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Journal 4/10/17 If you heat up a magnet to a high temperature, it can lose its magnetic property and become just a lump of metal. Use what you’ve learned so far to explain why. Objective To learn about the forces created by magnetic fields Tonight’s Homework pp 499: 5, 6, 7 Notes on Magnetism from Current How are magnetism and electricity related? L ‘Oersted found that if he brought an electric wire near a magnet (compass), the magnet would deflect. Notes on Magnetism from Current How are magnetism and electricity related? L ‘Oersted found that if he brought an electric wire near a magnet (compass), the magnet would deflect. It seems that moving electricity – or electric current – induces a magnetic field! Notes on Magnetism from Current A straight wire is the simplest setup we can create. The magnetic field goes around the wire perpendicular to it. Notes on Magnetism from Current A straight wire is the simplest setup we can create. The magnetic field goes around the wire perpendicular to it. The farther we get from the wire, the weaker the field gets. There’s a trick to remembering which way the field goes. Notes on Magnetism from Current This is called the right hand rule. If you point your thumb along the wire, your fingers will curl in the direction of the magnetic field. Notes on Magnetism from Current If electricity can create magnetic field lines, it can turn ferromagnets into magnets as long as a current is running through it. Notes on Magnetism from Current If electricity can create magnetic field lines, it can turn ferromagnets into magnets as long as a current is running through it. We call this an electromagnet. It can be turned on and off at will. We’ll go into more depth on this later! Notes on Magnetism from Current If we shoot a charged particle into a magnetic field it will be deflected. For an electron, we can use the relationship shown here: Notes on Magnetism from Current If we shoot a charged particle into a magnetic field it will be deflected. For an electron, we can use the relationship shown here: “Current” is the direction the electron is moving. “Force” is the direction the electron will be bent. This is usually called the “FBI” rule. Notes on Magnetism from Current For positively charged particles, just use your left hand instead of your right. Notes on Magnetism from Current Imagine we place a wire in a magnetic field. This has a whole stream of charged particles and will be bent as well. Notes on Magnetism from Current Imagine we place a wire in a magnetic field. This has a whole stream of charged particles and will be bent as well. Our FBI rule works to predict this as well. Equations Force on a wire from magnetism E F = BIL V F: Force in Newtons B: Magnetic field strength in Telsa I: Current through the wire in Amps L: Length of the wire in the field in m. S This equation tells up how much force will bend a wire with current if that wire passes through a magnetic field. To find the direction that it will bend, use the FBI rule. Magnetism from Current Review Two magnets are shown below. Which situation best shows how the magnetic field lines will look? SETUP C A D B E Magnetism from Current Review The core of the Earth acts like one giant magnet. So why does a common refrigerator magnet measure a much higher strength of magnetic field in Teslas? < A) Because you’re farther from Earth’s core than a common magnet. B) Because the Earth’s magnetic field is spread over a whole planet. C) The materials in a refrigerator magnet can generate magnetism more efficiently than those in the center of the Earth. D) All of the above E) None of the above Magnetism from Current Review A “dip needle” is like a compass, but moves up and down instead of side to side. At what location would you need to stand on the Earth to get the dip needle pointing straight down? A B C D E Magnetism from Current Review We have a particle in a magnetic field as shown, moving down. Which diagram best shows which way the electron will move next? x x x x x x x x x x x Bx x x x x x x e SETUP x e e x A B it won’t move e e C D e E Exit Question Which of the following would make the best material for an electromagnet? A) wood B) pencil lead C) skin D) iron E) water