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Magnetism and electromagnetism How are magnetic poles and electric charges alike? How do they differ? What subatomic particle’s spin causes magnetism? What is an area of a substance with aligned spins called? What substance is easy to make magnetic? Figure 1 Magnetic poles, like electric charges, can _________ or __________. Magnetic poles are different than electric charges because electric charges can exist _________, a positive charged object or a negative charged object, but magnetic poles always exist in ___________. Objects can be magnetically charged based on the alignment of spinning _____________ in a substance. Areas with the majority of electrons spinning in one direction are called _____________. In a nonmagnetic substance the _________ are random while in a magnetic substance domains are _________. ___________ is a substance whose ____________ can be easily aligned while other substances, like wood, do not have _________ that can be _____________. In which direction are magnetic field lines drawn? Figure 2 What is the needle on a compass? If we picture the earth as a big magnet, which magnetic pole would be in the arctic? Magnetic fields outside of objects are said to go from the _________ pole to the _________ pole. The magnetic field around a bar magnet and a horseshoe magnet are shown below using magnetic field lines. The ________ the magnetic field lines are to one another, the ___________ the magnetic field. The _________ pole of a compass needle (really a little magnet) is attracted toward a _________ pole of another magnet, remember opposites attract. Because the ________ pole of the magnet in a compass is attracted to the top of the earth, the top of the earth acts like the __________ pole of a bar magnet. Magnetic field lines outside a magnet are always drawn from ________ to ________. Figure 3 What can create magnetism in a wire? What is the shape of the magnetic field around a current carrying straight wire? So the _______ pole of the earth is called a _______ pole because the _________ pole of the magnet in a compass is attracted to it, not because the _________ pole of the earth is like the _______ pole of a magnet. Notice that when the earth is drawn as a magnet the magnetic field lines go from _________ pole of the magnet to _________ pole of the magnet just as we saw with the bar and horseshoe magnet. Magnetism is also created when __________ move through a wire. All the __________ are moved the same way so all of the spinning _____________ line up. The magnetic field is _____________ around the wire. How can the magnetic field around a wire be determined? What is the difference between electron flow and current? Left hand rule- (For a straight wire) If you point the _________ on your left hand in the direction of electron flow, your __________ will wrap around the wire in the direction of the magnetic field. The rule changes to a right hand rule if current instead of electron flow is known because current is opposite to electron flow. Figure 4 Left hand rule for electron flow Right hand rule for current In some diagrams of electrical equipment it is necessary to "cut" conductors so that you view them from the ends. In such cases, it is impossible to use arrows to indicate the direction of electric flow. Instead, you use a system of ________ and ____________. How is current or electron flow indicated for “cut” conductors? (Here we’ll just do current) The DOT (figure A below) indicates the current to be flowing ___________ of the conductor (TOWARD you) . The CROSS (figure B below) indicates the current to be flowing __________ the conductor (AWAY from you) . Think of the DOT as the "point" of the arrow coming OUT of the wire, and the cross as the "tail" of the arrow ENTERING the conductor. Figure 5 Draw magnetic field lines around each “cut” wire diagram below A coil of wire with electricity flowing through it will create a magnetic field similar to the field that surrounds a permanent bar magnet How can the left hand rule be used to find the magnetic north pole of a coil of wire with moving electrons? What happens to the rule if current instead of electron flow is known? 2nd left hand rule – (for a coiled wire) If you point your ________ in the direction the electrons are moving around the coil, then your ____________ will point to the magnetic __________ pole. The rule changes to a right hand rule if current instead of electron flow is known because current is opposite to electron flow. Figure 6 How will the two coils in Figure 6 react to each other when electricity flows through them? What is a magnet created with electricity called? How can the strength of an electromagnet be increased? Magnets created using electricity are called __________________. More _________ would create a ____________ electromagnet More ______ in the _____ will create a _______ electromagnet Adding an _____ _______ will create a _____________ electromagnet Figure 7 What will happen to the iron core of an electromagnet after the current is stopped? If the core of an electromagnet is a piece of _______, then it will retain ___________ properties even after the current is stopped. How can magnetism in the iron be destroyed? The magnetism can be destroyed by ___________ the iron or by _____________ it on the ground. Electricity can create magnetism, magnetism can create electricity What is created when a magnet is moved through a coil of wire? When a magnet is passed through the middle of a coil of wire, the magnet pushes or pulls the _____________ in the wire creating a ___________. Figure 8 Here the magnet is being pushed into the coil. The ammeter shows current ____________ in a positive direction. Figure 9 Now the magnet is stationary inside the coil. There is no current produced in the coil, shown by the zero on the ammeter Figure 10 Finally the magnet is being pulled out. The ammeter shows current _____________ in the opposite direction than before. If this were to continue we would end up with ___________ that goes from positive to negative and back again. This is called ___________ current and an AC generator produces this kind of ______________.