Question;Name____________________________________________________Section________________Date___________Week 3: Magnetic Fields and Static ElectricityPart 1: Magnetic FieldsBackgroundA magnet moved into the space nears a second magnet, experiences a force as it enters the magnetic fieldof the second magnet. The magnetic field model is a conceptual way of consideringhow two magnets interact with one another. The magnetic field model does not consider the force that one magnet exerts on another one through a distance. Instead, it considers the condition of space around a magnet. The condition of space around a magnet is considered to be changed by the presence of the magnet. Since this region of space, or field, is produced by a magnet, it is called a magnetic field. A magnetic field can be represented by magnetic field lines. By convention, magnetic field lines are drawn to indicate how the north pole of a tiny imaginary magnet would point when in various places in the magnetic field. Arrowheads indicate the direction that the north pole would point, thus defining the direction of the magnetic field. The strength of the magnetic field is greater where the lines are closer together and weaker where they are further apart. Magnetic field lines emerge from a magnet at the north pole and enter the magnet at the south pole. Magnetic field lines always form closed loops.Magnetic field strength is defined in terms of the magnetic force exerted on a test charge of a particular charge and velocity. The magnetic field is thus represented by vectors (symbol B) which define the field strength, also called the magnetic induction. The units are:Since a coulomb(s) is an amp, this can be written aswhich is called a tesla (T). The tesla is a measure of the strength of a magnetic field. Near the surface, the earth?s horizontal magnetic field in some locations is about 2? 10-5 tesla. A small bar magnet produces a magnetic field of about 10-2 tesla, but large, strong magnets can produce magnetic fields of 2 tesla. Superconducting magnets have magnetic fields as high as 30 tesla. Another measure of magnetic field strength is called the gauss (G) (1 tesla = 104 gauss). Thus, the process of demagnetizing something is sometimes referred to as ?degaussing.?In this experiment you will investigate the magnetic field around a permanent magnet.Procedure1. Tape a large sheet of paper on a table, with the long edge parallel to the north-south magnetic direction as determined by a compass.2. Center a bar magnet on the paper with its south pole pointing north. Use a sharp pencil to outline lightly the bar magnet on the paper. Write N and S on the paper to record the north-seeking and south-seeking poles of the bar magnet. Place the bar magnet back on its outline if you moved it to write the N and the S.3. Slide a small magnetic compass across the paper, stopping close to the north-seeking pole of the bar magnet. Make two dots on the paper, one on either side of the compass and aligned with the compass needle. See Figure 3.1.Large sheetNof paperSBar magnetFirst dotNCompassSecond dotFigure 3.14. Slide the compass so the south pole of the needle is now directly over the dot that was at the north pole of the needle. Make a new dot at the north pole end of the compass, exactly in front of the needle. See figure 3.2.5. Continuing the process of moving the compass so the south pole of the needle is over the most recently-drawn dot, then making another new dot at the north pole of the needle. Stop when you reach the bar magnet or the edge of the paper.6. Draw a smooth curve through the dots, using several arrowheads to show the direction of the magnetic flux line.7. Repeat procedure steps 3 through 6, by starting with the compass in a new location somewhere around the bar magnet. Repeat the procedures until enough flux lines are drawn to make a map of the magnetic field.Large sheetNof paperSBar magnetFirst dotNThird dotSecond dot (exactly under south pole of compass).Figure 3.2Results1. In terms of a force, or torque on a magnetic compass needle, what do the lines actually represent? Explain.2. Do the lines ever cross each other at any point? Explain.3. Where do the lines appear to be concentrated the most? What does this mean?Part 2: Static ElectricityBackgroundCharges of static electricity are produced when two dissimilar materials are rubbed together. Often the charges are small or leak away rapidly, especially in humid air, but they can lead to annoying electrical shocks when the air is dry. The charge is produced because electrons are moved by friction and this can result in a material acquiring an excess of electrons and becoming a negatively charged body. The material losing electrons now has a deficiency of electrons and is a positively charged body. All electric static charges result from such gains or losses of electrons. Once charged by friction, objects soon return to the neutral state by the movement of electrons. This happens more quickly in humid air because water vapor assists with the movement of electrons from charged objects. In this experiment you will study the behavior of static electricity, hopefully on a day of low humidity.ProcedurePart A: Attraction and Repulsion1. Rub a glass rod briskly for several minutes with a piece of nylon or silk. Suspend the rod from a thread tied to a wooden meterstick as shown in Figure 3.3. Rub a second glass rod briskly for several minutes with nylon or silk. Bring it near the suspended rod and record your observations in Data Table 3.1. (If nothing is observed to happen, repeat the procedure and rub both rods briskly for twice the time.)2. Repeat the procedure with a hard rubber rod that has been briskly rubbed with wool or fur. Bring a second hard rubber rod that has also been rubbed with wool or fur near the suspended rubber rod. Record your observations as in procedure step 1.1 2 3 4 5 6 7 8 9ThreadMeter stickSuspended rodSecond rodFigure 3.33. Again rub the hard rubber rod briskly with wool or fur and suspend it. This time briskly rub a glass rod with nylon or silk and bring the glass rod near the suspended rubber rod. Record your observations.Part B: Charging by Induction1. Inflate two rubber balloons and tie the ends. Attach threads to each balloon and hang them next to each other from a support. Rub both balloons with fur or wool and allow them to hang freely. Record your observations in Data Table 3.2.2. Bring a glass rod that has been rubbed with nylon or silk near the rubbed balloons. Record your observations.2. Detach one of the balloons by breaking or cutting the thread. Rub the balloon with fur or wool for several minutes. Hold the balloon against a wall and slowly release it. Record your observations.Results1. Describe two different ways that electrical charge can be produced by friction.2. Move a hard rubber rod that has been rubbed with wool or fur near a very thin, steady stream of water from a faucet. Describe, then explain your observations.3. Was the purpose of this lab accomplished? Why or why not? (Your answer to this question should be reasonable and make sense, showing thoughtful analysis and careful, thorough thinking.)Data Table 3.1 Attraction and Repulsion of Glass Rod and Rubber RodInteractionObservationGlass rod-Glass RodRubber rod ? Rubber RodGlass rod ? Rubber rodHow many different kinds of electric charge exist according to your findings above? Explain your reasoning?How do charges interact?Data Table 3.2 Charging by InductionInteractionObservationBalloon ? BalloonRubber rod ? BalloonGlass rod ? BalloonBalloon ? WallWhat evidence did you find to indicate that the balloons had static charges?Explain why a balloon exhibits the behavior that it did on the wall.
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