write a lab report

write a lab report
Magnetic Forces on Wires EQUIPMENT INCLUDED: 1 Basic Current Balance 1 Current Balance Accessory 1 Digital B alance 1 Low Voltage AC/DC Power Supply 1 Base and Support Rod 1 Banana Plug Cord Set -Red (5 pack) 1 Banana Plug Cord Set -Black (5 pack) INTRODUCTION Figure 1 Basic Current Balance setup Magnets are mounted on an iron yoke and placed on a digita l balance (resolution of at least 0.01g). One of the conducting paths is suspended between the magnets. The balance measure men t of the mass of the magnets and yoke prior to any current passing through the conductin g path is “zeroed ” out . Current is then passed through the conducting path, producing a force. The change in reading on the balance can be converted to find the magnetic force between the conductor and magnetic field. Conductors of different length are included to measur e the effect of length on magnetic force. Magnetic field can be varied by changing the number of magnets in the yoke. The power source is used to change the current supplied to the conductor. The Current Balance Accessory includes all the components needed to test the effect of angle on magnetic force. THEORY A current carrying wire in a magnetic field experiences a force that is usually referred to as a magnetic force. The magnitude and direction of this force depend on four variables: The magnitude and direction of the current ( I); the strength of the magnetic field ( B); the length of the wire ( L); and the angle between the field and the wire ( ). This magnetic force can be described mathematically by the vector cross product: ⃗⃗ = ⃗⃗ × ⃗⃗ Or in scalar form, = Using the equipment included in the Magnetic Forces on Wires Experiment, all four variables (I, B, L, and ) can be varied while measuring the resulting magnetic force. SET UP Figure 2. Current loop attache d to yoke ins ide the permane nt mag net . To set up the Current Balance: 1. Mount the Main Unit on a lab stand having with a rod 3/8 inch (1.1 cm) in diameter or smaller. 2. Select a Current Loop, and plug it into the ends of the arms of the Main Unit, with the foil extending down. 3. Place the Magnet Assembly on a balance with at least 0.01 gram sensitivity. Position the lab stand so the horizontal portion of the conductive foil on the Current Loop passes through the pole region of the magnets. The Current Loop shouldn’t touch the magnets. 4. Connect the power supply and ammeter as shown a bove. EXPERIMENT 1 – FORCE VS. CURRENT 1. Choose one of the current loops to use throughout the experiment and recor d the length of the current loop above Table 1. 2. Setup the current balance as shown in figure 1 . 3. “Zero ” out the mass of the magnet holder and magnets with no current flowing . 4. Turn on the power supply a nd set the current to 0.5 A. Determine the new “Mass” of the magnet assembly. Record this value under “Mass” in Table 1 below. 5. Increase the current in 0.5 A increments to a maximum of 5.0 A, each time measuring the new “mass” of the magnet assembly and rec ording this value in Table 1 below. 6. Convert the “new ma ss” to the s ize of the force i n newton then plot a graph of force vs. current. Examine the questions below and addres s these in the discussion section of yo ur lab report . ANALYSIS Current Loop Used: TABLE 1 Current “Mass” For ce (A) (grams) (N ) QUEST IONS 1. What relationship exists between the magnetic force and current through the conductor? 2. What is the physical meaning of the slope of the Force vs. Current graph? 3. What is the physical meaning of the vertical intercept of the Force vs. Current graph? 4. Ca n the vertical intercept be attributed to measurement error? Explain. 5. Write a proportionality expression that represents the relationship between Magnetic Force and Current. EXPERIMENT 2 – FORCE VS. LENGTH OF WIRE 1. Choose the shortest current loop to begin the experiment. 2. Setu p the current balance as shown in figure 1 . 3. “Zero ” out the mass of the magnet holder and magnets with no current flowing . 4. Turn on the power supply and set the current between 2.0 and 3.0 Amps. Record this value above Table 2. 5. Determine the new “Mass” of the magn et assembly. Record this value under “Mass” in Table 2 below. 6. Swing the arm of the main unit up, to raise the present current loop out of the magnetic field gap. 7. Pull the current loop gently from the arms of the base unit. Replace it with the next curr ent loop and carefully lower the arm to reposition the current loop in the magnetic field. 8. Repeat steps 6 -8 for each of the current loops and enter the appropriate data in Table 2. 9. Convert the “new ma ss” to the s ize of the force i n newton then plot a graph of force vs. length . Examine the questions below and addres s these in the discussion section of yo ur lab report . ANALYSIS Current Used: TABLE 2 Length “Mass” For ce (cm) (grams) (N ) QUESTIONS 1. What relationship exists between the magnetic force and length of conductor in the magnetic field? 2. What is the physical meaning of the slope of the Force vs. Length graph? 3. What is the physical meaning of the vertical intercept of the Force vs. Length graph? 4. Can the vertical intercept be attributed to measurement error? Explain. 5. Write a proportionality expression that represents the relationship between Magnetic Force and Length. EXPERIMENT 3 – FORCE VS. MAGNETIC FIELD 1. Insert one magnet into the magnet holder and center the magnet in the holder. 2. Choose one of the current loops to use throughout the experiment and record the length of the current loop above Table 3. 3. Setu p the current balance as shown in figure 1 . 4. “Zero ” out the mass of the magnet holder and magnets with no current flowing . 5. Turn on the power supply and set the current between 2.0 and 3.0 Amps. Record this value above Table 3. 6. Determine the new “Mass” of the magnet assembly. 7. Turn off the power supply to change the current to zero. 8. Swing the arm of the main unit up, to raise the current loop out of the magnetic field gap. 9. Place an additional magnet into the magnet holder aligning the like poles of the magnets. 10. Place the holder on the balance with the North and S outh poles in the same orientation as the last measurement. 11. Lower the arm of the main unit and reposition the current loop inside the magnetic field gap. Be certain the current loop isn’t touching the magnet holder. 12. Ag ain, “zero ” out the mass of the magnet holder and magnets with no current flowing . 13. Turn the power supply on to provide current through the loop. 14. Measure the new “Mass” of the magnet assembly and record this value in Tab le 3. 15. Repeat steps 7 -14 for 3, 4, 5 and 6 magnets. ANALYSIS Current Used: Current Loop Used: TABLE 3 Magnetic Field “Mass” Force (# of magnets) (grams) (N) QUESTIONS 1. What relationship exists between the Magnetic Force and Magnetic Field? 2. What is the physical meaning of the slope of the Force vs. Magnetic Field graph? 3. What is the physic al meaning of the vertical intercept of the Force vs. Magnetic Field graph? 4. Can the vertical intercept be attributed to measurement error? Explain. 5. Write a proportionality expression that represents the relationship between Magnetic Force and Magnetic Fiel d. FINAL ANALYSIS 1. Combine the proportionality expressions for all four experiments into one expression. Force should be on the left side of the expression and the other variables on the right side of the expression. 2. Write a few sentences explaining the relationship between Magnetic Force, Length, Current, Magnetic Field and Angle. 3. How would you convert this expression into an equation? 4. What is the constant of proportionality for this equation? Explain. 5. How could such an equation be used?