PHY303LHW9S

# The induced field through the coil in the circuit

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The induced field through the coil in the circuit with a resistor must produce a mag- netic field from left to right ( B induced = ) to resist any change of flux in the coil (Lenz’s law). The larger helical coil is wound clockwise (looking from left-hand end of the coil) from terminal a to terminal b . Using the right-hand rule, when the induced magnetic field is left to right ( B induced = ), the induced current through the resistor R flows from a through R to b ( I ). 019 10.0 points A magnetic dipole is falling in a conducting metallic tube. Consider the induced current in an imaginary current loop when the magnet is moving away from the upper loop and when the magnet is moving toward the lower loop. N S N pole I above dipole magnet v S pole I below ? ? y z x
rosen (arr956) – Homework 09 – Chiu – (58295) 11 Determine the directions of the induced currents I above and I below in an imaginary loop shown in the figure, as viewed from above, when the loop is above the falling magnet and when the loop is below the falling magnet. 1. I above = counter-clockwise and I below = clockwise correct 2. no current flow 3. I above = counter-clockwise and I below = counter-clockwise 4. I above = clockwise and I below = counter-clockwise 5. I above = clockwise and I below = clockwise Explanation: When the falling magnet is below the up- per loop, −→ μ ind must be up to attract the falling magnet and slow it down; i.e. , counter- clockwise as viewed from above. Before reaching the lower loop, −→ μ ind must be down to oppose the falling magnet; i.e. , clockwise as viewed from above. N S N pole I above dipole magnet v S pole I below y z x 020 10.0 points A pendulum consists of a supporting rod and a metal plate (see figure). The rod is piv- oted at O . The metal plate swings through a region of magnetic field (directed out of the paper). Consider the case where the pendu- lum’s metallic plate enters the magnetic field region from left to right. B B B B O e n t e ri n g fi e l d The direction of the induced magnetic field at the center of the circulating eddy current and the direction of the eddy currect are 1. into the plane and clockwise. correct 2. along the rod toward the pivot point and clockwise. 3. along the rod away from the pivot point and counter-clockwise. 4. along the direction of swing and counter- clockwise. 5. into the plane and counter-clockwise. 6. out of the plane and clockwise. 7. out of the plane and counter-clockwise. 8. along the direction of swing and clock- wise. 9. opposite to the direction of swing and counter-clockwise.
rosen (arr956) – Homework 09 – Chiu – (58295) 12 10. opposite to the direction of swing and clockwise. Explanation: A conduction electron in the pendulum will experience a magnetic force opposite the di- rection of vectorv × vector B , so using the right hand rule, we can determine that the motion of the electrons will be in the counter-clockwise di- rection, which produces a clockwise current.

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