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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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**Physics 7C SS1Lecture 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 • 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**Experiments with magnets and compasses**• Magnets have poles that repel and attract N N S S N S S N**Experiments with magnets and compasses**• Magnets attract one end of a compass needle and repel the other. S N**Cutting a magnet**• Slicing a magnet in half results in two weaker magnets, each with a north and south pole.**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**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**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**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**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**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**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**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**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**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**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**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**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**Switching Gears: Rethinking Light**• What “waves” in light? • What propagates?**Image from**http://www.monos.leidenuniv.nl/smo/index.html?basics/light.htm**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**Image from**http://www.lbl.gov/MicroWorlds/teachers/polarization.pdf

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