Magnetic fields surround magnetic materials and electric currents and are detected by the force they exert on other magnetic materials and moving electric charges. The magnetic field at any given point is specified by both a direction and a magnitude (or strength); as such it is a vector field. For the physics of magnetic materials, see magnetism and magnet, more specifically ferromagnetism, paramagnetism, and diamagnetism. For constant magnetic fields, such as are generated by magnetic materials and steady currents, see magnetostatics. A changing magnetic field generates an electric field and a changing electric field results in a magnetic field. (See electromagnetism.In view of special relativity, the electric and magnetic fields are two interrelated aspects of a single object, called the electromagnetic field. A pure electric field in one reference frame is observed as a combination of both an electric field and a magnetic field in a moving reference frame.
A compass needle may be used to map the magnetic field lines.
An electric field exerts a force on a charge, whether the charge is
stationary or moving. A magnetic field, however, exerts a force on a charge only if it is moving. The force is
given by F = q v x B; it is the charge q times the cross product of the velocity v and magnetic field
Since the magnetic force is always perpendicular to the velocity, a
magnetic does no work on a moving charge, and thus it does not change its speed.
If a charge, in a region where a uniform magnetic field exists, is
given an initial velocity perpendicular to the field, then it will move in a circle.
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.