Magnets

C Block started with magnetism today, looking at the nature of magnetic fields and forces and relating that to Earth's magnetic field. You should be able to determine the direction of field lines for a magnet, know which pole arrangement generates attractive vs. repelling forces, understand that magnets always exist as dipoles and that Earth's magnetic field resembles, to a degree, that of a bar magnet. Since the north pole of a magnet points towards another magnet's south pole, the north end of a compass needle points towards Earth's magnetic south pole. Geographic north approximates magnetic south and vice versa. We discussed the variable nature of Earth's magnetic field over time and how scientists believe Earth's magnetic field is maintained. Those moving charged particles in our molten core is a nice segue-way into tomorrow's discussion of electromagnetism.

B and E Blocks conquered electromagnetism today in class. A current-carrying wire generates a magnetic field whose field lines make concentric circles around the wire. If a stronger magnet is needed, for the same current, looping the wire will suffice and the more loops/unit area, the stronger the magnetic field. Multiple loops of wire make what is called a solenoid and its magnetic field is very much like that of a bar magnet. Adding an iron core to the solenoid creates a true electromagnet, and its field strength is greatly increased over an air-core solenoid. On Monday, we'll take up the idea of how those magnetic fields make forces that interact with other pieces of wire or charged particles.

F Block conducted two laboratory investigations on magnetism. One looked at the relationship between the number of loops of wire around an iron nail and the strength of the generated magnetic field. The second looked at the properties of the magnetic field across the body of a bar magnet and at a distance from the magnetic poles. For electromagnets, the number of loops is directly related to magnet strength and your graph produced an nice linear relationship between number of winds and magnitude of magnetic field. You could use that relationship to predict how many loops you would need to create a magnet of a specific field strength and that is what a manufacturer would do at a factory. For the bar magnet, field strength increased as you approached the magnet and decreased as you moved away from the magnet. Across the body of the magnet, the field strength was highest at the poles (though of opposite signs) and decreases as we moved towards the middle of the magnet, where the direction of the field flipped. You conclusion should offer explanations for these results and the first section of Chapter 21 is a good place to look.