Circuit Lab B/C

Test your knowledge of various Science Olympiad events.
UTF-8 U+6211 U+662F
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Re: Circuit Lab B/C

Postby UTF-8 U+6211 U+662F » September 23rd, 2018, 9:13 am

Jacobi wrote:
UTF-8 U+6211 U+662F wrote:All right!

Describe the behavior of an RC circuit which is a) charging and b) discharging.


Answer
a) The voltage through the resistor starts high and decays exponentially as the capacitor becomes saturated. The charged capacitor has an extremely high voltage drop.
b) The voltage through the resistor starts high and decays exponentially as the capacitor discharges. The capacitor acts as a voltage source in the absence of other sources.

Yep, your turn.

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Re: Circuit Lab B/C

Postby Jacobi » September 26th, 2018, 2:53 pm

Do current and voltage sources exist in real circuits?

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Re: Circuit Lab B/C

Postby UTF-8 U+6211 U+662F » September 26th, 2018, 3:34 pm

Jacobi wrote:Do current and voltage sources exist in real circuits?

Answer
Not ideal ones but they can be approximated; however, real-life sources have a limited amount of charge (which can be measured in ampere-hours) and have internal resistance that sometimes needs to be accounted for.

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Re: Circuit Lab B/C

Postby Jacobi » September 26th, 2018, 4:47 pm

UTF-8 U+6211 U+662F wrote:
Jacobi wrote:Do current and voltage sources exist in real circuits?

Answer
Not ideal ones but they can be approximated; however, real-life sources have a limited amount of charge (which can be measured in ampere-hours) and have internal resistance that sometimes needs to be accounted for.

Right! Your turn.

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Re: Circuit Lab B/C

Postby UTF-8 U+6211 U+662F » September 26th, 2018, 4:55 pm

What is doping in the context of PN junctions and why is it done?

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Re: Circuit Lab B/C

Postby mdv2o5 » September 26th, 2018, 8:13 pm

UTF-8 U+6211 U+662F wrote:What is doping in the context of PN junctions and why is it done?


Answer
Pure silicon has four valence electrons that are able to conduct electricity. Doping adjusts the concentrations of the charge carriers within the silicon crystals to either increase the number of electrons or increase the number of "holes" (aka lack of electrons). Doping with elements that have 5 valence electrons such as arsenic increases the number of electrons in the silicon crystal. This makes it "negative" or n-type. Doping with elements that have 3 valence electrons such as boron or indium creates silicon crystals that have a high concentration of holes, making it "positive" or p-type. This causes electrons to move only in one direction: from n-type to p-type. This is essentially a silicon diode. The property of allowing electrons to only flow in one direction forms the basis for more advanced transistors such as BJTs and MOSFETs.

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Re: Circuit Lab B/C

Postby UTF-8 U+6211 U+662F » September 27th, 2018, 1:19 pm

mdv2o5 wrote:
UTF-8 U+6211 U+662F wrote:What is doping in the context of PN junctions and why is it done?


Answer
Pure silicon has four valence electrons that are able to conduct electricity. Doping adjusts the concentrations of the charge carriers within the silicon crystals to either increase the number of electrons or increase the number of "holes" (aka lack of electrons). Doping with elements that have 5 valence electrons such as arsenic increases the number of electrons in the silicon crystal. This makes it "negative" or n-type. Doping with elements that have 3 valence electrons such as boron or indium creates silicon crystals that have a high concentration of holes, making it "positive" or p-type. This causes electrons to move only in one direction: from n-type to p-type. This is essentially a silicon diode. The property of allowing electrons to only flow in one direction forms the basis for more advanced transistors such as BJTs and MOSFETs.

Yep, your turn!

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Re: Circuit Lab B/C

Postby mdv2o5 » September 27th, 2018, 2:13 pm

Calculate the RMS voltage of a 12V peak-to-peak sinusoidal AC signal and a 0-6V square wave with a time-on of 8ms and a period of 10 ms.

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Re: Circuit Lab B/C

Postby UTF-8 U+6211 U+662F » September 27th, 2018, 3:31 pm

mdv2o5 wrote:Calculate the RMS voltage of a 12V peak-to-peak sinusoidal AC signal and a 0-6V square wave with a time-on of 8ms and a period of 10 ms.

Answer



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Re: Circuit Lab B/C

Postby mdv2o5 » September 27th, 2018, 7:45 pm

UTF-8 U+6211 U+662F wrote:
mdv2o5 wrote:Calculate the RMS voltage of a 12V peak-to-peak sinusoidal AC signal and a 0-6V square wave with a time-on of 8ms and a period of 10 ms.

Answer




Looks good!

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Re: Circuit Lab B/C

Postby UTF-8 U+6211 U+662F » September 28th, 2018, 9:00 am

All right! Derive an equation for the power given off by a resistor from Ohm's law.

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Re: Circuit Lab B/C

Postby Jacobi » September 28th, 2018, 1:56 pm

UTF-8 U+6211 U+662F wrote:All right! Derive an equation for the power given off by a resistor from Ohm's law.


My Answer
By Ohm's law, . By the definition of power, . Thus, .

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Re: Circuit Lab B/C

Postby UTF-8 U+6211 U+662F » September 28th, 2018, 2:01 pm

Jacobi wrote:
UTF-8 U+6211 U+662F wrote:All right! Derive an equation for the power given off by a resistor from Ohm's law.


My Answer
By Ohm's law, . By the definition of power, . Thus, .

Yep, your turn, although I was thinking of a derivation using
Definition

But that's a little more complicated (and equivalent).

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Re: Circuit Lab B/C

Postby Jacobi » October 4th, 2018, 1:29 pm

Two resistors are combined in a circuit. First, they are combined in series. Then, they are combined in parallel. What is the equivalent single resistance of each setup?

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Re: Circuit Lab B/C

Postby UTF-8 U+6211 U+662F » October 4th, 2018, 1:32 pm

Jacobi wrote:Two resistors are combined in a circuit. First, they are combined in series. Then, they are combined in parallel. What is the equivalent single resistance of each setup?

Answer



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