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W7D2 Magnetism

W7D2 Magnetism. October 5, 2011. This week. Monday Finish Capacitor Activity Dielectric in Capacitors Magnetism, Intro. Wednesday Magnetism Friday Quiz Magnetism. Monday More Magnetism Wednesday EXAMINATION #2 Potential Magnetism – as far as we get

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W7D2 Magnetism

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  1. W7D2 Magnetism October 5, 2011

  2. This week • Monday • Finish Capacitor Activity • Dielectric in Capacitors • Magnetism, Intro. • Wednesday • Magnetism • Friday • Quiz • Magnetism • Monday • More Magnetism • Wednesday • EXAMINATION #2 • Potential • Magnetism – as far as we get • Some old stuff might be necessary. • After Exam – continue with new material DONE

  3. From the textbook….. If you want some insight into how this comes about, check the website.

  4. The Right Hand Rule Try not to hurt yourself when these vectors are in difficult orientations!

  5. Can you do this? A vector of magnitude 5 lies along the x axis, and a vector of magnitude 10 lies in the xy plane, 30 degrees from the x axis (see the figure). What is the magnitude and direction of the cross product C x D?

  6. Magnets • Made of mysterious materials (lodestone???) • Each Magnet has a North and South pole. • Break a magnet between the N and S pole and you wind up with two magnets, each with a N and S pole. • Magnets produce magnetic fields. (More on that later) • Moving charges also create magnetic fields. This is the next topic that we will discuss and explore now that you have done the experiment on this.

  7. Remember Coulomb? Source Charge Unit Vector Vector Inverse Square Law

  8. Biot-Savart Law Magnetic Field Intensity Tesla Source Current Element Inverse Square q Magnetic Permeability of Space

  9. B is a VECTOR (Unit – Weber) unit vector

  10. B Activity

  11. Magnetic Field Around a Wire • DISCUSSION • Does this agree with your last experiment? Which kind of current??? • Does this agree with B-S?

  12. Let’s Discuss Current • Water current flows down hill. • Gravitational Field is pulling it down. • The flow is from high to low gravitational potential. • It is hard to swim against the current. • Electric Current flows in a similar way – from high to low electric potential (Voltage).

  13. One Charge q is NOT the norm .. A CURRENT is! This is NOT the norm

  14. Electric Current-1 • The amount of CHARGE that crosses a cross-section of a wire such as this in ONE SECOND is defined as a current of one Ampere.

  15. Electric Current-2 • The electron current flows against the Electric Field. • The electric field exists because a battery (or something else) creates the electric field. • The conventional current flow is in the direction of the electric field. • Only the negative electrons actually move. The positive (+) charges remain stationary.

  16. Electric Current-3 • The electrons “drift” at a drift velocity v. • In time Dt they drift a distance vDt. • The volume of electrons that flow in that time is AvDt. • Let n be the number of electrons that can move per unit volume. A

  17. Electric Current-4 A IMPORTANT !

  18. Electric Current Electron Current = Number of electrons crossing the area/second Electron Current Conventional Current Conventional Current = Positive charge crossing area/second

  19. Which current is this equation for? IMPORTANT !

  20. NO BOOKS – Just material from this lecture!! Break a long wire carrying a current I into a bunch of small segments. Express the magnetic field DB at point A in terms of the current element Dl. Replace the equation above with this expression.

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