1. Topic: Electromagnetic induction Objectives: 1.Calculate the magnetic flux through a coil. 2.Calculate the induced electromotive force (EMF) in the coil by solving problems. 3.Calculate the induced electromotive force (EMF) in a straight conductor by solving problems.

2. Electromagnetic induction is the production of a potential difference (voltage) across a conductor when it is exposed to a varying magnetic field.potential differenceconductormagnetic 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.

3. Magnetic flux is the product of the average magnetic field times the perpendicular area that it penetrates.magnetic field  = ABcos   = magnetic flux in T·m 2 A = area of the coil in m 2 B = magnetic field in T  = angle between B and the area vector(an arrow drawn perpendicular to the plane of the coil)

4.  B  is the angle between B and the area vector (red arrow)

5. Induced EMF in a Coil EMF = - N   t = - N (  f -  i )  t = - N(A f B f cos  f – A i B i cos  i )  t EMF = induced electromotive force in V N = number of turns in the coil A= area of the coil in m 2 B = magnetic field  = magnetic flux in T·m 2  t = time is takes for the flux to change

6. 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

7. xxxxxx B(in) xxxxxx xxxx vx xxxxxx

8. Lenz’s law Remember the negative sign in the equation EMF = - N  ?  t The sign is explained by Lenz’s law.

9. 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.Faraday's Law

11. References http://hyperphysics.phy- astr.gsu.edu/hbase/electric/farlaw.html Van Huevelen, Alan (1986). Physics: a general introduction, 2 nd ed. http://www.youtube.com/watch?v=d_aTC0iKO6 8