2. Third exam Thursday, April 23 105, 107 Heldenfels 7 pm – 8 pm

3. The force on a charge q moving with a velocity The magnitude of the force

4. left-hand rule right-hand rule

5. Small peace of wire

6. Ampere’s Law The field produced by an infinite wire

7. Biot-Savart Law Infinitesimally small element of a current carrying wire produces an infinitesimally small magnetic field (Also called Ampere’s principle) is called permeability of free space

8. Faraday’s Law of Induction The induced EMF in a closed loop equals the negative of the time rate of change of magnetic flux through the loop

11. Test 3 results Average 77 Median 84 9 perfect scores >90>80>70>60>50<50 39 13 10 9 11

12. In the circuit below, suppose the switch has been in position A for a very long time. If it is then switched to B at t=0, find the current as a function of time. A B + _ L R V

13. Make your own MOTOR! All you need is a battery, a nail, a small magnet, and a wire (foil works better) http://en.wikipedia.org/wiki/Homopolar_motor

14. General Atomics is developing a full-scale, 36.5-megawatt, 120- rpm superconducting DC homopolar motor for ship propulsion. Significantly quieter, smaller, and lighter than AC motors More efficient than the AC motor systems Control is more straightforward and simpler than the AC motor systems Suited to simpler and less costly ship electrical distribution architectures http://atg.ga.com/EM/defense/dc-motor/index.php

15. Magnetic Materials Diamagnetism: The magnetic field caused by current loops is always opposite in the direction to that of the external field. Paramagnetism: When such a material is placed in a magnetic field, the field exerts a torque on each magnetic moment,. These torques tend to align the magnetic moments with the field. In this position, the directions of the current loops are such as to add to the externally applied magnetic field. Ferromagnetism: iron, nickel.. Magnetic moments line up parallel to each other in magnetic domains even without external field. Without field they are randomly oriented. When field is applied, the domains tend to orient themselves parallel to the field.

16. Water NitrogenOxygen Boils Freezes 100 °C (212 F)-196 °C (-322 F)-183 °C (-297 F) 0 °C (32 F) -210 °C (-346 F) -223 °C (-369 F) Our air is ¾ Nitrogen and ¼ Oxygen

17. 1908- liquefied helium produced First discovered in mercury by Kamerlingh-Onnes in 1911. Critical temperature 4.21K. Nobel Prize in 1913. Superconductivity

18. High-T c Superconductivity Liquid nitrogen temperature 77 K Complex ceramic materials were discovered in 1986. They exhibit superconductivity at much higher temperatures – above LN temperature! Muller and Bednortz, Nobel Prize 1987

19. Superconductivity Kamerlingh-Onnes 1911

21. Meissner effect and magnetic levitation

22. Type I superconductor Type II superconductor

23. Vortices