Overview

Source: Yong P. Chen, PhD, Department of Physics & Astronomy, College of Science, Purdue University, West Lafayette, IN

Magnetic fields can be generated by moving charges, such as an electrical current. The magnetic field generated by a current can be calculated from the Maxwell equation. In addition, magnetic objects such as bar magnets can also generate magnetic fields due to microscopic dynamics of charges inside the material. Magnetic fields will exert magnetic force on other moving charges or magnetic objects, with the force proportional to the magnetic field. Magnetic fields are fundamental to electromagnetism and underlie many practical applications ranging from compasses to magnetic resonance imaging.

This experiment will demonstrate magnetic fields produced by a permanent bar magnet as well as an electrical current, using small compass needle magnets that align with magnetic fields. This experiment will also demonstrate the force exerted by the magnetic fields produced by a current on another current-carrying wire.

Procedure

1. Visualize Magnetic Field Lines

Obtain a segment of straight conducting wire (at least several cm long), and a DC current source.
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.
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 mad

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Results

For steps 1.3-1.4, before the current is switched on, the compass needles are oriented randomly. After switching on the current, which flows in the wire from top to bottom, the compass needles will align themselves with the local magnetic field in a circular pattern, as depicted in Figure 4a (top view). Upon reversing the current, the magnetic field reverses, as do the orientations of the compasses, as depicted in Figure 4b.

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Application and Summary

In this experiment, we have visualized magnetic fields using compass needles that orient with the local magnetic field. We also demonstrated the Lorentz force of a magnetic field produced by a current on another nearly parallel current.

Magnetic fields play important roles in our everyday life and technology. They are generated by commonly used bar magnets or "kitchen magnets" as well as electromagnets (solenoids), and are used to pick up other magnetic objects. Earth also generates a

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Magnetic Fields