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Understanding Electric & Magnetic Dipoles: Their Behavior & Interactions

Learn about electric and magnetic dipoles, their responses in fields, and behaviors when released. Explore compasses, magnetic monopoles, current-induced fields, and the principles governing their actions.

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Understanding Electric & Magnetic Dipoles: Their Behavior & Interactions

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  1. CH 22-1

  2. Electric Dipole An electric dipole is made of equal magnitude, opposite charges. In an electric field, an electric dipole will twist so that it aligns with the E-field with the +q toward the E-field and the -q opposite the E-field. If you release the electric dipole from rest, what will it do? +q q E-field

  3. Magnetic Dipole A compass needle is a magnetic dipole. It will twist so that it is aligned with the magnetic field, with the N side of the needle toward the magnetic field and the S side away from the magnetic field. If you release the magnetic dipole from rest, what will it do? N S B-field

  4. No magnetic monopoles If you break a magnetic dipole in half, how will it respond to a magnetic field? It still twists just like before! Thus, if you break a magnetic dipole in half, you will still have a magnetic dipole. You cannot have just a N pole, without also having a S pole. There are no magnetic monopoles!

  5. Compass A compass points in the direction of the net magnetic field.

  6. Magnetic field can be created by current in a wire Place the compass on the edge of the table. It will twist so it is aligned with Earth’s magnetic field. Connect a wire to a battery and lay the wire on top of the compass with the N-S axis of the compass. Which way does the needle twist and why? 4. Disconnect the wire, what happens to the needle? 5. How do you know that current produces a magnetic field?

  7. Direction of magnetic field due to current -- The Right-hand Rule

  8. Poll

  9. Poll

  10. Poll

  11. Magnetic field due to moving electron The magnetic field due to a moving electron is in the opposite direction and is given by the left-hand rule.

  12. Poll

  13. Poll

  14. Magnetic field due to a long wire The magnetic field at a distance r from a long wire with current I has a magnitude

  15. Magnetic field due to current in a loop What is the direction of the magnetic field at each of the points shown, due to current in the loop?

  16. Magnetic field due to current in a loop, along the axis of the loop battery not shown

  17. Magnetic field diminishes with distance from the loop

  18. Loop of current acts like a magnetic dipole -- we call it an electromagnet S N

  19. Poll What is the direction of the magnetic field along the axis of the loop? 1. downward 2. upward I

  20. Poll Which is the N side of the electromagnet? 1. the top 2. the bottom I

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