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Author Topic: Electronics quiz  (Read 3851 times)

TokMor

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Electronics quiz
« Reply #10 on: August 24, 2003, 12:36:38 AM »

you are correct, and you get the point.

What is the time constant for this circuit?
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Infindense

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Electronics quiz
« Reply #11 on: August 24, 2003, 06:14:29 AM »

An RC time constant relating the time required to charge (or discharge) a capacitor exists.  To completely change from one voltage level to a new level of source voltage, the capacitor needs 5 RC time constants.  One RC time constant (t) = R (in Ohm's) x C (in farads).
t = R  x C
so
t = 1000 Ohm's x 0.001 Farads
t = 1

I think.
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Daneel

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Electronics quiz
« Reply #12 on: August 24, 2003, 09:18:39 AM »

sorry, can't really provide a reason, but in my quest for an answer, i turned up this site:

RC Circuit Simulator

EDIT - i get ~5 seconds as my answer (amount of voltage left should be about 1%)
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TokMor

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Electronics quiz
« Reply #13 on: August 24, 2003, 04:29:12 PM »

Infindense: you are close, you have the right answer, but with the wrong reasoning. I'll give you the point anyway though. For the formula you used, you are supposed to take the inverse of R*C, but in this case that gives you the same number.

Assumeing the capacitor starts uncharged, what will the voltage across the capacitor be as a function of time?
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Infindense

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Electronics quiz
« Reply #14 on: August 24, 2003, 05:19:00 PM »

This stuff is confusing.  Now I know why I slept through that class.
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TokMor

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Electronics quiz
« Reply #15 on: August 27, 2003, 09:17:31 AM »

yeah, I don't know what I was thinking with that question, I'll bring it back to something more computer related.

I have 5V power from a molex connecter splice and a motor rated at 3V and 50mA. I also have a DPDT switch and a variable resistor. How should I wire up the motor so that I can change the direction of it by flipping the switch, and what should I set the resistor to to keep from burning the motor out?
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viridius

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Electronics quiz
« Reply #16 on: August 28, 2003, 05:55:12 PM »

40 ohms ((5-3)/0.05).  Connect the resistor to one of the leads from the power supply.  Connect the motor to the common leads of the switch and then connect the power to the remaining position pairs, alternating positive and negative.  Question: I have a slide switch that has 8 pins arranged in two colunms of four.  The switch has three positions.  In each position, a pin in a column is connected to the pin next to it so if the switch looks like:
Aa
Bb
Cc
Dc
In position one, AB and ab are connected; in position two, BC and bc are connected, and in position three; CD and cd are connected.  How can you connect two motors so that in one position both motors are on, in another, only one motor is on, and in yet another position, the other motor is on.
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Brain

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Electronics quiz
« Reply #17 on: August 29, 2003, 04:17:27 PM »

this thread kicks ass. although totally confusing in some parts, totally helpful in other parts. keep it up!
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