WEBSITE NOTES: Electromagnetic Induction.
1. When a conductor of length, L, and velocity, v, moves across a magnetic
field, B, an Electromotive Force (Emf), ε, is induced in the conductor. This is
given by ε = BLv.
2. The current in the conductor is now given by I = ε / R, which is now
Ohm's Law for current from induced Emf.
3. The total magnetic flux through a plane area, A, placed in a uniform
magnetic field depends on the angle between the direction of the magnetic
field and the direction perpendicular to the surface area. The equation is
Φ = BAcos(θ) .
4. Michael Faraday (1791-1867) discovered that when the magnetic flux,
given by the Greek letter Phi, Φ, changes with time, an electromotive force,
or Emf, is produced. Or we can say, ε = -N∙ΔΦ/Δt , with N as the number
of turns in the coil.
5. Since the magnetic flux is the product of the magnetic field, B, the area,
A, and the cos of the angle between the magnetic field and the normal to
the surface, there are three possible ways the flux can change with time;
the field, B, or the area, A, or the angle theta.
6. Lenz's Law: The polarity of the induced Emf is such that it tends to
produce a current that will create a magnetic flux to oppose the change in
flux through the circuit, ε = -ΔΦ/Δt .
7. Remember that a generator changes mechanical energy to electrical
energy. But a motor does the opposite. It changes electrical energy to
8. In many cases voltage must either be "stepped-up" or "stepped-down"
depending on the application. These processes rely on transformer equations,
which are PP = PS , which means that the power of the primary circuit equals
the power generated in the secondary, if ideal.
9. Therefore, since P = VI , we have VP∙IP= VS∙IS . Physically this is
accomplished by the number of turns, N, in each coil. Now we have the
equation, VP/VS= NP/NS .
10. And still, we need these steps to solve any problem in Physics:
(i) read the problem and identify the given variables
(ii) determine what you are asked to solve for
(iii) find the correct equation to use
(iv) use Algebra, Trigonometry, and/or Calculus to isolate the unknown
(v) substitute-in the given information and simplify.
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