Physics for Scientists and Engineers II, Summer Semester Lecture 16: June 29 th 2009 Physics for Scientists and Engineers II

Physics for Scientists and Engineers II, Summer Semester Examples: Chapter 31 Problem m

Physics for Scientists and Engineers II, Summer Semester Examples: Chapter 31 Problem m

Physics for Scientists and Engineers II, Summer Semester Examples: Chapter 31 Problem 48

Physics for Scientists and Engineers II, Summer Semester Examples: Chapter 31 Problem 48 (1) (2) (3) (1) into (3): (4) (4) + 3 *(3): (5) (5) into (3):

Physics for Scientists and Engineers II, Summer Semester Chapter 32: Inductance Imagine you suddenly close the switch (SW) on the right side.

Physics for Scientists and Engineers II, Summer Semester The switch-on process in “slow motion” A current will start to flow in the indicated direction (until it reaches a maximum). Before the switch is closed there was no magnetic field created by the wires of this loop. As the current increases, an increasing magnetic field builds up in the interior of this loop due to the current in the wires.  The magnetic flux through the loop increases.  An emf is induced in the loop according to Faraday’s law. (Think of this as a slow-motion observation of the switch-on process. The current doesn’t go from zero to maximum in no time. It takes a finite amount of time to reach maximum).

Physics for Scientists and Engineers II, Summer Semester Polarity of induced emf

Physics for Scientists and Engineers II, Summer Semester Flux calculation

Physics for Scientists and Engineers II, Summer Semester Inductance This parameter combination is purely geometric. Let’s replace it with “L”. L is also called the “Inductance” of a certain conductor configuration (like this particular wire loop). Other geometries result in different inductances.

Physics for Scientists and Engineers II, Summer Semester Kirchhoff’s loop rule

Physics for Scientists and Engineers II, Summer Semester Kirchhoff’s loop rule

Physics for Scientists and Engineers II, Summer Semester Measuring the time constant t I(t)

Physics for Scientists and Engineers II, Summer Semester Circuit Diagram + - Symbolically represent the inductance of the whole loop with one circuit element.

Physics for Scientists and Engineers II, Summer Semester Kirchhoff loop rule during switch-on process + -

Physics for Scientists and Engineers II, Summer Semester Kirchhoff loop rule during switch-on process + -

Physics for Scientists and Engineers II, Summer Semester Kirchhoff loop rule during switch-off process + -

Physics for Scientists and Engineers II, Summer Semester Measuring the time constant from switch-off process t I(t)

Physics for Scientists and Engineers II, Summer Semester Making sense of the time constant

Physics for Scientists and Engineers II, Summer Semester Back to flux and inductance calculations