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Phy 202
Your 'question form' report has been received. Scroll down through the document to see any comments I might have inserted, and my final comment at the end.
** Question Form_labelMessages **
substitute_E_and_M_lab(s)
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As I mentioned in my submission of the first half of the honors version of the optics lab, I'd like to get the alternative E&M lab(s) done this weekend or early this coming week.
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What I do understand about the situation:
- I'm looking forward to this lab.
What I do not understand about the situation:
- What specific tasks you'd like me to perform
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While I'm working on the convex-lenses part of the honors version of the optics lab, would you please send me the alternative E&M lab(s) so that I can get started on and, I hope, finish it/them this weekend?
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Here's a start:
Using the generator, the leads to a good conductor (e.g., a coin or whatever) and crank it. Then connect it to a poor conductor (e.g., a piece of wood) and crank it.
How does the mechanical resistance you feel in the crank relate to the flow of current? In terms of energy, why does this make sense?
Now attach to light the three bulbs (easiest with bulbs in holder and clips on the tabs). Light each just barely. Which bulb requires the greatest and which the least cranking rate? Which requires the most and which the least force? Can you determine which bulb requires the most and which the least power to barely light?
Note that the voltage and current ratings are marked on the metal base of each bulb. Do your results appear to be consistent with these ratings? Note that you aren't lighting the bulbs fully, not using the rated voltage, so there isn't necessarily a correlation here. But there might be.
Now pick the bulb that required the most, and the bulb that required the least force. Connect them in series and crank so that only one lights, and that just barely. Either reverse the clips or reverse the cranking direction and see if this makes any clear difference in which bulb lights and in the speed or force of the cranking. Observe and record the cranking rate.
Crank so that both bulbs light, one just barely. Observe the required cranking rate and also compare the mechanical resistance you encounter. The mechanical resistance is difficult to separate out from cranking rate, but do your best.
Repeat with the bulbs in parallel, again cranking so that only one bulb lights. Is it the same bulb as before? Do you have to crank more quickly or more slowly? Is the mechanical resistance greater or less than with the series combination?
Now crank so that both bulbs light, one just barely and make the usual comparisons, as best you can.
Remembering that relative force is difficult to judge when cranking rates differ, give your best thinking on whether the series or the parallel circuit required more power when one bulb was barely lit.
Make the same comparison, or give your best thinking, for the case it which both bulbs lit.
OK, now you can use a meter. Analog is much better since the voltage produced by the generator is very jumpy.
Using the same bulb as before, attach the generator in series with the ammeter and the bulb, with the ammeter on a scale of about 150 - 250 milliamps. Is there a difference in the cranking rate necessary to barely light the bulb? Can you perceive a difference in the force required with and without the ammeter? Note also the current.
If the current is low enough, repeat with a lower scale (say, a 50 milliamp scale, but only if the current read on the higher scale was less than the maximum range of the scale).
Now change the meter to a voltage setting (typical scale might be around 10 or 20 volts) and put it in series with the bulb. Try to light the bulb, but don't get overzealous with the generator because you aren't going to be able to light it. However the meter will very likely read something. Can you explain what's going on here?
Now connect the meter in parallel with the bulb and try again. What happens?
OK, now use the ammeter and voltmeter settings to investigate the series and parallel circuit and see what you can discover. When you're using the ammeter setting, start your cranking very slowly so you don't accidentally blow the fuse, as you will tend to do if you attach the ammeter in parallel rather than in series. You can also assure yourself that you're cranking in the right direction.
More later, but one quick bit of foreshadowing: The resistance of the filament in a bulb changes with its temperature, which in turn varies with current. Taking readings of voltage and current you can determine the resistance of the bulb. Can you come up with data showing the dependence of bulb resistance on current?
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