《Fundamentals of Physics精品教学-华南理工》30 Induction and Inductance.pptVIP

30 Induction and Inductance 30-2 Two Experiments Magnetic force Electric motor 30 Induction and Inductance 30-2 Two Experiments Induction Faraday’s law Hydro power Electric generator 1 Current appears only if there is relative motion; 2 Faster motion produces greater current; 3 Different pole causes different direction of the current. Induced current; Induced emf; Induction 30 Induction and Inductance 30-2 Two Experiments Induced current only appears when the current in the loop is changing and not when it is constant. The induced emf and induced current are caused when something changes. Faraday would tell us 30 Induction and Inductance 30-2 Two Experiments 30-3 Faraday’s Law of Induction Faradays law of induction: An emf is induced in the loop when the number of magnetic field lines that pass through the loop is changing. The explanations of the two experiments 30 Induction and Inductance 30-3 Faraday’s Law of Induction Electric flux: amount of electric field passing through a surface Magnetic flux: the amount of magnetic field through a loop 30 Induction and Inductance 30-3 Faraday’s Law of Induction Volt (V) Ways to change flux: (1) B; (2) A; (3) angle 30 Induction and Inductance emf can appear no matter the circuit is closed or not, but i can not. The long solenoid S has 220 turns/cm and carries a current i=1.5 A. At its center we place a 130-turn coil C of diameter d=2.1 cm. The current in the solenoid is reduced to zero at a steady rate in 25 ms. What is the emf that is induced in coil C? 30 Induction and Inductance Sample Problem 30 Induction and Inductance Sample Problem 30-4 Lenz’s Law An induced current has a direction such that the magnetic field due to the current opposes the change in magnetic flux that induces the current. Opposite to pole movement Opposite to flux change Faraday’s Law + Lenz’s Law 30 Induction and Inductance The magnetic field B=4.0t2+2.0t+3.0 is directed out of the page. An