Magnetic circuit and electromagnetism are concepts related to the behavior of magnetic fields in materials and circuits. Retentivity is a property of magnetic materials that characterizes their ability to retain magnetization after an external magnetic field is removed.
Magnetic Circuit:
A magnetic circuit is analogous to an electric circuit but deals with the flow of magnetic flux instead of electric current. It consists of various elements like magnetic materials (ferromagnetic, paramagnetic, and diamagnetic), air gaps, and other structures that guide and manipulate magnetic fields. Just as an electric circuit has resistance, inductance, and capacitance, a magnetic circuit has properties like reluctance, permeability, and magneto-motive force (MMF).
Reluctance: This is the magnetic equivalent of resistance in an electric circuit. It measures how much opposition a magnetic circuit offers to the flow of magnetic flux. Reluctance depends on the geometry and material properties of the circuit.
Permeability: Permeability is a property of materials that describes how easily they allow magnetic lines of flux to pass through them. Different materials have different permeabilities, and in ferromagnetic materials, the permeability can greatly increase due to the alignment of magnetic domains.
Magneto-motive Force (MMF): MMF is the force that drives the magnetic flux through a magnetic circuit. It's analogous to electromotive force (EMF) in an electric circuit and is measured in ampere-turns.
Electromagnetism:
Electromagnetism is a branch of physics that deals with the study of electric and magnetic fields and their interactions. It encompasses the behavior of charged particles, the creation of magnetic fields by electric currents, and the induction of electric currents by changing magnetic fields.
Ampère's Law: This law relates the circulating magnetic field around a current-carrying conductor. It states that the magnetic field around a closed loop is directly proportional to the current passing through the loop.
Faraday's Law of Electromagnetic Induction: This law states that a change in magnetic field through a loop of wire induces an electromotive force (EMF) and subsequently an electric current in the loop. This is the basis for generating electricity in generators and the function of transformers.
Lenz's Law: Lenz's law is a consequence of Faraday's law and states that the direction of the induced EMF and current will always oppose the change in magnetic flux that produced it.
Retentivity:
Retentivity, also known as residual magnetism or remanence, is a property of magnetic materials that measures their ability to retain a certain level of magnetization even after the external magnetic field is removed. Materials with high retentivity can "remember" and maintain a strong magnetic state, while materials with low retentivity lose their magnetization quickly.
Ferromagnetic materials, such as iron and steel, have high retentivity due to the alignment of their magnetic domains. They can be easily magnetized and retain their magnetism even when the external magnetic field is removed. This property makes them useful for creating permanent magnets and for applications in transformers, electric motors, and other magnetic devices.
In summary, understanding magnetic circuits and electromagnetism involves grasping concepts like reluctance, permeability, MMF, Ampère's law, Faraday's law, and Lenz's law. Retentivity is a key property of magnetic materials, determining their ability to retain magnetization after the removal of an external magnetic field.