To see how these relations apply, we consider here a classical example of induced emf: that of a sliding bar on two
parallel rails in a magnetic field as shown in Figure 10.3a. The rails are separated a distance d and are shorted together on
one side. The magnetic flux density points out of the page. The bar and the shorted rails form a loop abcd. If we move the bar
to the right at a velocity v, there will be an induced emf in the bar because the loop increases in area and therefore encloses a
larger, changing flux. We wish now to calculate this emf for a bar of length d, flux density B, and velocity v, because this
calculation leads directly to the idea of the DC generator. There are two ways to calculate the emf in this case. One is from
the motional effect; the second is from the change in flux through the loop. The two methods are equivalent, but the
reasoning is quite different. We look at both solution methods and show that they are equivalent: