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EM3 Electromagnetism

EM3 Electromagnetism. Electromagnetism. Forcing a wire through a magnetic field produces (generates) a current in the wire Example: Generator Converts mechanical energy into electrical energy. generators.

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EM3 Electromagnetism

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  1. EM3 Electromagnetism

  2. Electromagnetism • Forcing a wire through a magnetic field produces (generates) a current in the wire • Example: Generator • Converts mechanical energy into electrical energy

  3. generators • Generators spin a bundle of wire attached to a motor through magnets causing current or electricity to be produced

  4. Electromagnetic induction (induced current) • Electromagnetic induction- a current is produced in a wire by passing a magnet near it • The magnetic field lines (flux) crossing the wire cause the electrons in the wire to move (electricity)

  5. Electromagnetic induction • Force is greatest when the charge moves perpendicular to the magnetic field • At other angles the force is less • The force is 0 when the charge moves parallel to the magnetic field

  6. Magnetic flux • Magnetic Flux ( Φ ) - The # of magnetic field lines passing through a given area • Magnetic Flux( Φ ) =BA

  7. Magnetic Flux • Where is the greatest concentration of magnetic flux lines? • Near the poles (ends)

  8. Magnetic Field • A current carrying wire placed in a magnetic field experiences a force • Example: Motors • Converts electrical energy into mechanical energy

  9. Second right hand rule • 1. Keep hand flat • 2. Thumb in the direction of the current • 3. Fingers in the direction of the magnetic field • 4. Palm in direction of the force • All are perpendicular to each other

  10. What determines the strength of the force? • 3 factors affect the magnitude of the force on a current-carrying wire placed in a magnetic field • 1. Strength of the magnetic field • 2. Amount of current (velocity) • 3. Length of the wire

  11. Mathematically • F=B I l • F=Force (N) • B=magnetic field strength (N/am) • I=Current in wire (a) • l=Length of the wire perpendicular to the field (m)

  12. example • A segment of wire .040 m long is perpendicular to the magnetic field inside a solenoid. When a current of 3.0 amps flows through the wire, it takes a force of 0.020 Newtons to balance the wire. What is the magnetic field inside the solenoid. F= B I L .020N = B (3.0 amps) (.040m) B = .17 N / amp m

  13. charge • The formula can also be written for any single charge moving through a magnetic field • F=Bqv • F=Force (N) • B=Magnetic field strength (N/am) • q=charge (C) • v=velocity of charge (m/s)

  14. When the charge is an electron • When not just any charge, but an electron • F=Bev • e=charge for an electron (1.6 X 10^-19 C)

  15. Example • An electron moves through a magnetic field of .20 N/Am at a speed of 300,000 m/s. What is the force on the charge due to this field? F = B e v F = .20 N/Am (1.6 x 10-19 C)(300,000 m/s) F = 9.6 x 10-15 N

  16. Voltage • Voltage-Energy needed to move a charge

  17. Motors • Helps explain how motors work • Motors convert electrical energy into mechanical energy

  18. Faraday’s law • Faraday’s Law- Voltage (current) induced in a wire is proportional to the rate of magnetic flux cutting across the wire • What happens when you increase voltage? • Increase magnetic flux (the # of magnetic field lines/area)

  19. Relative motion • Relative Motion-The movement of one object with respect to another object

  20. Lenz’s Law • Lenz’s Law-The current induced in a wire is in such a direction that its magnetic field opposes the changing field that induced it

  21. Equation • Emf = -B l v • Emf=electromotive force (volts) • B=Magnetic Field Strength • l=length of wire • v=velocity

  22. Example • A wire of length 50 cm is moving at a speed of 2.0 m/s perpendicular to a magnetic field of 0.75 N/A m. What emf is induced in the wire? Emf = -B l v Emf = - (.75 N/A m) (.50 m) (2.0 m/s) Emf = 0.75 Volts

  23. transformers • Transformers- A device to increase or decrease voltage • http://phet.colorado.edu/en/simulation/faraday

  24. transformers • N1/N2 = V1/V2 • N=number of turns of wire • V=voltage (volts)

  25. Transformers: example • If the primary coil having 5 turns of wire contains 20 volts, what is the voltage in the secondary coil having 10 turns? N1/N2 = V1/V2 5 / 10 = 20 / V2 V2 = 40 Volts

  26. Bell ringer • 1. A segment of wire 25 cm long is in a magnetic field of .75 N/A m. The force on the wire is 0.30 N. What is the current flowing through the wire? • 2. A charge (2.3 X 10^-15 C) moves through a magnetic field at 225,000 m/s. What is the magnetic field strength if the force is 4X10^-4 N?

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