Magnets attract certain metals. They generate an invisible force field, drawing some materials close while leaving others unaffected. This prompts questions about how different substances interact with these magnetic forces, particularly materials like copper.
The Direct Answer: Copper and Magnets
Copper does not stick to magnets. Pure copper is a non-magnetic material that does not exhibit strong attraction to a magnet. Instead, copper shows a very slight repulsion when exposed to a magnetic field. This behavior classifies copper as a diamagnetic material.
Understanding Different Magnetic Behaviors
Materials interact with magnetic fields in three main ways.
Ferromagnetism describes materials that are strongly attracted to magnets and can become magnetized themselves, such as iron, nickel, and cobalt. In these substances, electrons have unpaired spins that align within regions called magnetic domains, creating a strong overall magnetic moment.
Paramagnetic materials, like aluminum, show a weak attraction to magnetic fields. They contain unpaired electrons whose magnetic moments align weakly and temporarily in an external magnetic field, disappearing once the field is removed.
Diamagnetic materials, which include copper, are weakly repelled by magnetic fields. All electrons in these substances are paired, canceling their individual magnetic moments. When an external magnetic field is applied, it induces a very slight opposing magnetic field within them.
Copper’s Unique Interaction with Magnetic Fields
Copper interacts distinctly with changing magnetic fields through eddy currents. When a magnet moves near a copper surface, or a copper object moves through a magnetic field, the changing magnetic flux induces circular electric currents within the copper, known as eddy currents. According to Lenz’s Law, these eddy currents generate their own magnetic field that opposes the change in the original magnetic field that caused them. This opposition creates a temporary repulsive or dragging force. For instance, if a strong magnet is dropped through a copper tube, the eddy currents induced in the copper create a magnetic field that slows the magnet’s descent. This demonstrates how copper’s electrical conductivity allows for dynamic interactions with magnetic fields.
Everyday Examples of Magnetic Interactions
Magnetic principles are applied in many technologies, with ferromagnetic materials used in refrigerator magnets, compasses, and electric motors. Beyond simple attraction, copper’s unique interaction with magnetic fields is leveraged in practical applications. For example, magnetic braking systems in trains use copper plates where eddy currents are induced by moving magnets, creating a smooth, non-contact braking force. Induction cooktops also use this principle: while pure copper pans do not work directly as they are not ferromagnetic, the changing magnetic field induces eddy currents in the magnetic base of compatible cookware, generating heat. Additionally, copper’s high electrical conductivity and non-magnetic nature make it suitable for wiring in electromagnets and electrical components, minimizing unwanted magnetic interference.