Magnetism, Magnetic Fields, and Electromagnetism
Magnetism and Magnetic Fields
Centuries before Christ, it was known that some iron ores, like magnetite, attracted small pieces of iron. This property is called magnetism. Objects possessing this property can be natural magnets, such as magnetite or the Earth itself, or artificial magnets made of magnetized iron or other ferromagnetic metals like manganese and cobalt.
Magnetic Field
A magnetic field is the disturbance caused by a magnet in an area of space. It manifests through interactions with other magnets or moving electrical currents (charges) within that area. Graphically, the magnetic field is represented by lines of force that are always closed loops, tangent at all points to the field strength.
Solenoids and Electromagnets
A solenoid is a set of coils, usually circular, arranged parallel to each other with a very small radius compared to their length. When an iron core is introduced inside the solenoid, the device is called an electromagnet or coil.
Circulation of the Magnetic Field
The circulation of the magnetic field along a closed line is the product of magnetic permeability and the intensity of the current passing through the surface bounded by that line. In conservative fields, the circulation along a closed line is zero. However, this is not the case for magnetic fields, meaning they are not conservative.
Motion of a Charge in a Magnetic Field
The magnetic force, being perpendicular to the velocity of a moving charge, changes the direction of the velocity but not its magnitude. This causes the charge to experience only normal acceleration. Therefore, when a moving charge enters a magnetic field, its path curves. In a uniform (constant intensity) magnetic field, the motion of the charge is circular and uniform.
Analogy and Differences Between Electric and Magnetic Fields
Analogy:
- Both electric and magnetic fields are created by electric charges.
- The intensity of both fields is inversely proportional to the square of the distance from the source.
- Both fields are affected by the material medium.
Difference:
- Magnetic fields are generated by moving charges, while electric fields are generated by stationary charges.
- Electric field lines are open, while magnetic field lines are closed loops.
- Electric charges can exist in isolation (positive or negative), but magnetic poles always come in pairs (north and south).
- Electric fields are conservative (central force fields), while magnetic fields are non-conservative.
- Potential energy is defined for electric fields but not for magnetic fields.