Topic: Electromagnetic induction Objectives: Define and calculate magnetic flux. Calculate the induced EMF in a coil when there is a changing magnetic flux through it by using Faraday’s law of electromagnetic induction.
Magnetic flux is the product of the average magnetic field times the perpendicular area that it penetrates. = ABcos = magnetic flux in T·m2 A = area of the coil in m2 B = magnetic field in T = angle between B and the area vector(an arrow drawn perpendicular to the plane of the coil)
B is the angle between B and the area vector (red arrow)
Electromagnetic induction is the production of a potential difference (voltage) across a conductor when it is exposed to a varying magnetic field. Discovery was credited to Michael Faraday. Faraday’s law of electromagnetic induction states that any change in the magnetic environment of a coil of wire will cause a voltage (EMF) to be "induced" in the coil.
Induced EMF in a Coil EMF = - N t = - N (f - i) = - N(AfBfcosf – AiBicosi) EMF = induced electromotive force in V N = number of turns in the coil A= area of the coil in m2 B = magnetic field in T = magnetic flux in T·m2 t = time it takes for the flux to change in s
Induced EMF in straight conductor EMF = BLvsin EMF = induced electromotive force in V B = magnetic field in T L = length of the conductor in m v = speed of the conductor in m/s
x x x x x x B(in) x x x x x x x x x x v x
Lenz’s law Remember the negative sign in the equation EMF = - N ? t The sign is explained by Lenz’s law.
Lenz’s law When an emf is generated by a change in magnetic flux according to Faraday's Law, the polarity of the induced emf is such that it produces a current whose magnetic field opposes the change which produces it. The induced magnetic field inside any loop of wire always acts to keep the magnetic flux in the loop constant.
References http://hyperphysics.phy-astr.gsu.edu/hbase/electric/farlaw.html Van Huevelen, Alan (1986). Physics: a general introduction, 2nd ed. http://www.youtube.com/watch?v=d_aTC0iKO68