Lecture 5 Electromagnetic Field Theory “Our thoughts and feelings have Dr. G. V. Nagesh Kumar Professor and Head, Department of EEE, electromagnetic reality. JNTUA College of Engineering Pulivendula Manifest wisely.” Topics 1. Magnetic circuits, MMF, Reluctance 2. Self and Mutual inductance of simple configurations 2 Magnetomotive Force 3 MMF • Definition: The current flowing in an electric circuit is due to the existence of electromotive force similarly magnetomotive force (MMF) is required to drive the magnetic flux in the magnetic circuit. • The magnetic pressure, which sets up the magnetic flux in a magnetic circuit is called Magnetomotive Force. • The SI unit of MMF is Ampere-turn (AT), and their CGS unit is G (gilbert). • In short, a force which is responsible to drive flux in the magnetic circuit (same as electromotive (EMF) which drives electron in an electric circuit) is known as magnetomotive force . 4 MMF • The strength of the MMF is equivalent to the product of the current around the turns and the number of turns of the coil. • As per work law, the MMF is defined as the work done in moving the unit magnetic pole (1weber) once around the magnetic circuit. • The MMF is also known as the magnetic potential. • It is the property of a material to give rise to the magnetic field. • The magnetomotive force is the product of the magnetic flux and the magnetic reluctance. 5 Reluctance 6 Reluctance • The reluctance (S), of a material is a measure of how difficult it is to produce flux within it. • It represents the opposition to magnetic flux, and depends on the geometry and composition of an object. • Permeability, on the other hand, is a measure of how easily a magnetic field can be set up in a material. • Permeability is the ratio of the flux density of the magnetic field within the material, to its field strength. • To produce a magnetic circuit with low reluctance, the circuit length should be kept short, the material chosen for the magnetic circuit should have a high permeability and the cross sectional area of the circuit should be large. 7 Reluctance 8 Similarities 9 Inductance 10 Inductance of Toroid 11 Inductance of Solenoid 12 Inductance of Coaxial Cable 13 Mutual Inductance 14 Mutual Inductance 15 Mutual Inductance 16 Inductance 17 Magnetic Energy 18 Magnetic Boundary Conditions 19 Boundary Conditions for Normal Component 20 Boundary Conditions for Normal Component 21 MagneticBoundary Conditions Boundary for Conditions Tangential Component 22 MagneticBoundary Conditions Boundary for Conditions Tangential Component 23 MagneticBoundary Conditions Boundary for Conditions Tangential Component 24 Boundary Conditions 25 Problem 26 Problem 27 Problem 28 Problem 29 Problem 30 Problem 31 Problem 32 Problem 33 Problem 34 Problem 35 Problem 36 Problem 37 Problem 38 Problem 39 Problem 40 Problem 41 Problem : GATE 2003 42 Problem : GATE 2003 43 Problem : GATE 2004 44 Problem : GATE 2008 45 Problem : GATE 2016 46 Problem : GATE 2017 47 Problem : GATE 2020 48 Problem : GATE 2020 49 Problem : GATE 1993 Option (a) is Correct 50 Problem : GATE 1994 51 Problem : GATE 1996 Option (b) is Correct 52 Problem : GATE 1996 Option (b) is Correct 53 Problem : GATE 2003 Option (c) is Correct 54 Problem : GATE 2007 55 Problem : GATE 2007 Option (d) is Correct Option (a) is Correct 56 Problem : GATE 2013 Option (c) is Correct 57 Problem : GATE 2015 Option (a) is Correct 58 Thank you Email: [email protected].