ASRJC Electromagnetic Induction Notes

ANDERSON SERANGOON JUNIOR COLLEGE PHYSICS 9749 17-1 Additional Notes Topic 17: Electromagnetic Induction Content A Magnetic Flux and Magnetic Flux Linkage B Laws of Electromagnetic induction: Faraday’s Law and Lenz’s Law C Induced e.m.f. in a Straight Conductor D Applications of Electromagnetic induction Learning Outcomes Candidates should be able to: (a) define magnetic flux as the product of an area and the component of the magnetic flux density perpendicular to that area. (b) recall and solve problems using  = BA. (c) define magnetic flux linkage. (d) infer from appropriate experiments on electromagnetic induction: (i) that a changing magnetic flux can induce an e.m.f., (ii) that the direction of the induced e.m.f. opposes the change producing it, (iii) the factors affecting the magnitude of the induced e.m.f. (e) recall and solve problems using Faraday’s law of electromagnetic induction and Lenz’s law. (f) explain simple applications of electromagnetic induction. Demonstrating Science Inquiry Skills In 1819, Hans Christian Oersted discovered that a magnetic compass experiences a force in the vicinity of an electric current. This was the first evidence of a relationship between electricity and magnetism. Because nature is often symmetric, it led scientists to suspect that magnetic fields could in turn produce electricity. Indeed, experiments conducted by Michael Faraday showed that a changing magnetic field could induce an electric current in a circuit. The results of the experiment led to what we know today as Faraday’s law, the application of which led to the production of electrical energy in power generation plants throughout the world.

ANDERSON SERANGOON JUNIOR COLLEGE PHYSICS 9749 17-2 Additional Notes Generation of electric current • Faraday first discovered that current can be induced in a circuit by a changing current in a nearby circuit as shown. Fig. 17.1 Action Observation Switch is closed Galvanometer deflects momentarily. Switch remains closed and current is steady Galvanometer shows no deflection. Switch is open Galvanometer deflects momentarily, but in opposite direction. • Faraday went on to observe that when a bar magnet is moved near a coil, a similar effect is obtained. Fig. 17.2 Action Observation Magnet moves towards/ away from coil Galvanometer deflects momentarily. Coil moves towards/ away from magnet Galvanometer deflects momentarily. Faster relative motion between magnet and coil Larger deflection by galvanometer. • Conclusion: (Induced) electric current is generated by a changing magnetic fiel d linking the coil. A galvanometer is an apparatus which deflects to indicate the presence of a current passing through it. It is able to distinguish between 2 currents in opposite directions. Note that there is no e.m.f. source