Because the area is changing, the magnetic flux through the loop is changing, which
means that an emf will be induced in the loop. To calculate the induced emf, we
first write ɸB = BA = Bℓx, and then, since ∆x/∆t = v (distance/time = speed), we get
We can figure out the direction of the induced current from Lenz’s law. As the rod
slides to the right, the magnetic flux into the page increases. How do we oppose an
increasing into-the-page flux? By producing out-of-the-page flux. For the induced
current to generate a magnetic field that points out of the plane of the page, the
current must be directed counterclockwise (according to the right-hand rule).