1. Magnetic Field Physics 102 Professor Lee Carkner Lecture 17

2. PAL # 16 RC Circuits  From left loop: I 2 = (15 – 11I 1 )/7.5 =  From big loop: I 3 = (15 –11I 1 )/18.2 =  Put in junction rule: I 1 = 2 – 1.5I 1 + 0.82 – 0.6I 1  3.1I 1 = 2.82 or I 1 =  Put in loop rules:  Junction rule:  I 1 = I 2 + I 3  Loop rule (left loop):   Loop rule (big loop):  15 – 6.2I 3 – 12 I 3 –11I 1 = 0  I1I1 I2I2 I3I3

3. Electricity and Magnetism   Certain metals   Both of these forces are due to the same fact:   The reverse is also true:   Both electricity and magnetism are related to charge

4. Dipolar Field

5. Magnets  Magnets are dipolar   No magnetic monopoles  Like poles repel, opposite poles attract   The north pole on one end and the south on the other   Magnetic field lines go from north to south

6. No Magnetic Monopoles

7. Like Repel, Opposites Attract

8. Magnetic Domains   The moving charges in a magnet are spinning electrons   Regions where the electron spins reinforce each other   May be permanent or temporary depending on the material and the strength of the external magnetic field

9. Vectors   The field produces a force (F) on a moving charged particle   All three quantities are vectors   What is the relationship between them?  i.e., if the B field points one way and the charge is moving another way, what is the direction of the force?

10. Right Hand Rule   If v is your straight fingers, and B is your curled fingers, F is your thumb F v B

11. Vector Conventions  The force on a negative particle is opposite that of a positive one   Vectors going into the page are represented with a cross (X), vectors going out of a page are represented with a dot (  )

12. Magnetic Force  The magnetic force depends on 4 things:   The magnitude of the charge (q)   The angle between the v and B vectors (  )  The force can be written as: F = qvB sin 

13. Magnetic Field  We can use the expression for the force to write an expression for the magnetic field:  The SI unit for the field is the tesla (T)   1 T = 10000 G   Earth’s magnetic field ~ 1 G

14. Today’s PAL  Suppose a beam of electrons is pointed right at you  What direction would the magnetic field be in to produce the maximum deflection in the up, down, right and left directions?  What two direction for B would produce the minimum deflection? Why?

15. The Earth’s Magnetic Field   Charges move in the Earth’s liquid core   The north pole of the compass points north, the south pole of the compass points south 

16. Earth as a Magnet

17. Navigation   The magnet makes an angle with the rotation axis   A compass does not point to geographic north  You need to know the offset between the magnetic and geographical direction (called the declination)

18. Jupiter’s Magnetosphere

19. Aurora on Jupiter

20. Planets and Magnetism  A planet will have a magnetic field if:    The planet’s magnetic field interacts with charged particles streaming off of the Sun known as the solar wind  This interaction region is known as the magnetosphere 

21. Next Time  Read 20.2-20.6, 20.9  Homework: Ch 20, P 1, 9, 15, 27  Exam #2 next Friday  Same format as Exam #1  Covers Chapters 16-20