1. Finishing 21, Starting 22 What a revolting development!

2. Watt’s Happnin? We finish chapter 21 – read it ALL! Start reading the next chapter as well. Exam #3 at conclusion of chapter 21. This week we discuss induction and do some experiments and activities. We look at Murphy’s Law comes from. You will have another quiz opportunity on Friday. Watch for another WebAssign coming soon to a neighborhood theater near you.

3. FROM LAST TIME : A LOOP OF WIRE center of circular loop

4. Example 10 Finding the Net Magnetic Field A long straight wire carries a current of 8.0 A and a circular loop of wire carries a current of 2.0 A and has a radius of 0.030 m. Find the magnitude and direction of the magnetic field at the center of the loop.

5. 21.7 Magnetic Fields Produced by Currents

6. Conceptual Example : The Net Force That a Current-Carrying Wire Exerts on a Current Carrying Coil Is the coil attracted to, or repelled by the wire?

7. The field lines around the bar magnet resemble those around the loop. Remember?

8. A SOLENOID Interior of a solenoid number of turns per unit length

9. Consider a wire and the expression AMPERE’S LAW

10. AMPERE’S LAW CAN BE GENERALIZED For any current geometry that produces a magnetic field that does not change in time, net current passing through surface bounded by path

11. 21.8 Ampere’s Law GOING BACKWARDS AGAIN Use Ampere’s law to obtain the magnetic field.

12. Far away – B=0 If solenoid is long enough, B is perpendicular to side.

13. So far There are natural magnets Magnets effect moving charges Moving charges (currents) create magnetic fields ▫In some cases, we can compute these via Ampere’s Law Magnetic fields produce forces on current carrying conductors What will a changing magnetic field do to a wire or a coil??Question: What will a changing magnetic field do to a wire or a coil??

14. Electromagnetic Induction

15. INDUCTION The movement of the magnet closer to the coil increases the “amount of magnetic field” going through the coil. This causes a current to develop in the coil. This process is called INDUCTION.

16. Magnetic Flux “Amount of Magnetic Field” needs to be defined: Magnetic Flux

17. 22.3 Magnetic Flux GENERAL EXPRESSION FOR MAGNETIC FLUX

18. 22.3 Magnetic Flux

19. GRAPHICAL INTERPRETATION OF MAGNETIC FLUX The magnetic flux is proportional to the number of field lines that pass through a surface.

20. 3/1/2016Induction 20

21. The Magnetic Flux Going Through The Loop: 21 Add up all of these pieces that are INSIDE the loop.

22. Changing  3/1/2016Induction 22 Change any or all of the ▫Bi▫Bi ▫   ▫i▫i ▫Change the SHAPE of the loop ▫Change the ANGLE that the loop makes with the magnetic field (subset of above) And the Flux will change!

23. Changing the flux through the loop will change the current. But what way will the current actually flow?

24. We will now enter The Strange World of Dr. Lentz

25. The Galvanometer Be nice to ME

26. In this experiment you will Work with 2 coils Change the flux in a number of ways. Decide HOW you are changing the flux Looking at the DIRECTIONS of the induced currents Observe the hideous Gauss’s Law in action. ▫Also known as Murphy’s Law!