H217 Electromagnetic Induction - 1. Notes (1718)

9749 H2 Physics Lecture Notes Topic 17: Electromagnetic Induction Page 1 of 15 Topic 17 Electromagnetic Induction Content  Magnetic Flux  Laws of Electromagnetic Induction Learning Outcomes Candidates should be able to: (a) define magnetic flux and the weber (b) recall and solve problems using Φ = 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

9749 H2 Physics Lecture Notes Topic 17: Electromagnetic Induction Page 2 of 15 17.0 Introduction In the earlier topic, two ways in which electricity and magnetism are related were highlighted: i. an electric current produces a magnetic field, and ii. a magnetic field exerts a force on an electric current or moving electric charge. These discoveries were made in 1820. As nature is often symmetric, the discovery that electric currents produce magnetic fields led scientists to suspect that magnetic fields could produce electric currents. 17.1 Motion Induced Electromotive Force Consider the situation in which a thin straight conductor of length l moving at a constant speed v perpendicular to a uniform magnetic field that is directed into the plane of the page as shown. By Fleming’s Left-Hand Rule, the electrons in the conductor will experience a downward magnetic force FB. This causes the electrons to migrate towards the lower end of the conductor. Thus charge separation occurs within the conductor with the accumulation of negative charge on one end and positive charge on the opposite end. This charge separation will in turn produce an electric field along the rod, which causes the electrons to experience an upward electric force FE. Steady state is reached when there is no further charge separation. This occurs when the magnetic force and electric force acting on the electrons are balanced. i.e. B E induced F F Bqv q l    Hence, the induced e.m.f. across the ends of the conductor is given by induced Blv  x x x x x x x x x x x x x x x x x x x x x x x x v

9749 H2 Physics Lecture Notes Topic 17: Electromagnetic Induction Page 3 of 15 17.2 Magnetic Flux and Magnetic Flux Linkage Ten years after the discovery that an electric current could produce a magnetic field, experiments conducted independently by Joseph Henry in United States and Michael Faraday in England showed that a changing magnetic field could induce an electric current in a circuit. The results of these experiments led to a b asic and important law known as Faraday’s law. But before delving into the Laws of Elec