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Physics 7C SS1 Lecture 8: Electricity & Magnetism

Physics 7C SS1 Lecture 8: Electricity & Magnetism. Magnetism: RHR 1 & 2 Light as EM wave Polarizers. What’s left?. 2 Lectures 1 Quiz 4-5 DL Optional review lecture A 1hr15min final exam. v. B. q. F. Field Model of Magnetism.

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Physics 7C SS1 Lecture 8: Electricity & Magnetism

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  1. Physics 7C SS1Lecture 8: Electricity & Magnetism Magnetism: RHR 1 & 2 Light as EM wave Polarizers

  2. What’s left? • 2 Lectures • 1 Quiz • 4-5 DL • Optional review lecture • A 1hr15min final exam

  3. v B q F Field Model of Magnetism • A source moving charge creates a magnetic fields in a direction given by RHR1. • Another moving charge, placed in a magnetic field, experiences a magnetic force • Magnitude given by F=qvBsin • Direction of force given by RHR2

  4. Experiments with magnets and compasses • Magnets have poles that repel and attract N N S S N S S N

  5. Experiments with magnets and compasses • Magnets attract one end of a compass needle and repel the other. S N

  6. Iron fillings align with the magnetic field. Dipole Field:

  7. Cutting a magnet • Slicing a magnet in half results in two weaker magnets, each with a north and south pole.

  8. What happens with a compass is brought near a charged rod? • South pole is attracted to rod • North pole is attracted to rod • Neither pole is attracted to rod

  9. What happens with a compass is brought near a charged rod? • South pole is attracted to rod • North pole is attracted to rod • Neither pole is attracted to rod

  10. Which rule is used to find the magnetic field at point A? • RHR1 • RHR2 • LHR1 • You can use either hand--just be sure to point your thumb in the direction of the current and curl your fingers to find B! A I

  11. Which direction is the magnetic field at point A? • Left • Right • Up • Down • Into screen • Out of screen • Away from wire • Toward wire • Something else A I

  12. Which direction is the magnetic field at point A? • Left • Right • Up • Down • Into screen • Out of screen • Away from wire • Toward wire • Something else A I

  13. Which direction is the magnetic field at point B? • Left • Right • Up • Down • Into screen • Out of screen • Away from wire • Toward wire • Something else B I

  14. Which direction is the magnetic field at point C? • Left • Right • Up • Down • Into screen • Out of screen • Away from wire • Toward wire • Something else C I1 I2 You may assume I1=I2

  15. Which direction is the magnetic field at point C? Btot • Left • Right • Up • Down • Into screen • Out of screen • Away from wire • Toward wire • Something else C I1 I2 You may assume I1=I2

  16. Magnetic Force • Suppose a large magneticfield points downward at every point in the room. What direction is the force on a positive particle traveling along the chalkboards, to your left? Into the board Out of the board Left (along particle path) Right (opposite path) Down Up No Force v B q F = qvBsinq, where q is the angle between B and v

  17. Magnetic Force • Suppose a large magneticfield points downward at every point in the room. What direction is the force on a positive particle traveling out of the board, to the back of the room? Into the board Out of the board Left Right Down Up No Force v B q F = qvBsinq, where q is the angle between B and v

  18. Magnetic Force • Suppose a large magneticfield points downward at every point in the room. What direction is the force on a positive particle traveling upward, toward the ceiling? Into the board Out of the board Left Right Down Up No Force v B q F = qvBsinq, where q is the angle between B and v

  19. Magnetic Force • Suppose a large magneticfield points downward at every point in the room. What direction is the force on a positive particle traveling upward, toward the ceiling? Into the board Out of the board Left Right Down Up No Force v B q F = qvBsinq, where q is the angle between B and v

  20. Using both RHRs • Look at the demonstration. Notice how the wires are bending. If you know the current in the left wire flows upward, which way is the current in the right wire? • Up • Down • Either • No current

  21. Switching Gears: Rethinking Light • What “waves” in light? • What propagates?

  22. Image from http://www.monos.leidenuniv.nl/smo/index.html?basics/light.htm

  23. A vertical wave traveling through a vertical fence passes unimpeded. The second fence also lets the wave pass. If we place the second fence with horizontal slats, the vertical vibrations cannot pass through the fence. Image from http://www.glenbrook.k12.il.us/GBSSCI/PHYS/CLASS/light/u12l1e.html

  24. Image from http://www.lbl.gov/MicroWorlds/teachers/polarization.pdf

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