1. Physics for Scientists and Engineers II, Summer Semester 2009 1 Lecture 16: June 29 th 2009 Physics for Scientists and Engineers II

2. Physics for Scientists and Engineers II, Summer Semester 2009 2 Examples: Chapter 31 Problem 48 0.500m

3. Physics for Scientists and Engineers II, Summer Semester 2009 3 Examples: Chapter 31 Problem 48 0.500m

4. Physics for Scientists and Engineers II, Summer Semester 2009 4 Examples: Chapter 31 Problem 48

5. Physics for Scientists and Engineers II, Summer Semester 2009 5 Examples: Chapter 31 Problem 48 (1) (2) (3) (1) into (3): (4) (4) + 3 *(3): (5) (5) into (3):

6. Physics for Scientists and Engineers II, Summer Semester 2009 6 Chapter 32: Inductance Imagine you suddenly close the switch (SW) on the right side.

7. Physics for Scientists and Engineers II, Summer Semester 2009 7 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).

8. Physics for Scientists and Engineers II, Summer Semester 2009 8 Polarity of induced emf

9. Physics for Scientists and Engineers II, Summer Semester 2009 9 Flux calculation

10. Physics for Scientists and Engineers II, Summer Semester 2009 10 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.

11. Physics for Scientists and Engineers II, Summer Semester 2009 11 Kirchhoff’s loop rule

12. Physics for Scientists and Engineers II, Summer Semester 2009 12 Kirchhoff’s loop rule

13. Physics for Scientists and Engineers II, Summer Semester 2009 13 Measuring the time constant t I(t)

14. Physics for Scientists and Engineers II, Summer Semester 2009 14 Circuit Diagram + - Symbolically represent the inductance of the whole loop with one circuit element.

15. Physics for Scientists and Engineers II, Summer Semester 2009 15 Kirchhoff loop rule during switch-on process + -

16. Physics for Scientists and Engineers II, Summer Semester 2009 16 Kirchhoff loop rule during switch-on process + -

17. Physics for Scientists and Engineers II, Summer Semester 2009 17 Kirchhoff loop rule during switch-off process + -

18. Physics for Scientists and Engineers II, Summer Semester 2009 18 Measuring the time constant from switch-off process t I(t)

19. Physics for Scientists and Engineers II, Summer Semester 2009 19 Making sense of the time constant

20. Physics for Scientists and Engineers II, Summer Semester 2009 20 Back to flux and inductance calculations