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 (17911867) 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 mechanical. 8. In many cases voltage must either be "steppedup" or "steppeddown" depending on the application. These processes rely on transformer equations, which are P_{P} = P_{S} , 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 V_{P}∙I_{P}= V_{S}∙I_{S} . Physically this is accomplished by the number of turns, N, in each coil. Now we have the equation, V_{P}/V_{S}= N_{P}/N_{S} . 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) substitutein the given information and simplify. USEFUL LINKS AND WEBSITES TO VISIT:
 

