Ch21_RabinR

= Chapter 21: Magnetism = // These two websites are excellent resources for notes and sample problems appropriate for AP level: [] and [] // toc

Guiding Questions #1-14
1. Describe magnetic poles and their characteristics. Every natural magnet has both a North pole and South pole, the two strongest ends of the magnet. When two magnets attract, the magnets only attract when the North pole of one magnet is beside the South pole of another magnet, or vice-versa. Source: http://library.thinkquest.org/11924/emagnet.html 2. Describe what is known about the Earth’s magnetic field. The earth is like a big magnet. Although not directly at, the north pole of the magnet is near the top of the planet, near the geographic north pole, and the south pole is near the geographic south pole. Magnetic field lines extend from these poles for tens of thousands of kilometers creating a magnetic field. This magnetic field acts like a force field to protect the planet from things such as space radiation. Source: http://www.universetoday.com/27005/earths-magnetic-field/ 3. What is a magnetic field? A magnetic field is a region around a magnetic material that has an affect of a magnetism force. 4. Why does a compass point north? A compass consists of a small, lightweight magnet balanced on a nearly frictionless pivot point. The magnet is generally called a needle and one end of the needle is often marked "N" and always points towards north. This occurs due to the earth's magnetic field. North poles and south poles of magnets attract each other therefore, the end of the needle that points north is the pole of the needle's magnet that is of opposite charge from earth's magnetic north pole. Source: http://adventure.howstuffworks.com/outdoor-activities/hiking/compass1.htm 5. How is the magnetic force on a charged particle measured? The magnetic force on a charge particle can be measured through the equation Magnetic Force = Charge*Magnetic Field Strength*Velocity*SIN(Theta). 6. What is the magnitude of net force on an electron moving in the magnetic field where //B// = 2 T, //v// = 4 x 104 m/s, and ø= 30o? 7. In the giant CERN particle accelerator in Switzerland, protons are accelerated to speeds of 2.0 x 108 m/s through a magnetic field of 3.5 T and then collided with a fixed target. What is the magnitude of the magnetic force experienced by the protons as they are accelerated around the giant ring? 8. How is the direction of magnetic force on a charged particle determined? The direction of the magnetic force on a charged particle can be determined using the right-hand rule. To use the right-hand rule properly, align your thumb with the direction of the current and align your remaining fingers with the direction of the electric field lines. The direction in which your palm faces will be the direction of the magnetic force. Note: It is possible that there is no way to align your thumb and your fingers with the current and the magnetic field lines. In this case, there is no force. 9. See animation and note your observations: HYPERLINK __ http://webphysics.ph.msstate.edu/javamirror/ipmj/java/partmagn/index.html __Does not work 10. When a charge enters a magnetic field, what is the relative direction of the velocity and the magnetic force? When a charge enters a magnetic field, the velocity and the magnetic field lines form right angels. 11. In what direction will a charge move when it enters a magnetic field? The charge will move in a circular motion. 12. How is the radius of this motion measured? The radius is measured through the equation 13. Go to HYPERLINK "http://physics.nad.ru/Physics/English/el.htm" **__ http://physics.nad.ru/Physics/English/el.htm __** (Look at the animation labeled “Motion of the charged particle in perpendicular magnetic and electrostatic fields.”) See animation and note your observations. Does not work 14. Go to **__ http://www.members.aol.com/judsonewagner/ __** (Click on __ charges within fields __ from E&M. Observe the right-hand animation.) See animation and note your observations. Does not work
 * Units = Newtons
 * Units = Newtons

Pre-Lab: Magnet
1. The objective is stated in the title. What is your hypothesis? The magnetic field strength should be inversely cubed related to the distance of the source. 2. What is the rationale for your hypothesis? This is based on the equation given in the pre-lab assignment and the similarities towards action-at-a-distance forces such as electrostatic force, where distance and force are also inversely related. Since force and magnetic field are directly related, we came to this hypothesis. 3. How do you think you might test this hypothesis? (What might you measure and how?) To test this hypothesis, we may set up a coordinate plane similar to the set up in the equipotential lab, then plotting magnets at different points throughout the setup and then using different devices to find all the variables (current, magnetic field, angle, and length) to solve for the magnetic field strength. 4. Read the entire procedure through. 5. Design __data table(s)__ in order to record your observations __and__ calculations.

