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Ampere’s Law

Ampere’s Law. Physics 102 Professor Lee Carkner Lecture 18. Currents and Magnetism. It is also true that moving charged particles produce magnetic fields Serious magnetic fields are produced by currents What is the magnitude and direction of these fields?.

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Ampere’s Law

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  1. Ampere’s Law Physics 102 Professor Lee Carkner Lecture 18

  2. Currents and Magnetism • It is also true that moving charged particles produce magnetic fields • Serious magnetic fields are produced by currents • What is the magnitude and direction of these fields?

  3. Magnetic Field from a Current in a Wire • Needle deflected tangentially to the wire cross section • How can we find the direction and magnitude of the B field for any situation?

  4. Grasp the wire with your thumb in the direction of the current and your curled fingers indicate the direction of the field Right Hand Rule Revisited

  5. Ampere’s Law • To find the magnitude of the B field we use Ampere’s law • The sum of the product of DL and B around the entire path is equal to m0I • Where m0 = 4p X 10-7 T m /A and is called the permeability of free space S BDL = m0I

  6. B Field for a Wire S BDL = m0I or B SDL = m0I • Since B is the same everywhere around the circle B 2pr = m0I B = m0I/2pr • Magnetic field a distance r from a long straight wire with current I

  7. Force on Two Parallel Wires • The B field then will exert a force on the other wire B = m0I/2pd • For two wires of equal length but different currents: F = m0I1I2L/2pd

  8. Can apply the right hand rule all the way around Loop acts as a bar magnet Magnetic Field: Loop

  9. What happens if you stack several loops up? You produce a solenoid Field inside the solenoid is strong and uniform (far from the ends) Magnetic Field: Solenoid

  10. Electromagnet • We can write an expression for the solenoid magnetic field: B = m0nI • If you put a piece of iron in the center you get an electromagnet

  11. Next Time • Read: 21.1-21.2 • Homework: CH 21 P: 1, 2 CH 20 P: 38, 50

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