equals the product of the magnetic field strength, the surface area of a loop, and the
number of loops in the coil.
The current flowing through the coil on the left creates a magnetic field. As that current
changes over time, so does the magnetic field it generates, which means the magnetic
flux passing through the coil on the right changes. That change in magnetic flux induces
an emf in the coil on the right, which in turn causes the current in the circuit on the right.
This process is used to illustrate a general principle, called Faraday’s law: A change in
magnetic flux induces an emf. In Equation 1, you see this expressed in mathematical
form. Faraday’s law states that the induced emf equals the negative of the rate of
change of magnetic flux.
Faraday’s law is often applied to a coil having N loops, as we do in this section, and we
state this version in Equation 2. In this case, the flux refers to the flux passing through
each loop, and the total flux equals the flux passing through each loop times the
number of loops.
The negative sign appearing in both equations indicates that the induced emf acts to
“oppose” the change in magnetic flux that causes it. What this means is explained in
more depth in a later section.Faraday’s law, total flux
Ǜ = induced emf
ĭB = total magnetic flux through
circuit
t = time
Faraday’s law, coil of N loops
ĭB = magnetic flux through one loop
N = number of loops
The field passes through six
loops. What is the induced emf?
A = ʌr^2 = ʌ(0.53 m)^2 = 0.88 m^2
(^544) Copyright 2007 Kinetic Books Co. Chapter 29