Guiding Questions #15-21
15. What is the magnitude of magnetic force on a current-carrying wire? Magnetic force = Magnetic Field Strength*Current*Length*SIN(Theta) 16. What is the direction of magnetic force on a current-carrying wire? Using the right hand rule, the direction is indicated by the direction the thumb points after grasping the current-carrying wire. 17. A 0.90 m long straight wire on board the Voyager spacecraft carries a current of -.10 A perpendicular to Jupiter’s strong magnetic field of 5.0 x 10-4 T. What is the magnitude of the magnetic force experienced by the wire? Magnetic force = Magnetic Field Strength*Current*Length*SIN(Theta) Magnetic Force = 5 x 10-4*.1*.9 Magnetic Force = 4.5 x 10-5 N 18. If a 4.0 m long cord caries a current of 6.0 A, how large a magnetic force is created on the cord by the earth’s magnetic field of 5.3 x 10-5 T when it is perpendicular to the field? When parallel? Magnetic force = 4*6*5.3 x 10-5 Magnetic Force = 1.27 x 10-3 N When parallel magnetic force = 0 19. Describe how and why a current-carrying coil turns in a magnetic field. A current-carrying wire with a magnetic field also has an axle point. Each side of the axle receives different forces based on the direction of the current and the magnetic field. The current-carrying wire now has torque and will experience turns. 20. What is the principle behind the design of motors and generators? A motor is a device that converts electrical energy into mechanical energy while a generator converts mechanical energy into electrical energy. 21. //What is required in order to produce all magnetic fields?// All magnetic fields require current.

Guiding Questions #22-33
22. What is the direction of the magnetic field around a long straight conductor? The magnetic field must be perpendicular to the conductor. 23. How do you figure out the direction of this magnetic field? The right hand rules tells us that as you grasp the the current-carrying wire, the direction in which your thumb points if the direction of the current and the direction in which your four remanding fingers point is the direction of the magnetic field. 24. What happens if a long, straight conductor is wound into a long coil? When the current first passes through the long coil, a magnetic field is created. Although the lines of force are circular near the wire, they become straight and parallel towards the middle of the coil. All of the forces eventually add up creating a direct proportion between strength of the magnetic field and the number of coils. 25. What is Ampere’s Law? What does it mean? Ampere's law produces an equation for the magnetic field strength for a current-carrying wire using the current and area. 26. What is the magnitude of the magnetic field of a long straight current-carrying wire? To find the magnitude of the magnetic field of a long straight current-carrying wire use the equation posted in the previous question. 27. If a single wire has a magnetic field around it, then what happens when there are two parallel wires close to each other? When there are two parallel wires close to each other, each will feel the affects of the others magnetic field. Therefore if their fields go in opposite directions they will repel and if they go in the same direction they will attract. 28. Go to [] and click on induced B-fields in the E&M section. The right hand animation shows parallel wires, while the left shows a single wire. Does not work 29. Describe whether two parallel wires will be attracted or repelled. a) the currents flow in opposite directions. repel b) the currents flow in the same direction in both wires. attract 30. Describe the magnitude and direction of the magnetic field of at the center in a circular conducting loop. The magnitude of the magnetic field can be found using Ampere's Law equation while the direction can be found using the second right hand rule. 31. What is a solenoid? How is it similar to the circular conducting loop? A solenoid is a cylinder wrapped with many loops of conducting current wire. It basically is a circular conducting loop however a solenoid is many circular conducting loops put together. 32. Why does the solenoid have many important applications? The solenoid has many important applications because it can create a field as great as one with other conducting paths such as a bar magnet however a solenoid can be very small and convenient. 33.How is the magnitude and direction of the magnetic field of a solenoid determined? The magnitude of a solenoid can be determined by the equation and the direction can be determined by the right hand rule.

