Chapter 19. Magnetism. 1. Magnets. 2. Earth s Magnetic Field. 3. Magnetic Force. 4. Magnetic Torque. 5. Motion of Charged Particles. 6.

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1 Chapter 19 Magnetism 1. Magnets 2. Earth s Magnetic Field 3. Magnetic Force 4. Magnetic Torque 5. Motion of Charged Particles 6. Amperes Law 7. Parallel Conductors 8. Loops and Solenoids 9. Magnetic Domains 1

2 Magnets What is magnetism? What is a magnet? What is a magnetic pole? How many types of pole there are? Can single poles exist by themselves? How do you make a magnet? What is a induced magnet? Are all materials magnetic? What are hard and soft magnets? 2

3 Magnetic Fields What is a magnetic field? What symbol should I use for it? How is magnetic field produced by electric charges? Is magnetic field a vector? If yes how do I find the direction? 3

4 Magnetic Field Lines, sketch A compass can be used to show the direction of the magnetic field lines (a) A sketch of the magnetic field lines (b) 4

5 Magnetic Field Lines, Examples Bar Unlike poles Like poles 5

6 Earth s Magnetic Field What is the source? What is a dip angle? Dip angles for equator and poles True North and South Magnetic Reversal 6

7 Magnetic Force Where does it come from? How do I calculate it? What are the SI units What is a Gauss? Some examples 7

8 Right Hand Rule #1 How do I find the direction of the magnetic force? 8

9 Right Hand Rule - Example 1. Find the direction of force on a proton moving through a magnetic field (see problem 19.2 for figures). 2. Do the same for an electron. 9

10 Magnetic Force on a Current Carrying Conductor How do I calculate this force? 10

11 Torque on a Current Loop What is a current loop? Remind me, what is torque? How do I calculate this torque? What is magnetic moment? How do I calculate is from torque? 11

12 Example 1. A conductor carries a current of 15 Amps in the +x direction perpendicular to the B field. It experiences a force of 0.12 N/m in the y direction. Determine the direction and magnitude of the B field. 12

13 Example 1. Solve problem

14 Electric Motor 14

15 Force on a Charged Particle in a Magnetic Field What is the nature of this force? How do I calculate this force? What is a cyclotron equation? What if V is not perpendicular to B? 15

16 Example Mass Spectrometer 1. See examples 19.3 and

17 Example 1. A proton is accelerated through a electrostatic field of 2100 volts. It enters a magnetic field B=0.10T. Find the 1. Velocity of the proton 2. Change in Kinetic energy 3. Cyclotron radius 17

Hans Christian Oersted 1777 1851 Best known for observing that a compass needle deflects when placed

18 Hans Christian Oersted Best known for observing that a compass needle deflects when placed near a wire carrying a current First evidence of a connection between electric and magnetic phenomena 18

19 Magnetic Fields Long Straight Wire If a magnetic field can produce current, can a current produce magnetic field? How do I calculate this field? How do I find the direction of this magnetic field? 19

André-Marie Ampère 1775 1836 Credited with the discovery of electromagnetism

20 André-Marie Ampère Credited with the discovery of electromagnetism Relationship between electric currents and magnetic fields Mathematical genius evident by age 12 20

21 Ampère s Law What is Amperes law? How do I use it? How about an example? 21

22 Example 1. Find the magnetic field at point P shown in the diagram. 22

23 Example 1. Find the magnetic field at a distance of P from each wire shown in the diagram. 23

24 Magnetic Force Between Two Parallel Conductors How do I calculate this force? What is the final situation? 24

25 Example 1. Two parallel wires are 10 cm apart, and carries a current of 10 A. 1. If the current are in the same direction, find the force per unit length exerted by one of the wires on the other. 2. Repeat the problem with the current in opposite direction. 25

26 Defining Ampere and Coulomb The force between parallel conductors can be used to define the Ampere (A) If two long, parallel wires 1 m apart carry the same current, and the magnitude of the magnetic force per unit length is 2 x 10-7 N/m, then the current is defined to be 1 A The SI unit of charge, the Coulomb (C), can be defined in terms of the Ampere If a conductor carries a steady current of 1 A, then the quantity of charge that flows through any cross section in 1 second is 1 C 26

27 Magnetic Field of a Current Loop How do I calculate it? 27

28 Magnetic Field of a Solenoid What is a solenoid? How do I calculate its magnetic field? What does it field look like? 28

29 Magnetic Field in a Solenoid, 3 The field lines of the solenoid resemble those of a bar magnet 29

30 Magnetic Field in a Solenoid from Ampère s Law How do I apply Amperes law? 30

31 Example 1. What current is required in the windings of a long solenoid that has 1000 turns uniformly distributed over a length of 0.40 m in order to produce a magnetic field of magnitude 1.0 x 10-4 at the center of the solenoid? 31

32 Magnetic Effects of Electrons Hey can we talk about electrons, since they are charge particles, they spin and orbit the nucleus of the atom, they got to have magnetic 32

33 Magnetic Effects of Electrons Domains Ferromagnetism Domains Permanent magnets 33

Torque on a Current Loop

Today Chapter 19 Magnetism Torque on a current loop, electrical motor Magnetic field around a current carrying wire. Ampere s law Solenoid Material magnetism Clicker 1 Which of the following is wrong?