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12th July 2018, 07:12 #1
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12th July 2018, 07:23 #2
Re: cant make sense of current, voltage, resistance relationship, graph
Hi,
You're not the only one. I feel like I'm walking into a trick question...
It looks like the relationship has been drawn upside down. I've yet to see a circuit where less resistance equals less current...

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12th July 2018, 07:37 #3
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Re: cant make sense of current, voltage, resistance relationship, graph
well thanks. It's not a trick. I can't make sense of it, and I guess it is wrong. But, what do i know? That is why I am asking. Is the graph upside down, or is it not possible to represent what its trying to represent with a single line?
   Updated   
what about these graphs. I think the first one makes sense, but not the second. correct?

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12th July 2018, 08:05 #4
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Re: cant make sense of current, voltage, resistance relationship, graph
I understand the relationship between V, I and R in written terms as in proportionality and the inverse. But I can't see how the graph relates. Can someone explain it please.

12th July 2018, 08:07 #5
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Re: cant make sense of current, voltage, resistance relationship, graph
Hi,
Post#1
I agree the graph doesn't make much sense.
There is Ohm's Law. R = V / I
And it says "constant voltage"
Let's calculate some values:
Let's assume V = 12V
Then: if
I = 1A > R = 12 Ohms
I = 2A > R = 6 Ohms
I = 4A > R = 3 Ohms
I = 6A > R = 2 Ohms
I = 12A > R = 1 Ohms
You see: the higher the current, the lower the resistance.
This is what the graph shows.
Mind: the graph has no X values and no Y values. In most cases the axis are linear > but there is no need for this.
Thus one may expect that the graph shows a hyperbola > but there is no need for this. With non linear axis the graph may look like a straight line.
Post#3:
Both graphs show the correct relationship:
Constant R: the higher the current, the higher the voltage
Constant current: The higher R, the giher V.
Both are directly proportional. In both casess: with both linear axis you will get a straight line graph.
I recommend to do some example calculations and graphs with Excel to get a feel.
KlausPlease donīt contact me via PM, because there is no time to respond to them. No friend requests. Thank you.
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12th July 2018, 08:19 #6
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12th July 2018, 08:42 #7
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Re: cant make sense of current, voltage, resistance relationship, graph
Hi,
You are correct with figure 1.21 and figure 1.23.
But you are not correct with figure 1.22.
See my example of post #5.
Mathematical solution:
V = constant, thus V1 = V2
V1 = R1 x I1
V2 = R2 x I2
because V1 = V2 we can say:
R1 x I1 = R2 x I2
Now we increase R2. Lets say R2 = 2 x R1
Then we get
R1 x I1 = 2 x R1 x I2 ; we divide both sides by R1
> I1 = 2 x I2
I2 = 1/2 x I1
we see that I2 is decreased.
This is named "indirect proportionality"
The higher R the lower I
Klaus
Added:
Chart with non linear "R" axis.
Please donīt contact me via PM, because there is no time to respond to them. No friend requests. Thank you.
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