Page 350 - Schaum's Outline of Theory and Problems of Applied Physics

CHAPTER 28

Electromagnetic

Induction

ELECTROMAGNETIC INDUCTION

A current is produced in a conductor whenever it cuts across magnetic field lines, a phenomenon known as
electromagnetic induction. If the motion is parallel to the field lines of force, there is no effect. Electromagnetic
induction originates in the force a magnetic field exerts on a moving charge: When a wire moves across a magnetic
field, the electrons it contains experience sideways forces which push them along the wire to cause a current
(see Fig. 27-5). It is not even necessary for there to be relative motion of a wire and a source of magnetic field,
since a magnetic field whose strength is changing has moving field lines associated with it and a current will be
induced in a conductor that is in the path of these moving field lines.
When a straight conductor of length l is moving across a magnetic field B with the velocity v, the emf
induced in the conductor is given by
Induced emf = V = Blv
when B, v, and the conductor are all perpendicular to one another. Figure 28-1 shows the right-hand rule for the
direction of an induced current.

S N
v

Induced B
current I

Fig. 28-1. (From Modern Technical Physics, 6th Ed., Arthur Beiser, c 1992. Reprinted by permission of Pearson
Education, Inc.)

FARADAY’S LAW
Figure 28-2 shows a coil (called a solenoid)of N turns that encloses an area A. The axis of the coil is parallel
to a magnetic field B. The quantity BA is called the magnetic flux enclosed by the coil and is denoted by the
335