Chapter 21
Magnetism
By Boundless
![Thumbnail](../../../../../figures.boundless-cdn.com/14379/raw/regla-mano-derecha-laplace.jpg)
An electric current will produce a magnetic field, which can be visualized as a series of circular field lines around a wire segment.
![Thumbnail](../../../../../figures.boundless-cdn.com/14290/square/figure-23-02-01a.jpeg)
Permanent magnets are objects made from ferromagnetic material that produce a persistent magnetic field.
![Thumbnail](../../../../../figures.boundless-cdn.com/14382/square/220px-magnet0873.jpg)
Magnetic field lines are useful for visually representing the strength and direction of the magnetic field.
![Thumbnail](../../../../../figures.boundless-cdn.com/15557/square/uter-core-convection-rolls.jpeg)
Earth's magnetic field is caused by electric currents in the molten outer core and varies with time.
![Thumbnail](../../../../../figures.boundless-cdn.com/31210/square/figure-23-04-01a.jpeg)
The magnetic force on a charged particle q moving in a magnetic field B with a velocity v (at angle θ to B) is
![Thumbnail](../../../../../figures.boundless-cdn.com/14036/square/figure-23-04-01a.jpeg)
The right hand rule is used to determine the direction of the magnetic force on a positive charge.
Electric and magnetic forces both affect the trajectory of charged particles, but in qualitatively different ways.
![Thumbnail](../../../../../figures.boundless-cdn.com/15069/square/le-20c-2012-11-27-18-49-25.jpg)
If a charged particle's velocity is parallel to the magnetic field, there is no net force and the particle moves in a straight line.
![Thumbnail](../../../../../figures.boundless-cdn.com/14774/square/figure-23-05-01a.jpeg)
Since the magnetic force is always perpendicular to the velocity of a charged particle, the particle will undergo circular motion.
![Thumbnail](../../../../../figures.boundless-cdn.com/14775/square/figure-23-05-02a.jpeg)
Helical motion results when the velocity vector is not perpendicular to the magnetic field vector.
![Thumbnail](../../../../../figures.boundless-cdn.com/15858/raw/t-cavity-magnetron-diagram.jpg)
Cyclotrons, magnetrons, and mass spectrometers represent practical technological applications of electromagnetic fields.
![Thumbnail](../../../../../figures.boundless-cdn.com/16741/square/rement-setup-for-electrons.jpg)
When current runs through a wire exposed to a magnetic field a potential is produced across the conductor that is transverse to the current.
![Thumbnail](../../../../../figures.boundless-cdn.com/16747/square/figure-23-07-02a.jpeg)
When an electrical wire is exposed to a magnet, the current in that wire will experience a force—the result of a magnet field.
![Thumbnail](../../../../../figures.boundless-cdn.com/16621/square/figure-23-08-01a.jpeg)
A current-carrying loop exposed to a magnetic field experiences a torque, which can be used to power a motor.
![Thumbnail](../../../../../figures.boundless-cdn.com/16743/square/ms4.gif)
Current running through a wire will produce a magnetic field that can be calculated using the Biot-Savart Law.
![Thumbnail](../../../../../figures.boundless-cdn.com/16620/square/figure-23-10-01a.jpeg)
Parallel wires carrying current produce significant magnetic fields, which in turn produce significant forces on currents.
![Thumbnail](../../../../../figures.boundless-cdn.com/17397/square/mass-20spectrometer.jpg)
Mass spectrometers use electric or magnetic fields to identify different materials.
![Thumbnail](../../../../../figures.boundless-cdn.com/17161/square/x-fridgemagnetplethora5734.jpeg)
Ferromagnetism is the property of certain materials that enables them to form magnets and be attracted to magnets.
![Thumbnail](../../../../../figures.boundless-cdn.com/17163/square/gnetic-graphite-levitation.jpeg)
Paramagnetism is the attraction of material while in a magnetic field, and diamagnetism is the repulsion of magnetic fields.
![Thumbnail](../../../../../figures.boundless-cdn.com/17074/square/figure-23-02-06a.jpeg)
Solenoids are loops of wire around a metallic core, and can be used to create controlled magnetic fields.