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Magnetic Fields

Magnetic Fields. Magnetic forces only act on moving charges. The magnetic force (F B ) is perpendicular to the magnetic field (B measured in Teslas) and particles velocity (v) F= qvB or F=qvB(sin Ѳ ). In order to determine the direction of the magnetic force, you may use the right hand rule.

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Magnetic Fields

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  1. Magnetic Fields

  2. Magnetic forces only act on moving charges. • The magnetic force (FB) is perpendicular to the magnetic field (B measured in Teslas) and particles velocity (v) F= qvB or F=qvB(sinѲ)

  3. In order to determine the direction of the magnetic force, you may use the right hand rule. • Let’s watch a short video!!! (derek owens, magnetic force on moving charge)

  4. If the charged particle moves into a uniform magnetic field, perfectly perpendicular, the sideways force will provide centripetal motion. mv2/r = qvB

  5. Example 1: • A proton is observed to move along an arc of 32 cm when moving perpendicular to a magnetic field of 1.4 T. What is the momentum of the proton in kg m/s?

  6. If a particle is shot into an area which contains an electric field and the goal is to send it straight through (TV screen, capacitor) the electric field and the magnetic field must be equal. qE=qvB *notice charge cancels !! Wow!!

  7. Example 2: • A proton moves in the magnetic field B=0.5îT at a 45 angle degree with a velocity of 1.0 x 107 m/s. What is the magnetic force on the proton?

  8. Example 3: • A proton moves in the magnetic field B=0.5îT at a 180 degree angle with a velocity of 1.0 x 107 m/s. What is the magnetic force on the proton?

  9. Magnetic fields also affect current carrying wire. • Current carrying wire is actually amps in motion FB= I L B (sin Ө) or FB= I L B In order for a wire to levitate in a magnetic field, the force magnetic must counter the force gravitational

  10. Example 4: • What magnetic field strength and direction will levitate a 10cm long, 2.0g wire with a 1.5A current running through it?

  11. Examples 5 and 6: • A wire carrying a 2.0A current lies along the x axis. The current flows in the î direction. A 1.2T magnetic field makes a 30 degree angle with the xy plane. What is the force on a segment of 0.40m long?

  12. If the wire carrying the current is “looped” the wire may spin due to torque. T= μBsinθ = IABsinθ where A is area (Technically the Sum of the torques on each side of the loop!!)

  13. Example 7: • A square loop L=5.0cm on each side carries a 500 mA current. The loop is places in a magnetic field of 1.2 T. The axis of the loop is 30 degrees to the perpendicular field. What is the magnitude of the torque on the loop?

  14. A solenoid is a long current carrying wire that is “turned” X number of times in order to increase the magnetic field. B=μnI = μ(N/L)I

  15. Example 8: • A 2.0 cm diameter, 15 cm long solenoid is tightly wound from 1.0mm wire. What current is needed to generate a 3.0mT magnetic field inside of the solenoid?

  16. Ampere’s Law • Video time!! (Dan Fullerton)

  17. Homework: • Page 1034 # 1,3,5,6,12,14,40,41,49,57,58

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