Penn Electronics Course PHYS 564

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Penn Electronics Course PHYS 564

Post by Admin on Fri Sep 01, 2017 10:36 am

I had my first class yesterday, it is going to one hell of a semester, and it was quite enlightening. We had setup a voltage divider system with a 1/2 resistor ratio. The voltage divider factor was 2/3. We attached a resistor load and started varying the resistance(potentiometer) from 0 to 10kOhms finding a linear relationship between voltage and current with a slope of -0.65 kOhms. We were asked about the significance of this slope, which puzzled me. This number appears two times, other than the current occurrence; The voltage divider ratio(very close), and the Thevenin Equivalent Resistance. I believe the slope is closely related to the Thevenin Equivalent Resistance. A followup experiment could have been using the the other resistor as the voltage divider. Would we still obtain a slope of -0.65 or would it change. This experiment will check to see if the slope is intrinsic to the voltage divider system or not.


I could perform this experiment at Bryn Mawr, I believe I have access to all the equipment in Bryn Mawr.

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September 15th

Post by Admin on Fri Sep 15, 2017 1:55 pm

Great, I want to cover or review what I have learned in the Electronics lab:

First voltage dividers are great and easy to understand. In application, they only work if the input impedance is large compared to the voltages of the voltage divider, if not then the measure voltage will not come out as expected.

The reason for this has to do with current flow/energy flow. Ideally you want all of the energy flowing through the voltage divider and none through the load. However, this is only true if the load resistance is much larger than the Volt. divider's resistances; due to the tendency of current to flow through the least resistance.

This week we have been looking at transients and AC circuits, the main focus begin RC-circuits. Essentially in both cases the voltage across the circuit elements are varying with time.
In the transients, we studied low/high-pass filters and found that the resistor acts like a high-pass filter, and the capacitor acts like a low-pass filter. (this is true in AC circuits as well)
The reason they act this way has to do with how the resistor and capacitor obtain a voltage. The resistor is dependent on the current while the capacitor is dependent on the charge. At high-frequency(with AC-circuits in mind, but it is the same in transients) the capacitor has little time to charge, meaning it will not hinder current flow. This implies that the capacitor acts like a short in the high-frequency regime. At low-frequencies the capacitor has enough time to charge meaning it will hinder current flow.
Another interesting comment about RC-circuits is that they act as an integrator and differentiator.

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