Introduction to SAT II Physics

The unit of flux is the weber (Wb), where 1 Wb = 1 T · m^2.

Changing Magnetic Flux

As we will see shortly, is more important than : our interest is in how flux changes,
not in its fixed value. The formula for magnetic flux suggests that there are three ways of
changing magnetic flux:

1. Change the magnetic field strength: By sliding a permanent magnet back
   and forth, the magnetic field in a certain area will fluctuate. We will look at this
   phenomenon a bit later in this chapter.


2. Change the area: When a bar slides on rails in a magnetic field, as in our
   discussion of motional emf, the square bounded by the bar and the rails gets
   larger. As it grows, the number of field lines passing through it increases, and
   thus the flux increases as the bar moves.


3. Rotate the area, changing the angle between the area and the
   magnetic field: When the area is perpendicular to the magnetic field, the
   magnetic flux will simply be the product of the magnitudes of the area and the
   magnetic field strength. However, as you rotate the area so that it is at an angle to
   the magnetic field, fewer field lines will pass through it, and so the magnetic flux
   will decrease.

EXAMPLE

A square with sides of length 2 m is perpendicular to a magnetic field of strength 10 T. If

the square is rotated by 60º, what is the change in magnetic flux through the square?

First, let’s calculate the flux through the square before it’s rotated. Because it’s
perpendicular to the magnetic field, the flux is simply the product of the area of the
square and the magnetic field strength: