Ch21_IrwinA

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 * = CHAPTER 21: MAGNETISM =

__ Lab: Magnetic Field Strength __

 * PRELAB QUESTIONS: **
 * 1. The objective is stated in the title. What is your hypothesis? (Attempt to answer the question, to the best of your knowledge.)**
 * The relationship between the electric field strength of a magnet and the distance from the source is an inverse cube relationship.
 * 2. What is the rationale for your hypothesis? (Provide detailed reasoning here. This may take the form of a list of what you already know about the topics, with a summary at the end.**
 * according to the following equation:(where Baxis is electric field strength and d is distance from the source)
 * [[image:Screen_shot_2011-11-21_at_9.41.18_PM.png width="103" height="41"]]
 * 3. How do you think you might test this hypot****hesis? (What might you measure and how?)**
 * Use a magnetic field sensor to find the relationship between the electric field strength of a magnet and the distance from the source. We will control the distance and will measure the magnetic field strength using the sensor.
 * 4. Read the entire procedure through.**
 * 5. Design __data table(s)__ in order to record your observations __and__ calculations. Do this in Excel a post this draft on your wiki.**
 * [[image:Screen_shot_2011-11-21_at_9.56.27_PM.png width="548" height="148"]]

__ Activity: Making a Motor __
__**Video:**__ media type="file" key="Movie on 2011-11-29 at 14.38
 * __Materials:__**
 * Single D-cell battery
 * Two flat ceramic magnets
 * About 1 arms length of wire
 * Sand paper
 * Two paper clips
 * Tape (optional)
 * __Procedure:__**
 * 1) To form the rotor coil, wind approximately 1.5 meters of magnet wire tightly around a test tube, film canister, or some other round object; the diameter of the coil should be between 2.5 to 5 cm. Leave about 7 cm of wire free at each end.
 * 2) Loop the ends of the wire around and through the rotor coil to hold it firmly together so it doesn’t unwind. It is critical that the two end wires are centered and bent parallel to each other across the coil.
 * 3) Completely remove the insulation from one end of the coil wire. To do this, lay the coil flat on the desk and rub the end with sandpaper, turning the wire to scrape off all insulation.
 * 4) At the other end of the coil wire, remove half the insulation.
 * 5) Tape a flat magnet to a D-cell. (To stabilize the D-cell, you may want to tape it to the desk or to an upside-down foam cup.)
 * 6) Bend the paper clips into hooks to support the rotor. Attach them to the D-cell with a rubber band.
 * 7) Place the coil in the paper clip supports. Spin the coil, and it should continue to spin by itself – a working motor! If it does not, proceed to the Troubleshooting Instructions.
 * __Discussion Questions:__**
 * 1) How does a galvanometer work?
 * A galvanometer is an ammeter, used for measuring current. When the current passes through a metal coil in the device, the coil feels the force of the torque created by the magnetic field's force. This force causes rotation at an angle that is proportional to the current.
 * 1) Define motor and generator.
 * A motor is a device that converts electrical energy into mechanical energy.
 * A generator is a device that converts mechanical energy into electrical energy.
 * 1) A motor is a device which converts electrical energy into mechanical energy (motion). Explain how your motor does so.
 * Our motor converts the electrical energy from the battery into the mechanical energy using magnetic force. The mechanical energy (motion) is represented by the spinning coil of wire. It turns because the loop of wire with current has a magnetic field too, which interacts with the magnet's magnetic field.
 * 1) Why does the one rotor support have only ½ of its insulation sanded off?
 * By sanding off the insulation, we are allowing the wire to experience the magnetic force. If we sanded off all of the insulation the wire would be receiving the magnetic force in both directions, making it flip back and forth. By sanding off only half, the magnetic force is only applied to one side, forcing the coil to rotate.
 * 1) How could the motor you built in be converted to a generator? Describe carefully what would have to be changed and what the result would be.
 * We would need some other way to turn the coil other than the current provided by the battery. This could be something like wind turning the coil. Then by connected something like a lightbulb, the mechanical energy from the turning coil would be converted to electrical energy in the light bulb.

__ Lab: Magnetic Force on a Wire __

 * PRELAB QUESTIONS: **
 * Objective: For a conductor placed in a magnetic field, what are the relationships between the magnetic force, magnetic field strength, length of the conductor, current, and angle between the field and the current?**
 * 1) The objective is stated as a question. What is your hypothesis?
 * 2) The relationship between the magnetic force, magnetic filed strength, length of the conductor, current, and angle between the field and the current for a conductor placed in a magnetic field can be represented by the equation F=BIL*sin(theta) where F is magnetic force, B is magnetic field strength, I is current, L is the length of the conductor, and theta is the angle between the field and the current.
 * 3) How do you think you might test this hypothesis? (What might you measure and how?)
 * By changing the length of the conductor we could test the magnetic field strength using a magnetic field strength sensor.
 * 1) Read the entire procedure through.
 * 2) [[image:Screen_shot_2011-12-01_at_9.35.35_AM.png]]
 * 3) Answer the following questions:
 * 4) How is the direction of the magnetic force oriented with respect to the directions of magnetic field and current which produced it?
 * 5) How do changes in the angle between the current and the magnetic field affect the force acting between them?
 * The angle has a direct relationship with the current and the magnetic field strength. So, as the angle increases the current and magnetic field strength will increase until the angle produces the greatest possible force (at 90 degrees).
 * 1) What angle between the current and the magnetic field produces the greatest force?
 * 90 degrees
 * 1) What angle between the current and the magnetic field produces the least force?
 * 0 and 180 degrees
 * 1) How is the magnitude of the force of magnetism related to the magnitude of the length of the wire carrying the current?
 * As the length of the wire increases, so does the magnitude of the force of magnetism.
 * 1) A graph of force vs. current has a trendline with an equation of y = 0.00559x. What is the theoretical magnetic field strength of the magnet used in this experiment if the loop is 4.2-cm long? Show your work.
 * [[image:Screen_shot_2011-12-01_at_9.23.32_AM.png align="center"]]
 * 1) Find the magnetic force on the conducting loop described above, when the current is 0.352-A
 * [[image:Screen_shot_2011-12-01_at_9.23.40_AM.png align="center"]]
 * [[image:Screen_shot_2011-12-01_at_9.23.40_AM.png align="center"]]