Current as a source of magnetic fields investigation

Lab D9: Current as a Source of Magnetic Fields Investigation equipment long wire ammeter DC power source capable of delivering several amps per group: 1 compass 1 nail or bolt 1 clear plastic cup paperclips ruler

Extend a very long piece of wire (zip cord is about the right gauge) in a large loop around the room.

Attach a DC current source to either end of the wire loop, paying attention to which terminal is positive.

I. STRAIGHT CURRENT-CARRYING WIRE / EARTH[Otilde]S FIELD

A) With the current off, orient a portion (about 20cm) of the wire horizontally north/south. Hold a compass just under the wire and note how the needle is pointing. Turn on the power source and observe the behavior of the compass needle. Move the compass above and then beside the wire while observing the compass. Notice how distance from the wire affects the compass needle. Sketch the shape, direction, and density of the magnetic field lines in the vicinity of the straight current-carrying wire, making sure you denote the current direction in the wire. Turn off the current and observe the compass needle behavior. Summarize your findings. Why didn[Otilde]t we orient the wire east/west?

B) With the current off, orient a portion (about 20cm) of the wire vertically. Hold a compass right beside the wire and note how the needle is pointing. Turn on the power source and observe the behavior of the compass needle. Move the compass around the wire while observing the compass. Notice how distance from the wire affects the compass needle. Sketch the shape, direction, and density of the magnetic field lines in the vicinity of the straight current-carrying wire, making sure you denote the current direction in the wire. Turn off the current and observe the compass needle behavior. Summarize your findings.

C) Again use the vertically oriented wire with the current on. Hold your compass north of the wire and record the distance from the wire when the compass needle points at an angle of 45 degrees with the north/south direction. Repeat the measurements directly south of the wire. Finally, use an ammeter (that can handle several amps) to measure the current flowing in the wire. Use your measurements to determine the horizontal component of the earth[Otilde]s magnetic field at this location. Compare to the ÒknownÓ value--be sure to cite your source properly. Completely explain your reasoning and all calculations.

II. CURRENT LOOP

With the current off, make a single loop of wire (about 5cm diameter) and hold it such that the plane of the loop is oriented north/south. Hold your compass in the middle of the loop, noticing the needle orientation. Turn on the current and observe the compass needle. Observe the needle behavior as you move the compass around the wire and into and out of the loop. Sketch the shape, direction, and density of the magnetic field lines in the vicinity of the single loop of current, making sure you denote the current direction in the wire. Turn off the current and observe the compass needle behavior. Summarize your findings. Is the shape, direction, and density of these field lines consistent with your findings for a straight current-carrying wire? Explain. Are there any magnetic poles? Explain.

III. CURRENT-CARRYING COIL

A) With the current off, make several loops around a clear plastic cylinder or cup. Do not overlap the loops. Hold the coil so that its long axis is oriented horizontally east/west. Hold your compass in the middle of the coil, noticing the needle orientation. Turn on the current and observe the compass needle. Observe the needle behavior as you move the compass around and into and out of the coil. Sketch the shape, direction, and density of the magnetic field lines inside and near the current-carrying coil, making sure you denote the current direction in the wire. Turn off the current and observe the compass needle behavior. Summarize your findings. Is the shape, direction, and density of these field lines consistent with your findings for a single loop of current? Explain. Are there any magnetic poles? Explain.

B) With the current off, make several tightly packed loops around a nail or bolt. Do not overlap the loops and make them loose enough to slide the nail out. Slide out the nail. Hold the coil so that its long axis is oriented horizontally east/west. Hold your compass near one end of the coil, noticing the needle orientation. Turn on the current and observe the compass needle. Observe the needle behavior as you move the compass around and near the ends of the coil. Sketch the shape, direction, and density of the magnetic field lines near the current-carrying coil, making sure you denote the current direction in the wire. Turn off the current and observe the compass needle behavior. Summarize your findings. Have you seen this field shape before in a no-current situation? Are their any obvious magnetic poles? Explain. Try picking up some paperclips or a key ring with the current-carrying loop. Record your results. Try picking up some paperclips or a key ring with the current turned off. Record your results. Also try picking up some paperclips or a key ring with the nail alone to see if it is magnetized. Record your results.

IV. ELECTROMAGNET

With the current off, replace the nail in the coil. Turn on the current and try picking up the paperclips, keyrings, etc. with the wrapped nail. Record your results, comparing to your previous observations. Try picking up some paperclips or a key ring with the current turned off. Record your results. Explain what caused these effects--be specific.