An electromagnet is a large inductor, and resists changes in the current through its windings. Any sudden changes in the winding current cause large voltage spikes across the windings. This is because when the magnet is turned on, energy from the circuit must be stored in the magnetic field, and when it is turned off the energy in the field is returned to the circuit.When a magnetic field higher than the ferromagnetic limit of 1.6 T is needed, superconducting electromagnets can be used. Instead of using ferromagnetic materials, these use superconducting windings cooled with liquid helium, which conduct current without electrical resistance. These allow enormous currents to flow, which generate intense magnetic fields.
Two parallel conductors, carrying currents, attract if the currents
are parallel, and repel if the currents are antiparallel. The force is a magnetic force. Basically, one wire
produces a magnetic field, which, in turn, exerts a force on the other wire.
Magnetic flux: If a uniform magnetic field B exists in space, then
the magnetic flux through a surface, of area A, placed perpendicular to the field, is BA. If the normal to the
plane surface makes an angle theta with B, then the magnetic flux through the surface is BAcos(theta). For a
general case when either B is not uniform, and/or the surface is not flat, the flux is the integral of B.da over
Gausss law in magnetism: The magnetic flux through any closed
surface is zero.
Magnetic Field Produced By Current, Part 3
Lecture Slides are screen-captured images of important points in the lecture. Students can download and print out these lecture slide images to do practice problems as well as take notes while watching the lecture.