line we place an ideal compass needle, free to turn in any direction (unlike the usual compass needle, which stays horizontal), then the needle will always point along the field line. Field lines converge where the magnetic force is strong, and spread out where it is weak. For instance, in a compact bar magnet or "dipole," field lines spread out from one pole and converge towards the other. The magnetic force is strongest near the poles where they come together. The behavior of field lines in the Earth's magnetic field is very similar. With a group, get a bar magnet, some plastic wrap, iron fillings and a compass. Place one of your bar magnets on a piece of loose-leaf paper. Place the plastic over the magnet (this is so that the iron fillings do not stick directly to the magnet!). Sprinkle the iron filings from a height of about 10 cm. Continue sprinkling until a distinct pattern emerges. The iron filings fall on the plastic and align themselves with the magnetic field.
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1) Draw a simplified version of the field pattern that emerged when the iron filings were placed on the bar magnet. Be sure to show the shape of the field. What is the most unique
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This note was uploaded on 09/17/2009 for the course EPS 50 taught by Professor Staff during the Spring '08 term at University of California, Berkeley.

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lab11 - Name: SID: Lab 11: The Earth's Magnetic Field...

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