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PHYSICS 51 CH 28

PHYSICS 51 CH 28. Homework #8: Magnetic Fields. Read Ch. 27.1 - 27.7 We will talk a bit in class about sections 8 and 9 also Do Exercises : Ch 27, #1, # 16, # 42, #46, #74 Due: Thursday April 3. 2014. Chapter 28: Sources of Magnetic Fields. Biot-Sevart Law

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PHYSICS 51 CH 28

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  1. PHYSICS 51 CH 28

  2. Homework #8: Magnetic Fields • Read Ch. 27.1 - 27.7 • We will talk a bit in class about sections 8 and 9 also • Do Exercises :Ch 27, #1, #16, #42, #46, #74 • Due: Thursday April 3. 2014

  3. Chapter 28: Sources of Magnetic Fields • Biot-Sevart Law • Calculate Magnetic field from current elements • Wires creating magnetic fields • 1-D • 2-D • Ampere’s Law (Thursday) • Calculate Magnetic field from symmetry of the problem

  4. A moving charge causes B field

  5. A current in a wire causes B field

  6. B field due to Wire

  7. B field due to long straight wire Magnitude B = oI/2R Direction Right hand rule

  8. Example of Mag. Field calculation A wire carries 1.0A of current. At what distance does the magnetic field from the wire equal the Magnetic field strength of the earth (ME = 0.5 x 10-4T) Physical constant o = 4 x 10-7 Tm/A

  9. Multiple wires in 1-D P x There are two wires, one with a current of 1.0A going into the page and the other has a current of 1.0A out of the page. The wires are 2.0 cm and 1.0 cm from P Calculate the magnetic field at P

  10. Multiple wires in 2-D a) b) There are 4 wires arranged in a square. For each case indicate the direction of the magnetic field at the center of the square

  11. 2 wires interact with a net force 1st wire creates field Field interacts with Current In 2nd wire Same direction Attract Opposite direction Repel

  12. y #3 = out of page = onto page x #2 #1 Interaction of 3 wires What is the force/length on wire #1. Each wire carries a current I0, they are on a grid of distance d

  13. Ampere’s Law • Allows us to use the symmetry of the situation to calculate the magnetic field • 4 Steps • Draw Amperian Loop • Direction matches right hand rule • Calculate the line integral around the loop • Calculate the enclosed current • Set current = integral and solve for B

  14. Ampere’s Law: Examples • Single wire ( me ) • Conducting cable ( me ) • Cylindrical Cable ( you )

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