down your book in trepidation. If you’re really interested in the integral or differential form of the
equations, you will find them in your physics book (or on a rather popular T-shirt). While we won’t write
the equations, we’ll gladly summarize what they are and what they mean.
• Maxwell equation 1 is simply Gauss’s law: the net electric flux through a closed surface is
proportional to the charge enclosed by that surface.
• Maxwell equation 2 is sometimes called Gauss’s law for magnetism: the net magnetic flux through a
closed surface must always be zero. The consequence of this equation is that magnetic poles come in
north/south pairs—you cannot have an isolated north magnetic pole.
• Maxwell equation 3 is simply Faraday’s law: a changing magnetic flux through a loop of wire induces
an EMF.
• Maxwell equation 4 is partly Ampére’s law, but with an addition called “displacement current” that
allows the equation to be valid in all situations. The principal consequence is that just as a changing
magnetic field can produce an electric field, a changing electric field can likewise produce a magnetic
field.
Practice Problems
Multiple Choice:
1 . A point charge of +1 μC moves with velocity v into a uniform magnetic field B directed to the right,
as shown above. What is the direction of the magnetic force on the charge?
(A) to the right and up the page
(B) directly out of the page
(C) directly into the page
(D) to the right and into the page
(E) to the right and out of the page