Activity: Make a Motor
media type="file" key="Movie on 2011-11-29 at 15.22.mov" width="300" height="300" Discussion Questions 1. How does a galvanometer work? A galvanometer contains a pointer connected to moving coil often referred to as moving coil galvanometer. When current passes through the coil, the pointer is deflected. 2. Define motor and generator. A motor is a device that converts electrical energy into mechanical energy while a generator converts 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. All motors will have wires carrying current bent into a loop. Based off of the right hand rule, the sides of the loop that are perpendicular to the magnetic field will feel a forces in opposite direction. The opposite forces create torque which will cause the motion. 4. Why does the one rotor support have only ½ of its insulation sanded off? One rotor support only has half of its insulation sanded off to ensure a full rotation. If it were sanded completely, it would receive a force in both directions thus creating a swivel (back and fourth) motion. 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. One way to convert the motor I built into a generator would be replacing the battery source with a light bulb. I would then manually spin the loop to force the bulb to light. Thus converting mechanical energy to electrical energy.
 * Sorry! This was the best I could do!

Pre-Lab: Magnetic Force
1. The objective is stated as a question. What is your hypothesis? (Attempt to answer the question, to the best of your knowledge.) For a conductor placed in a magnetic field, the magnetic force is directly related to the magnetic field strength, the length of the conductor, the current, and the angle between the field and the current. a) Include 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.) Each of the variables tested are those included on the right side of the equation Magnetic Force = Current*Magnetic Field Strength*Length of Conductor*SIN(Theta). In this equation all the variables are multiplied by each other to reach the resulting magnetic force. Therefore, if any of the variables being tested are increased, the magnetic force should increase. Alike, if any of the variable being tested are decreased, the magnetic force should decrease. Thus creating a direct relationship. b) How do you think you might test this hypothesis? (What might you measure and how?) In order to test the hypothesis, it is essential to keep all variables constant while influencing only one variable and observing the influence on the resulting magnetic force. For example, to test the relationship between the current and the magnetic force, using some sort of device, keep the length of the conductor, the strength of the magnetic force, and the angle completely the same and change the current to variations values. Observing the resulting magnetic field should prove our hypothesis correct. 2. Read the entire procedure through. 3. Design __data table(s)__ in order to record your observations __and__ calculations. Do this in Excel (preferable), and post a copy on your wiki. 4. Answer the following questions: a) How is the direction of the magnetic force oriented with respect to the directions of magnetic field and current which produced it? Using the right hand rule one can determine the direction of the magnetic force with respect to the directions of the magnetic field and current. To use the right hand rule properly, align your thumb with the direction of the current and align the remaining fingers with the direction of the magnetic field. The direction in which your palm is facing is the direction of the magnetic force. b) How do changes in the angle between the current and the magnetic field affect the force acting between them? Changes in the angle between the current and the magnetic field have a direct affect on the force acting between them. As the angel increases the force acting between them increase as well. This is due to the equation Magnetic Force = Current*Magnetic Field Strength*Length of Conductor*SIN(Theta). c) What angle between the current and the magnetic field produces the greatest force? 90 degrees d) What angle between the current and the magnetic field produces the least force? 0 and 180 degrees e) How is the magnitude of the force of magnetism related to the magnitude of the length of the wire carrying the current? The magnitude of the force of magnetism has a direct relationship with the magnitude of the length of the wire carrying the current. As the magnitude of the length of the wire carrying the current increases, the magnitude of the force of magnetism increases as well. This is due to the equation Magnetic Force = Current*Magnetic Field Strength*Length of Conductor*SIN(Theta). f) 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. g) Find the magnetic force on the conducting loop described above, when the current is 0.352-A.