# Quiz Help

Discussion in 'Homework Help' started by BirdMan, Oct 9, 2010.

1. ### BirdMan Thread Starter New Member

Oct 9, 2010
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New here but I will defintely stick around. This site has already been very helpful and the people seam real nice.

Bit about me:

Im 25 and in my first semester of a associated degree majoring to be a electrical technician within the energy systems sector.

For some reason I am second guessing my answer to this problem. Is the answer simply VT which I figured out to be 46.78v?

The given problem was in black and my answers are in red.

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2. ### bertus Administrator

Apr 5, 2008
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3. ### BirdMan Thread Starter New Member

Oct 9, 2010
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I am very aware of the characteristics of series and parallel circuits. Well kinda... lol

I figured IT by finding RT and VT.

Im not sure if this is just a weird electronic coincidence but adding up all the current from all three resistors and dividing by three gave me a number real close to my IT.

4. ### bertus Administrator

Apr 5, 2008
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Hello,

So you know Ohms law.
Then you can calculate the voltage across each resistor using the values of them and the total current.

Bertus

5. ### Markd77 Senior Member

Sep 7, 2009
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You've got the right current and voltage for R3, but you need to use that current to calculate the other 2 voltages.

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6. ### BirdMan Thread Starter New Member

Oct 9, 2010
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I done that also with R1 being 18.2v R2 16.7v R3 11.8.

It equals 46.7v.

My question is: What is the highest voltage I can have with out burning up resistors? Is it the total voltage or is there a amount you can go over Vt?

EDIT:

Markd77 just made me have a bright light go off in my head. Since that is the smallest resistor I need to use that current amount because if i use any higher current in series it will blow that resistor? Am I right?

7. ### Markd77 Senior Member

Sep 7, 2009
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I get about 14V for R1 with 27.5mA.
As this is theoretical assume the resistors burn at their power ratings. In real life the power rating is more complicated but it's usually best to stay well below because they do get pretty hot at full rated power.

8. ### BirdMan Thread Starter New Member

Oct 9, 2010
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Thanks for the help. Great site and great help.

9. ### Markd77 Senior Member

Sep 7, 2009
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594
If you've got about 36V for the answer then all is good.

Apr 5, 2008
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11. ### Georacer Moderator

Nov 25, 2009
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If I were in your place I would try this method: You know that all the resistors share the same current (and should be as they are connected in series). You also know that the formula for power is $P=I^2 \cdot R$. So, I would use it for each resistor to find the maximum current that can pass through it. Then I would take the smallest of them, as it prevents all the resistors from burning up.

Choosing that current, use the Ohm's law to calculate the voltage on each resistor, and sum them to find the voltage on the voltage source.