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. +q qq If you release the electric dipole from rest, what will it do? 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. N S B-field If you release the magnetic dipole from rest, what will it do?

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 1.Place the compass on the edge of the table. It will twist so it is aligned with Earth’s magnetic field. 2.Connect a wire to a battery and lay the wire on top of the compass with the N-S axis of the compass. 3.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

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

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

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