Chapter+21

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Chapter 21
=Magnetism Lab=

What is the relationship between magnetic field strength and distance from the source?
1. The objective is stated in the title. What is your hypothesis? As the distance from the source increases, the magnetic field strength decreases and vice versa. There is an inverse cube relationship between the two.
 * Pre-Lab**

2. What is the rationale for your hypothesis?

This is the equation for magnetic field strength. As the equation shows, there is an inverse cube relationship between B (magnetic field strength) and d (distance from the source).

3. How do you think you might test this hypothesis? I will use a device to test the magnetic field strength of a magnet. I will control the distance by putting this device at certain distances away from the magnet. I'll record the magnetic field strength at each distance and put the data into a table. I will then graph the data to determine the relationship between the two variables. The other variables in this equation will remain constant.

4. Read the entire procedure through. Done.

5. Design data table(s) in order to record your observations and calculations.
 * Constant (2*uo*u/4pi) || Distance (m) || Distance Cubed (m^3) || Experimental Magnetic Field Strength (T) || Theoretical Magnetic Field Strength (T) || Percent Error (%) ||

=Making a Motor Activity=

Video of my motor: media type="file" key="Movie on 2011-11-29 at 14.48


 * Discussion Questions:**

1. How does a galvanometer work? A galvanometer is used for detecting and measuring electrical current. When a direct current flow through the coil of the galvanometer, the coil generates a magnetic field. Because this field acts against the magnet inside of the device, the coil twists and pushes against a spring. This spring moves the pointer and the angular deflection is proportional to the amount of electrical current.

2. Define motor and generator. A motor is a devices that turns electrical energy into mechanical energy. A generator is a device that turns mechanical energy into electrical energy.

3. A motor is a device which converts electrical energy into mechanical energy (motion). Explain how your motor does so. The motor first uses the electrical energy from the battery to allow current to flow through the circuit. The current then experiences a force from the magnets of the motor which spins the coil part of the circuit. This movement of the coil is mechanical energy.

4. Why does the one rotor support have only one half of its insulation sanded off? The rotor has one half sanded off because we only want the magnetic force to be facing one direction. The magnetic force hits the part that is sanded off and flips the coil. If the other half was sanded off, the force would hit that part and flip the coil the opposite way, causing the motor to go back and forth, not what we want it to do. We want the coil to rotate so we sand only one half and have the magnetic force hit one side of the coil.

5. 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. Instead of converting chemical energy into mechanical energy, we would now have to do the opposite. The coil would now have to be spun by an outside force, such as a hand. This movement is mechanical energy. With the help of the magnetic field, this would create a current through the wire and into the battery. However, now the battery would have to be replaced by something that stores electrical energy, such as a capacitor. The result would be stored electrical energy inside of an object.

=Lab: Magnetic Force on a Wire=

1. The objective is stated as a question. What is your hypothesis? Include the rationale for your hypothesis. How do you think you might test this hypothesis?
 * Pre-lab Questions**

I believe that there is a direct relationship between magnetic force and magnetic field strength, length of the conductor, current, and angle between the field and the current. My rationale for this is the equation F(magnetic)=BILsin(theta), where B is the magnetic field strength, I is the current, L is the length of the conductor, and theta is the angle. I would test this hypothesis by looking at each variable individually. I would keep B, I, and theta constant, change L, and see the result it has on the magnetic force. I would do this for B, I, and theta as well. These measurements will be calculated using high tech devices such as a magnetic force sensor.

2. Read the entire procedure through.

I read it!

3. Design __data table(s)__ in order to record your observations __and__ calculations.


 * B (Teslas) || I (Amperes) || L (meters) || theta (degrees) || Experimental Magnetic Force (N) || Theoretical Magnetic Force (N) || Percent Error (%) ||

4. Answer the following questions: >> 0.00559=B(.042)(1) >> B = 0.13 T >> y = 0.00197
 * 1) How is the direction of the magnetic force oriented with respect to the directions of magnetic field and current which produced it?
 * 2) The direction of magnetic force is the z component in an x-y plane, if the direction of magnetic field and direction of current were to be x and y. One could use the right hand rule to determine the direction. One's fingers indicate indicate the direction of the magnetic field, while the thumb shows the direction of current. Whichever way the palm is facing is the direction of the magnetic force.
 * 3) How do changes in the angle between the current and the magnetic field affect the force acting between them?
 * 4) The bigger the angle is (max=90 degrees), the bigger the magnetic force will be, assuming the current and magnetic field strength are kept constant.
 * 5) What angle between the current and the magnetic field produces the greatest force?
 * 6) 90 degrees
 * 7) What angle between the current and the magnetic field produces the least force?
 * 8) 0 degrees
 * 9) How is the magnitude of the force of magnetism related to the magnitude of the length of the wire carrying the current?
 * 10) Direct relationship
 * 11) 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.
 * 12) 0.00559=BLsin(90)
 * 1) Find the magnetic force on the conducting loop described above, when the current is 0.352-A.
 * 2) y = 0.00559(.352)

=Chapter 21 Guiding Questions=