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Electromagnetic Induction

Physics 30S. Electromagnetic Induction. Electromagnetism. What is Electromagnetism?. A changing magnetic field creates an electric field A changing electric field creates a magnetic field Basis for electricity generation, transmission, most uses and applications. Maxwell’s Equations.

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Electromagnetic Induction

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  1. Physics 30S Electromagnetic Induction

  2. Electromagnetism

  3. What is Electromagnetism? • A changing magnetic field creates an electric field • A changing electric field creates a magnetic field • Basis for electricity generation, transmission, most uses and applications

  4. Maxwell’s Equations • Complicated, but in essence: • Electric fields and magnetic fields are one phenomena: an electromagnetic field • United concepts of electricity and magnetism into 4 equations James Clerk Maxwell June 13 ,1831 – November 5, 1879

  5. Michael Faraday • Faraday was a great researcher • Intuitive knowledge about electricity and magnetism • Performed many experiments which paved the way for an understanding of electromagnetism • Primitive motor September 22, 1791 – August 25, 1867

  6. Hans Christian Oersted • Oersted made one of the first electricity/magnetism insights all because of a messy desk • Current carrying wire caused compass needles to divert • Oersted’s basic principle of electromagnetism: moving electric charges produce a magnetic field August 14,1777 – March 9, 1851

  7. Field around a Current Carrying Wire • Current through a wire creates a circular magnetic field; weakens with distance • Right Hand Rule 1: • Point thumb in the direction of the current • Make a fist • Fingers show direction of magnetic field • Magnitude of field: B is the magnetic field (T) I is the current (A) r is the distance from the wire (m)

  8. Right Hand Rule 1 • Point your thumb in the direction of current flow • Fingers wrap to show direction of the magnetic field

  9. Visualizing the Magnetic Field around a Wire • Point your thumb with the current • Curl your fingers to determine the direction of the field

  10. What is ? • Permeability of free space • 4π x 10-7 Tm/A • Physical constant • Permeability relates the ability of the medium to induce a magnetic field • Inductance

  11. Notation • Current • Coming out of the screen • Going into the screen • Meant to visualize an arrow

  12. Example1 Right Hand Rule 1 Add arrows to show the direction of the magnetic field

  13. Solution

  14. Example 1: Calculating Field a) What is the strength of the magnetic field 15 cm away from a wire carrying 75 A? B = 1.0 x 10-4 T b) At what distance is the strength of the magnetic field 1.5 x 10-5 T? r = 1.0 m

  15. Example 2: Calculating Field a) How much current is a wire carrying if the magnetic field is measured to be 3.03 x 10-3 T at 0.500 meters away? I = 7580 A b) What is the strength of the magnetic field 1.50 m from the wire? B = 1.01 x10-3 T

  16. Homework • 3. Magnetic Fields Homework Handout

  17. Force on a Current Carrying Wire • Current carrying wires experience a force in an external magnetic field • Right Hand Rule 2: • Make an L shape with your hand • Thumb points in the direction of the current • Fingers point in the direction of the magnetic field • Palm shows the direction of the force • Magnitude of the Force: B is the magnetic field (T) I is the current (A) l is the length of the wire (m) Θ is the angle between the magnetic field and the wire (not in the text)

  18. Example 1 Right Hand Rule 2 What direction is the force on the wire? Solution: Into the screen

  19. Example 1: Calculating Force A 25cm wire in a motor carrying 15 A of current is in a magnetic field of 0.2T. What will be the force on the wire, assuming that the wire and magnetic field are perpendicular? FB = 0.08 N

  20. Example 2: Calculating Force What length of conductor, running at right angles to a 0.033 T magnetic field and carrying a current of 20.0 A, will experience a force of 0.10N? I = 0.15 m

  21. What about Charged Particles? • Magnetic fields exert a force on moving electrical charges, including charged particles • What might the formula be?

  22. Example 1: Moving Particles • An electron is shot through a cathode ray tube TV at 5.0 x 105 m/s, perpendicular to the direction of the field. If the force acting on the particle is 2.0 x 10-15 N and the length of the tube is 10 cm, what is the strength of the magnetic field? • B = 0.025 T

  23. Example 2: Moving Particles • An alpha particle (He2+) is shot through a magnetic field at 3.33 x 106 m/s, perpendicular to the direction of the field. If the magnetic field strength is 1.5 x 10-4T, what is the magnitude of the force acting on the particle? • F = 1.6 x10-16 N

  24. Homework - Textbook • Pg.569 • Force on a Wire: #7-9 • Pg. 574 • Force on a Moving Particle: #10-11

  25. Defining Magnetic Field • Magnetic field hasn’t been defined qualitatively • Magnetic field is a force per unit current element • Electromagnetism is needed

  26. Solenoid Picture • A solenoid is our first electromagnet • Magnet caused by electricity

  27. Solenoids • A solenoid is a coiled wire • Contains many loops • Magnetic field of each loop sums to make the magnetic field of the solenoid • http://webphysics.davidson.edu/Applets/BField/solenoid.html • Capable of producing strong magnetic fields • Right Hand Rule 3: • Coil fingers with the direction of current • Thumb points in the direction of magnetic north • Magnetic field created is similar to a bar magnet

  28. Right Hand Rule 3: Solenoids • Right Hand Rule 3: • Coil fingers with the direction of current • Thumb points in the direction of magnetic north

  29. Diagram of a Solenoid’s Field Where are the North and South Poles?

  30. Homework • Calculating Magnetic Forces Exercises Handout

  31. Lab Experiment • Lab Manual 24.1

  32. Electric and Magnetic Fields

  33. Research an Electromagnet • Pick from one among the list. • Research about how it works • Specifically, where is electromagnetism involved and how does it make the device function? • 2 minute presentation at the end of class explaining the device to the class • Include multi-media if possible! • Questions?

  34. The List • Speakers • Cathode Ray Tubes/Television • Alarms • Electromagnets for Lifting Steel • Generators • Electric motors • Maglev trains

  35. Technologies/Electromagnets • Primitive motor • Make the Motor • Generator • Reverse motor • Electromagnet • How do you think this works? • Speakers • http://electronics.howstuffworks.com/speaker5.htm • Cathode Ray Tube • Alarm/bell • Maglev trains • http://player.discoveryeducation.com/index.cfm?guidAssetId=6581C80B-C521-4467-9A8A-E56533E3FC83&blnFromSearch=1&productcode=US

  36. Summary of Hand Rules • Right Hand Rule 1: • Point thumb in the direction of the current • Make a fist • Fingers show direction of magnetic field • Right Hand Rule 2: • Make an L shape with your hand • Thumb points in the direction of the current • Fingers point in the direction of the magnetic field • Palm shows the direction of the force • Right Hand Rule 3 (Solenoids): • Coil fingers with the direction of current • Thumb points in the direction of the magnetic field

  37. The Plan! • Day 1 -2: What is Electromagnetism, Maxwell, Oersted, Field around a wire, • Up to slide 16 • Day 2: Force around a wire, Force on moving particles • Up to slide 24 • Day 3: Definition of Magnetism, Solenoids, In-class work • Up to slide 26 • Solenoid example • Day 4: Lab Experiment • Day 5: Electromagnet applications research, summary of right hand rules (Friday) – Gr. 11 up to here • Up to Slide 36 • Day 6: Review • Day 7 Test

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