CH 23-1

1. CH 23-1

2. Another way of doing the Right-hand Rule for Magnetic Field due to a loop Face the loop. If current flows counterclockwise, then the magnetic field along the axis is directed out of the loop. If current flows clockwise, then the magnetic field along the axis flows into the the loop.

3. Magnetic Flux Flux means “flow.” Magnetic flux is the “flow” of magnetic field lines through a closed path. 6 magnetic field lines pass through the loop. Maximum possible magnetic flux

4. Magnetic Flux Flux means “flow.” Magnetic flux is the “flow” of magnetic field lines through a closed path. 4 magnetic field lines pass through the loop so there’s less flux than when the loop was perpendicular to the magnetic field. The angle  is measured between the “normal” and the magnetic field.

5. Magnetic Flux Flux means “flow.” Magnetic flux is the “flow” of magnetic field lines through a closed path. 2 magnetic field lines pass through the loop so there’s less flux than before. The angle  is measured between the “normal” and the magnetic field.

6. Magnetic Flux Flux means “flow.” Magnetic flux is the “flow” of magnetic field lines through a closed path. 0 magnetic field lines pass through the loop so the flux is zero. so the magnetic flux is zero.

7. Another way to change magnetic flux Keep the orientation of the loop the same and change the magnetic field through the loop. (This is visualized by a change in the number of magnetic field lines that “flow” through the loop.) 2 magnetic field lines, thus there is less magnetic flux.

8. Another way to change magnetic flux Keep the orientation of the loop the same and change the magnetic field through the loop. (This is visualized by a change in the number of magnetic field lines that “flow” through the loop.) 4 magnetic field lines is more magnetic flux.

9. Another way to change magnetic flux Keep the orientation of the loop the same and change the magnetic field through the loop. (This is visualized by a change in the number of magnetic field lines that “flow” through the loop.) 6 magnetic field lines is more magnetic flux.

10. Pickup Coil A pickup coil refers to a coil that is in a magnetic field and is connected a resistor (or bulb). Ammeter can be used to measure current through the coil or a voltmeter can be used to measure the voltage across the resistor.

11. Faraday’s Lawelectromagnetic induction A changing magnetic flux through a coil will create an emf across the coil which creates a current through the coil. The emf is proportional to the rate of change of the magnetic flux. There are 3 ways to change the magnetic flux through the coil: Change the strength of the magnetic field at the plane of the coil. Change the angle (orientation) of the coil, with respect to the magnetic field. Change the area of the coil.

12. Generate an emf by changing the orientation of the coil Besides changing the orientation of the coil, one can instead leave the coil at rest and change the orientation of the magnetic field.

13. B b c a A circular loop of wire is again shown in three different positions as it rotates at constant angular speed in a uniform magnetic field. F is the magnetic flux (pictured as the number of magnetic field lines) crossing the loop. The rate DF/Dt at which Fis changing is greatest in magnitude when the loop passes ____________ and least when it passes ___________ . A. position a … position b B. position b … position a C. position c … position a or b

14. B b c a A circular loop of wire is again shown in three different positions as it rotates at constant angular speed in a uniform magnetic field. The instantaneous EMF induced in the loop is greatest in magnitude when the loop is passing ____________ and least when it is passing _____________ . • A. position a … position b • B. position b … position a • position c … position a or b

15. Generate an emf by changing the strength of the magnetic field 1. Move a magnet back and forth through the coil and the magnetic field at the plane of the loop “alternates” causing an alternating emf and alternating current.

16. N S N S 0 . - + 2 1 Situation a: The hand is stationary in position 1. Situation b: The hand is moving at moderate speed from position 1 to position 2. Situation c: The hand is moving quickly from position 1 to position 2. Situation d: The hand is stationary in position 2. 0 0 . . - + - + Which of the following correctly compares how far the galvanometer needle deflects during each of these situations? A. Most in d, least in a, same in-between value in b and c B. Most in d, less in c, still less in b, least in a C. Most in c, less in b, a and d tied for least D. Most in c, less in b, still less in d, least in a

17. Generate an emf by changing the strength of the magnetic field 2. OR use an electromagnet with an alternating current in the electromagnet. This creates an alternating magnetic field in the pickup coil which induces an alternating emf across the pickup coil.

18. + - 0 0 0 . . - + - + . - + By means of a sliding contact, we can change the amount of resistance that is included in the right hand circuit. Situation a: The contact is stationary in position 1. Situation b: The contact is slid at moderate speed from position 1 to position 2. 2 1 Situation c: The contact is slid quickly from position 1 to position 2. Situation d: The contact is stationary in position 2. 2. Which of the following correctly compares how far the galvanometer needle deflects during each of these situations? A. Most in d, least in a, same in-between value in b and c. B. Most in d, less in c, still less in b, least in a. C. Most in c, less in b, a and d tied for least. D. Most in c, less in b, still less in d, least in a.