Magnetic Fields Lab Report PDF

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My detailed lab reports from Physics 2 Lab with Dr. Sorci....

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Expe r i me n t6 :Ma gne t i cFi e l ds Ma r c h17 , 2 016

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I. PURPOSE The purpose of the experiment is to measure the magnetic field strength at difference distances from the magnet in order to verify the relationship between magnetic field and distance. In addition, the second purpose is to use Ampere’s Law for a solenoid to determine the permeability of free space. II. THEORY Like electric fields, magnetic fields are not visible with the human eye. Their existence is known through their properties and how they interact with their surroundings. Both electricity and magnetism arise from charge; however, the main difference between the two is that electric fields can exists with stationary charges while magnetism is related to charges in motion. Magnetic fields can only exert a force on a moving charge. In physics, a magnetic field is represented by the letter “B”. The standard MKS unit for a magnetic field is Tesla. A Tesla is 1N/amp*m. Magnetic fields can also be measured using the unit of gauss. One gauss is equal to 1 x 10-4 Tesla. There are many different sources of magnetic fields. Magnets exhibit the properties of magnetism. Magnets have two poles, a North pole and a South pole. The magnetic field flows away from the North pole and into the South pole. If a magnet is broken in half, the two resulting halves will each have a North and South pole. A magnetic field sensor can determine the strength of the magnetic field at different distances. The magnetic field gets weaker as it gets further away from the magnet. A solenoid is a coil of wire that is tightly wound into a helical form. Inside the center of the solenoid is a magnetic field that is uniform and parallel to tits axis, except near the end of the solenoid. The magnetic field is only in the center of the solenoid. The magnetic field outside

Callais of the the center of the solenoid is zero. The properties of a solenoid can be described using Ampere’s Law. Ampere’s Law states that for any closed loop path, the length of the solenoid times the magnetic field in the direction of the length is equal to the permeability times the electric current passing through the solenoid.

Figure 1: Diagram of a solenoid. Source: http://physics10aps.blogspot.com/2013/09/solenoid.html

Figure 2: Diagram of a bar magnet. Source: http://www.matsuk12.us/site/Default.aspx?PageID=7508 Standard deviation:

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Percent Error: % Error = |GAV-mean| x 100 GAV Magnetic field (B): B = (µo N / 2r )*I Turn density (n): n = N/L

III. PROCEDURE Set up 1. Open Capstone and chose digit and graph. 2. Connect the Magnetic field sensor to input A on the Pasco 850. 3. On the left hand side in the menu choose hardware setup. 4. On the icon of the Pasco 850 click on the B input and choose magnetic field sensor. 5. For this part the sensor should be set to 1X. 6. On the digit screen choose magnetic field under select measurement.

6.1 Bar Magnet 1. Place bar magnet next to ruler. 2. Hold sensor away from magnet and hit the tare button. 3. Place the sensor 0.5cm from ne end of the bar magnet. Record data. 4. Move sensor 0.5cm away from magnet recording both the distance and B-field strength in table. 5. Dot he same thing for both sides of magnet.

Callais 6.2 Solenoid 1. Plug the high current sensor into Pasco 850. 2. Repeat steps above being sure to add the high current sensor and not simply the current sensor. 3. Set the sensor to 10X. 4. On the graph you can now select measurement on the y-axis to be the magnetic field and on the current on the x-axis. 5. Set up circuit.

6. On the power supply turn the current dial to max and the voltage dial to the voltage dial to zero. Experiment 1. Measure the length of the solenoid and record this along this along with the number turns. 2. Move magnetic field sensor away and tare it. 3. Place the magnetic field sensor in the center of the solenoid using the block. 4. Have instructor check set up. 5. Record and slowly move voltage knob to 17V. 6. Perform a linear fit on graph and record data in table. Repeat 3 times.

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During the course of this experiment, I assisted my lab partners in setting up the the circuit. I recorded measurements and made calculations. V. ANALYSIS

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Magnetic Field vs Distance for South Pole Magnetic Field (gauss)

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-5 -10 -15 -20 -25 -30 -35

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Magnetic Field vs Distance For North Pole Magnetic Field (gauss)

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Distance (cm)

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VI. CONCLUSION This experiment demonstrated the effects of a bar magnet’s magnetic field in relation to the distance away from the object. For the first experiment, the magnetic field of a bar magnet was measured starting from 0.5cm away in increasing implements of 0.5cm to 3.5cm away. This was done for each pole. The magnetic field for the South Pole was initially measured to be -32 gauss at 0.5cm, and the final measurement at 3.5cm was -6 gauss. As the distance away from the magnetic field increased, the strength of magnetic field decreased (but in the negative direction). This is consistent with the expected outcome. As the distance from the magnetic field increases the strength of the magnetic field should decrease. The magnetic field for the North Pole was initially measured to be 33 gauss at 0.5cm, and the final measurement at 3.5cm was 6 gauss. As the distance away from the magnetic field increased, the strength of the magnetic field decreased. This is also consistent with the expected values. The magnetic field is always the strongest the closer it gets to the magnet. Both the curves for the North and South Pole Distance vs. Magnetic Field Strength graphs exhibit an exponential curve with a limit somewhere between 0 gauss and -5 gauss. For the second experiment, a sensor was placed in the center of a solenoid. The solenoid has 3400 turns, and its length was measured to be .0853m. Using the number of turns and the length of the solenoid, the n was calculated to be 39859.3. Three trials were conducted where the voltage was slowly turned up to 17V on the circuit, and the sensor measured the magnetic field inside the solenoid. From the graph, slope, intercept, and goodness of fit was determined. For trial one, the slope was -339, the intercept was 2.76, and the goodness of fit

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was -1. For trial two, the slope was -333, the intercept was 2.57, and the goodness of fit was -1. For trial three, the slope was -343, the intercept was 2.83, and the goodness of fit was -1. Using the slope recorded from the graphs, the permeability of free space was calculated. The calculated permeability of free space was -.0085 gauss*m/amp for trial one, -.0086 gauss*m/amp for trial two, and -.0086gauss*m/amp for trial three. The mean of the calculated permeability of free space was -.0086 gauss*m/amp. Using a graphing calculator, the standard deviation was calculated to be 5.77 x 10-5 gauss*m/amp. The expected value for the permeability of free space constant was 4 x 10-3 gauss*m/amp. The resulting percent error was 31.56%. When referring to the permeability of free space (o), the “o” stands for “of free space.” This experiment can be considered a success, despite a slightly high percent error. The graphs of the magnetic field versus time demonstrated expected results that a magnetic field’s strength decreases as the distance from the magnetic field increases. In addition, through Ampere’s Law, the permeability of free space was relatively accurately calculated. One reason for a slightly high percent error could be due to interference of Earth’s atmosphere and magnetic field. This experiment was not done in a vacuum and therefore was not immune to outside effects. In addition, the error could have been caused by inaccurate measurement tools (i.e. the Capstone program and the sensor)....