Physics for the Inquiring Mind (PHYS 105) Fall 2005
Activities for Thursday, September 15.
Today we have three stations at which you will work. Consequently, we will be working in the following “Supergroups”: SG1: Amber and Azure; SG2: Crimson and Coral; SG3: Emerald.
SG1 will start at Station 1, SG2 at Station 2, and SG3 at Station 3. The activities at each station are as listed below.
Station 1: The Magnetic Field of a Line Current
The point here is to figure out what the magnetic field produced by a current-carrying wire looks like. There are actually four wires used in this set-up, but that is only to intensify the effect. The result is the same with four wires as it is with one.
Instead of using the magnaprobe to map out the magnetic field as we have been doing thus far, we will use a large ensemble of compasses. Each will point in the direction that the magnetic field points locally, so we will be able to see the field lines simply by following the compass arrows around.
[1] Before you turn the power supply on, make sure that the Voltage knob is turned all of the way clockwise, while the Current knob is turned all of the way counterclockwise. After you have checked this, turn the power supply on.
[2] Turn the Current knob all of the way clockwise and observe what happens to the compass needles. After they have settled down, make a sketch of what the magnetic field around the wires looks like. Remember to put arrows on your field lines that point in the direction that the north pole of each compass points. Make your sketch quickly so that the wires do not overheat.
[3] After you have completed your sketch, turn the current off by rotating the Current knob all of the way counterclockwise again. Reverse the direction of the current flow by swapping the + and - wires on the voltage supply. Then turn the current on again, and sketch the new configuration of magnetic field lines.
[4] Electric current is defined to come out of the + side of the power supply and go back into the - side of the power supply. With this in mind, determine a rule that will allow you to predict which way a compass needle near a current will point when the current is turned on.
Station 2: The Magnetic Field of a Coil
[1] Do part [1] of the Station 1 exercise.
[2] Turn the current on by rotating the Current knob clockwise. Observe how the coil behaves when you bring one of your bar magnets near it.
[3] Determine which side of your coil is a North pole and which side a South pole.
[4] Turn the current off. Is the coil still acting like a permanent magnet? If so, is it as strong as it was with the current on?
[5] Reverse the direction of the current flow by swapping the + and - wires on the power supply. Repeat part [3].
[6] Electric current is defined to come out of the + side of the power supply and go back into the - side of the power supply. With this in mind, determine a rule that will allow you to predict which side of a coil will become a North pole and which side a South pole when a current flows through the coil.
[7] With the current on, insert a paper clip partially into the end of the coil and release it. What happens? Why?
Station 3: Breaking Magnets and the Magnetic Field of Styro-Earth.
[1] Take one of the small ceramic magnets and find its poles. How many poles does it have?
[2] Using the metal end of your screwdriver, shatter the magnet {obviously, protect your eyes when you do this}.
[3] Check the poles of the pieces. Do they all have two poles?
[4] Use your magnaprobe to study the magnetic field of Styro-Earth. Make a sketch depicting the magnetic field lines around Styro-Earth. Mark regions where the magnetic field is pointing into the Earth, and those where the magnetic field is pointing out of the Earth.