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14.2 Magnetic Field Around a Current-Carrying Conductor
 Up until 1820, electricity and magnetism were thought to be
two completely unrelated phenomena.
 Hans Christian Oersted accidentally found that a currentcarrying wire induces a magnetic field. Similarly, a magnetic
field can induce a current in a wire moving through it.
 This “new” are of study became known as
electromagnetism.
A straight current-carrying wire will have a magnetic field around
the wire. The magnetic field lines are circular and decrease in
strength as you move further away from the wire (See p. 525, Fig.
14.17).
Conventions:
Since it is difficult to draw these 3-D configurations on a 2-D page,
certain conventions have been adopted to simplify
communications.
 Current flowing into the page is denoted by an X.
 Current flowing out of the page is denoted by a dot.
 Magnetic field lines are drawn with arrows pointing toward
the “North” of the field.
*Note that magnetic field lines are continuous, but only a few
representative lines one are drawn.
Right-Hand Rule for Straight Conductors:
To determine the direction of the magnetic field lines, point the
thumb of your right hand in the direction of the current flow. Your
fingers will curl in the direction of the magnetic field lines (See
p.536 Fig. 14.18)
Similarly, if you know the direction of the magnetic field, you can
work backwards to determine the direction of the current flow in
the wire.
RHR for a Loop:
Works the same way as for the straight conductor but opposite
ends of the loops have magnetic field lines in opposite directions.
RHR for a Helix:
A helix is a coil of wire. Magnetic fields from all of the individual
wires combine to form a net magnetic field in one direction
INSIDE the helix and in the other direction OUTSIDE the helix
(See p. 527 Fig. 14.21).
To determine the direction of the net magnetic field, the RHR is
slightly modified:
Curl your fingers (on your RIGHT hand) in the direction of the
current flow in the wire and your thumb will point in the direction of
the magnetic field (N).
A helix that contains a core (a ferromagnetic material) is an
electromagnet.
The strength (magnetic force) of an electromagnet depends on:
1. The current in the wire. (Fm  I)
2. The number of turns in the helix. (Fm  N)
3. The permeability of the core (a quantity related to the
ferromagnetic properties of the material). Non-ferromagnetic
materials have a permeability of 1. The higher the
permeability, the stronger the magnetic force.