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phy124:lab_4 [2010/02/10 21:44]
mdawber
phy124:lab_4 [2010/02/19 12:33] (current)
mdawber
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====== PHY 124 Lab 4 - Magnetic Force and Induction ====== ====== PHY 124 Lab 4 - Magnetic Force and Induction ======

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The purpose of this laboratory is in Part I to observe the magnetic force on moving electrons due to the magnetic field from a bar magnet. The purpose of Part II is to observe the induction of a voltage in a coil by the change of the magnetic flux through the coil. In Part III the voltage induced in a coil by an alternating current (AC) from a second coil is observed. These two coils are arranged similar to a transformer. The purpose of this laboratory is in Part I to observe the magnetic force on moving electrons due to the magnetic field from a bar magnet. The purpose of Part II is to observe the induction of a voltage in a coil by the change of the magnetic flux through the coil. In Part III the voltage induced in a coil by an alternating current (AC) from a second coil is observed. These two coils are arranged similar to a transformer.
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+===== Video =====
+<​flashplayer width=640 height=480>​file=http://​www.ic.sunysb.edu/​Class/​phy122ps/​labs/​phy122vid/​lab4vidhq.flv</​flashplayer>​

===== Equipment ===== ===== Equipment =====
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**Note:** Here the magnetic field which contributes dominantly to the magnetic flux inside the coil is the magnetic field inside the magnet, indicated by the high density of field lines at either end of the bar. The average magnetic field is directed parallel to the axis of the bar and goes straight from the south to the north pole inside the bar.  This is the direction of the magnetic field you are concerned about for this part of the lab.  You are no longer interested in the field outside of the magnet like you were in Part I.  (see the sketch for Part I above) **Note:** Here the magnetic field which contributes dominantly to the magnetic flux inside the coil is the magnetic field inside the magnet, indicated by the high density of field lines at either end of the bar. The average magnetic field is directed parallel to the axis of the bar and goes straight from the south to the north pole inside the bar.  This is the direction of the magnetic field you are concerned about for this part of the lab.  You are no longer interested in the field outside of the magnet like you were in Part I.  (see the sketch for Part I above)

-Insert the bar magnet north pole first from left to right, slowly into the coil and observe the needle deflection. Note whether the needle deflection stays at maximum or falls back to zero when the magnet motion ceases. Then withdraw the magnet slowly from the coil and observe the needle deflection. Note the direction of the needle deflection. Do it a couple of times.+Insert the bar magnet ​**north pole first from left to right**, slowly into the coil and observe the needle deflection. Note whether the needle deflection stays at maximum or falls back to zero when the magnet motion ceases. Then withdraw the magnet slowly from the coil and observe the needle deflection. Note the direction of the needle deflection. Do it a couple of times.

Repeat this procedure with a fast motion of the bar magnet. Repeat this procedure with a fast motion of the bar magnet.
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BE CAREFUL! ​ When observing the signals from Channel 1 and Channel 2 remember that the signal for each channel has its own VOLT/DIV setting. ​ Take this into account when labeling your sketch and when computing the amplitude of each wave. BE CAREFUL! ​ When observing the signals from Channel 1 and Channel 2 remember that the signal for each channel has its own VOLT/DIV setting. ​ Take this into account when labeling your sketch and when computing the amplitude of each wave.

-From the ratios of the voltages you can calculate the ratio of the number of turns in the two coils. ($\large \frac{V_{2}}{V_{1}}=\frac{N_{2}}{N_{1}}$ See Ch 19 Sheet 24) +From the ratios of the voltages you can calculate the ratio of the number of turns in the two coils. ($\Large \frac{V_{2}}{V_{1}}=\frac{N_{2}}{N_{1}}$ See Ch 19 Sheet 24)

Are the frequencies of the two waves the same? Discuss with your TA whether they are or aren't and whether you observation is consistent with your expectation. Are the frequencies of the two waves the same? Discuss with your TA whether they are or aren't and whether you observation is consistent with your expectation. 