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Unformatted text preview: Physics 1BL M AGNETISM Spring 2009 2005 UCSD-PERG Page 1 In this lab, you will focus on the concepts of magnetism and magnetic fields and the interaction between flowing charges (electric current) and magnetic fields. You will find this material in Chapter 19 of Serway and Faughn. It is a good idea to read all of the steps in each part before you start. Pre-Lab Questions 1. For the permanent magnet shown below, draw its magnetic field lines. N S What happens to the North and South poles if you break the magnet in half? Label the appropriate North and South ends for each half. What if you break each piece in half again? And again and again, until you get to what the Greek Atomists called 'the indivisible', or 'the atom'? Can each 'atom' act as a magnet? Use an arrow to represent the magnetic dipole pair S- N . Sketch the atomic dipoles inside of your original, unbroken magnet. 2. The magnetic field a distance 4.0 cm from a long straight current-carrying wire is 4.0 10 5 T. What is the current in the wire? What is the magnetic field at a distance of 15.0 cm from the wire? 3. The diagram shows the cross section of a wire carrying conventional positive current toward us out the plane of the paper. (You may ignore the earths magnetic field) a) By means of an arrow on the diagram, show the direction in which a compass would point if placed at location A and describe the rule you use to remember this effect. b) Show the direction in which the compass would point at two other points of your own choosing. 4. Two wires lie perpendicular to the plane of the paper, and equal electric currents pass through the paper in the directions shown. Point P is equidistant from the two wires. a) Construct a vector diagram showing the direction of the resultant magnetic field at point P. Explain your reasoning. b) If the currents in both wires were instead directed out of the plane of the page (towards us), show the field at point P. Physics 1BL M AGNETISM Spring 2009 2005 UCSD-PERG Page 2 Experiment A: Interactions between Magnets Take two bar magnets, and bring them towards each other slowly. Do they exert a force on each other? Which parts (ends, middle) exert or feel forces from which other parts? Attach the magnets to the wheeled carts so they repel each other. Put the carts close together then release them from rest. What happens? Is the force on cart 1 equal and opposite to the force on cart 2? The carts start with no kinetic energy, but they gain KE when released. Where does the KE come from? Can magnets interact without touching? How does one magnet know the other one is there? Experiment B: Interactions between magnets and compasses NOTE: Do not allow the compass to get close to a strong magnet as this will magnetize them and destroy their accuracy!!...
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