Magnetic Fields

1. Visualize Magnetic Field Lines

1. Obtain a segment of straight conducting wire (at least several cm long), and a DC current source.
2. Obtain a plate with a hole in the middle and several small compass needles on the plate, each mounted on a pin and freely rotatable.
3. Feed the conducting wire through the hole so the straight section is perpendicular to the plate. Connect the conducting wire to the DC current source, as shown in Figure 2a. The connection can be made by cables with clamps.
4. Turn on the current source and supply +5 A of current in the wire. Observe the behavior of the compass needles.
5. Reverse the current to −5 A and observe the behavior of the compass needle again.
6. Disconnect and remove the conducting wire and the current source. Obtain and bring a permanent bar magnet with its long-axis parallel to the board, to approach the plate from the side, with the north end of the magnet closer to the plate, as shown in Figure 2b. Observe the behavior of the compass needles.
7. Flip the orientation of the bar magnet, with now its south end closer to the plate. Observe the behavior of the compass needles.

Figure 2: Diagram showing experimental setups using (a) a current flowing in a straight segment of wire that runs perpendicular to a plate and through the center hole on the plate; or (b) a bar magnet brought close to the plate and oriented perpendicular to the plate, to generate magnetic fields, which will orient compass needles on the plate along the direction of the local magnetic fields.

2. Effect of Magnetic Field

1. Obtain two long and parallel conducting wires anchored on a framework, as shown in Figure 3a. If needed, one can use a wood frame with two parallel bars (top and bottom) and anchor or tape the two ends of the wires to the two bars.
2. Use cables and clamps to connect the two wires in series and to the power source, with the top end of one wire connected to the bottom end of the other wire, as shown in Figure 3a.
3. Turn on the power source so that current will flow in the same direction (flowing from top to bottom) in the two wires. Observe the two wires when the current is on.
4. Turn off and disconnect the power source, now reconnect the two wires such that they are now connected again in series to the source, but with the top ends of the two wires shorted, as shown in Figure 3b.
5. Now turn on the power source and observe that the current will flow through the two wires in opposite directions. Observe the two wires.

 

Figure 3: Diagram showing experimental setups of two parallel wires with current flowing in the same (a) or opposite (b) directions.