8.02Experiment 5: Magnetic Fields of a Bar Magnet and Helmholtz CoilINTRODUCTION3. Magnetic Field SensorGENERALIZED PROCEDUREThis lab consists of three main parts. In each you will measure the magnetic field generated either by bar magnets or by current carrying coils.Part 2: Constructing a Magnetic Field DiagramA pair of bar magnets are placed so that either their opposite poles or same poles are facing each other and you will map out the field lines from these configurations.In this part you will use the magnetic field sensor to measure the amplitude of the magnetic field generated from three different geometries of current carrying wire loops.END OF PRE-LAB READINGIN-LAB ACTIVITIESEXPERIMENTAL SETUPNOTE: When working with bar magnets, please do NOT force a north pole to touch a north pole (or force south poles to touch), as this will demagnetize the magnets.MEASUREMENTSPart 1: Mapping Magnetic Field Lines Using Mini-CompassesPart 2: Constructing a Magnetic Field Diagram2A: Parallel Magnets2B: Anti-Parallel MagnetsPart 3: Helmholtz Coil3A: Using a Single Coil3B: Helmholtz Configuration3C: Anti-Helmholtz ConfigurationMASSACHUSETTS INSTITUTE OF TECHNOLOGYDepartment of Physics8.02Experiment 5: Magnetic Fields of a Bar Magnet and Helmholtz CoilOBJECTIVES 1. To learn how to visualize magnetic field lines using compasses and a gauss meter2. To examine the field lines from bar magnets and see how they add3. To examine the field lines from a Helmholtz coil and understand the differencebetween using it in Helmholtz and anti-Helmholtz configurations.PRE-LAB READINGINTRODUCTIONIn this lab we will measure magnetic field lines using two methods. First, we will usesmall compasses that show the direction, but not magnitude, of the local magnetic field.Next we will use a gauss meter, which measures the magnitude of the magnetic fieldalong a single, specific axis and thus does not allow as easy a visualization of themagnetic field direction. We will measure fields both from bar magnets and from aHelmholtz coil.APPARATUS1. Mini-CompassYou will receive a bag of mini-compasses (Fig. 1a) that indicate the magnetic fielddirection by aligning with it, with the painted end of the compass needle pointing awayfrom magnetic north (i.e. pointing in the direction of the magnetic field). Conveniently,the magnetic south pole of the Earth is very close to its geographic north pole, socompasses tend to point North (Fig. 1b). Note that these compasses are cheap (thoughnot necessarily inexpensive) and sometimes either point in the direction opposite the waythey should, or get completely stuck. Check them out before using them.E03-1(a) (b)Figure 1 (a) A mini-compass like the ones we will be using in this lab. (b) The paintedend of the compass points north because it points towards magnetic south.E03-22. Logger Pro InterfaceAs always, we will use the Logger Pro interface, this time for recording the magneticfield magnitude as measured by the magnetic field sensor (gauss meter).3. Magnetic Field SensorThe magnetic field sensor measures the strength of the magnetic field pointing into themeasurement end. The device can be set to measure two different directions, radial andaxial, by pivoting its head. It also has two ranges of operation, 0.3 mT and 6.4 mT.QuickTime™ and a decompressorare needed to see this picture.Figure 2 Magnetic field sensor. Two modes of operation include radial and axial. Tworanges include 0.3 mT and 6.4 mT.4. Helmholtz CoilConsider the Helmholtz Coil Apparatus shown in Fig. 3. It consists of two coaxial coilsseparated by a distance equal to their common radii. The coil can be operated in 3modes. In the first, connections are made only to one set of banana plugs, pushingcurrent through only one of the coils. In the second, a connection is made between theblack plug from one coil to the red plug from the other. This sends current the samedirection through both coils and is called “Helmholtz Mode.” In the final configuration“Anti-Helmholtz Mode” a connection is made between the two black plugs, sendingcurrent in the opposite direction through the two coils.Figure 3 Helmholtz Coil ApparatusE03-34. Power SupplyBecause the Helmholtz coils require a fairly large current in order to create a measurablefield, we are unable to use the output of the Lab Pro device to drive them. For thisreason, we will use an EZ dc power supply (Fig. 4). This supply limits both the voltageand the current, putting out the largest voltage possible consistent with both settings.That is, if the output is open (no leads connected, so no current) then the voltage output iscompletely determined by the voltage setting. On the other hand, if the output is shorted(a wire is placed between the two output plugs) then the voltage is completely determinedby the current setting (V = IRshort).Figure 4 Power Supply for Helmholtz CoilThe power supply allows independent controlof current (left knob) and voltage (right knob)with whichever limits the output the most incontrol. The green light next to the “CV” inthis picture means that we are in “constantvoltage” mode – the voltage setting is limitingthe output (which makes sense since theoutput at the bottom right is not hooked up sothere is currently no current flow).GENERALIZED PROCEDUREThis lab consists of three main parts. In each you will measure the magnetic fieldgenerated either by bar magnets or by current carrying coils.Part 1: Mapping Magnetic Field Lines Using Mini-CompassesUsing a compass you will follow a series of field lines originating near the north pole of abar magnet.Part 2: Constructing a Magnetic Field DiagramA pair of bar magnets are placed so that either their opposite poles or same poles arefacing each other and you will map out the field lines from these configurations.Part 3: Helmholtz CoilIn this part you will use the magnetic field sensor to measure the amplitude of themagnetic field generated from three different geometries of current carrying wire loops.END OF PRE-LAB READINGE03-4IN-LAB ACTIVITIESEXPERIMENTAL SETUP1. Open the Logger Lite file 802_Exp_05_2010.gmbl.2. Connect the Magnetic Field Sensor to channel 1 on the Lab Pro Interface3. Without leads connected to the power supply, turn it on and set the voltage output to 2V. Turn it off.NOTE: When working with bar
View Full Document
Unlocking...