Lab 5_ Earth's Magnetic Field (Emma Born).docx.pdf

105 points total Name: Emma Born Lab Section: EPS 50: Fall 2022 LAB 5: EARTH’S MAGNETIC FIELD Due one week from today at the start of your lab section Introduction The Earth's magnetic field is one of the most important properties of this planet. Studies in the 1960s 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 cosmic radiation from space. 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 and effects of Earth's magnetic field. 1. Magnetic Field Lines Magnetic fields are produced by moving charged particles. Magnetic field lines describe the structure of a magnetic field in three dimensions. If we place an ideal compass needle free to turn in any direction (unlike the usual compass needle, which stays horizontal) on any point on a magnetic field line, then the needle will always point along that 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 (which approximates a dipole), field lines spread out from one pole and converge towards the other. In other words, the field lines are closest together at the poles, where the magnetic force is strongest. This is very similar to the behavior of field lines in the Earth's magnetic field. Magnetic field lines: ● never cross. ● point from the North to the South magnetic poles. ● must always connect in continuous loops (no magnetic monopoles). ● are closer together where the magnetic field is stronger.

1) Place your compass in the bar magnet’s magnetic field in each spot indicated by the circles below. In each circle, draw an arrow showing where the north arrow on the compass is pointing (showing the field direction) (12 pts) With a group, get a bar magnet, a sheet of paper, iron filings, and a compass. Place the paper over the bar magnet and carefully sprinkle the iron filings on the paper (near the magnet) until a distinct pattern emerges. The iron filings should align with the magnetic field. 2) In the space below: a) Draw the orientation of the magnet (label N-S) and iron filings (4 pts) b) Draw magnetic field lines, showing the field direction with arrowheads (5 pts) 2

3) Where along the bar magnet is the magnetic field strongest? (It may be helpful to refer to your sketch in Question 2) (3 pts) The magnetic field is strongest at the dipoles. We know this because there is a higher density of filings (and thus a higher density of magnetic field lines) at the poles. Align the north end of a bar magnet a few cm from the south end of another bar magnet. Place a piece of paper over the two magnets and sprinkle iron filings in the region between the magnets. 4) In the space below: a) Draw the orientation of the magnets (label N-S) and iron filings (4 pts) b) Draw and add arrowheads to field lines between the magnets, showing the direction of the magnetic field (confirm with your compass) (5 pts) 5) What would ideal field lines look like INSIDE a bar magnet (i.e., in which direction do they point)? Draw a bar magnet (N-S) and magnetic field lines outside AND inside the magnet, labeling with arrows to show the field direction. (3 pts) 3

2. Earth's Magnetic Field Earth’s magnetic field, shown as if a giant bar magnet were placed at the Earth’s center and slightly inclined (11°) from Earth’s rotation axis. A magnetic dipole field is the field produced by a north magnetic pole and a south magnetic pole in close proximity. The above figure shows an idealized dipole field for Earth. The magnetic field lines show the direction of the magnetic field and presently point to the north magnetic pole. There is something surprising about this fictitious bar magnet in Earth: Its south (negative) pole lies at Earth’s north magnetic pole , or “magnetic north.” You can see why this must be so by considering that, in the absence of any significant magnetic fields other than the Earth’s, the north end of a compass needle points toward Earth’s magnetic north, which is in the general direction of the geographic North Pole. However, the magnetic pole is not located at the same exact position as the North Pole. Declination is the angle between magnetic north (the 4

direction in which a compass needle points) and true north (the north geographic pole). It is often noted on maps, and also changes in space and time depending on where magnetic north is. The figure above shows an example of magnetic declination, showing a compass needle with an "easterly" variation from geographic north. N g is geographic or true north, N m is magnetic north, and δ is magnetic declination. 6) Illustrate a declination of 17°W on the compass below. Label geographic north ( N g ) , magnetic north ( N m ) , and the angle between them (δ). (5 pts) Magnetic Inclination In general, the magnetic field lines of Earth are not parallel with the surface of the planet (except at the equator), and dip into or out of the Earth at a certain angle based on magnetic latitude. The angle between the magnetic field and the horizontal is called inclination ( i ) , which is positive (+) when the field lines point into the ground, and negative (-) when the field lines point out of the ground. Magnetic inclination varies from 90° (perpendicular to surface) at the magnetic poles to 0° (parallel to surface) at the magnetic equator. The relationship between inclination and latitude for a magnetic dipole is given by: tan( i ) = 2tan( ϴ ) This means that for a location on an Earth with an ideal dipole field, if you know the magnetic latitude ( ϴ ) you can find the inclination (i), and vice versa. 7) Use the figure below to complete the table: a) Find the latitude of points A, B, C, D, and E by measuring the angle between 5

the magnetic equator (thick black line) and a line that connects the middle of the bar magnet to the point on the surface (A line is already sketched) (5 pts) b) Measure the magnetic inclination angle ( i ) at each point using a protractor. For a given latitude, the inclination is the angle between a line tangent (ﬂat) to the Earth’s surface and a line tangent to the field line that intersects the surface. Make sure to record the appropriate sign (+,-) for inclination (5 pts) A B C D E Latitude ( ϴ ) Measured Inclination (i x ) Theoretical Inclination (i) 6

Your preview ends here

Eager to read complete document? Join bartleby learn and gain access to the full version

Access to all documents
Unlimited textbook solutions
24/7 expert homework help