- #1
ottjes
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Have some problems with thevenin (or my teacher is wrong, which i believe .
[PLAIN]http://www.fmf.nl/~wim/studie/cir1.png
example from my book:
Vi=15V, R1=6, R2=R3=3
Voc = Vi R2/(R1+R2) = 5 V (potential divider)
R2//R3=1.5 Ohm
R1+(R2//R3)=7.5 Ohm --> I = 15/7.5 = 2 A
Cause R2 and R3 are equal half of this current will flow to R2 and other half to R3 -->Isc = 1 (how will this change if R2 != R3?)
R = Voc/Isc = 5/1 = 5 Ohm
How i will solve this problem:
Leave R3 first out of the problem
Voc = Vi R2/(R1+R2) = 5 V
R1//R2 = (R1+R2)/(R1R2) = 9/16=2 Ohm
Now i have this:
http://www.fmf.nl/~wim/studie/cir2.png
R=(R1//R2)+R3=2+3=5 Ohm
This looks good, same as the book
On my test i got this question:
[PLAIN]http://www.fmf.nl/~wim/studie/cir1.png
With Vi=10 V and
R1=R2=R3=5 Ohm
Answer here must be, according to teacher: Voc=5V and R=3.75 Ohm
If i do this the same way as the book:
Voc = Vi R2/(R1+R2) = 5 V
R2//R3=2.5 Ohm
R1+(R2//R3)=7.5 Ohm --> I = 10/7.5 = 1.33 A
Cause R2 and R3 are equal half of this current will flow to R2 and other half to R3 -->Isc = 2/3 (how will this change if R2 != R3?)
R = Voc/Isc = 5/(2/3) = 7.5 Ohm (This is 2*3.75 :?)
Doing it my way:
Leave R3 first out of the problem
Voc = Vi R2/(R1+R2) = 5 V
R1//R2 = (R1+R2)/(R1R2) = 10/25=0.4 Ohm
R=(R1//R2)+R3=0.4+5=5.4 Ohm (different than the other answers :?)
What am i doing wrong, What is the good way to do this
edit: fixed url's
[PLAIN]http://www.fmf.nl/~wim/studie/cir1.png
example from my book:
Vi=15V, R1=6, R2=R3=3
Voc = Vi R2/(R1+R2) = 5 V (potential divider)
R2//R3=1.5 Ohm
R1+(R2//R3)=7.5 Ohm --> I = 15/7.5 = 2 A
Cause R2 and R3 are equal half of this current will flow to R2 and other half to R3 -->Isc = 1 (how will this change if R2 != R3?)
R = Voc/Isc = 5/1 = 5 Ohm
How i will solve this problem:
Leave R3 first out of the problem
Voc = Vi R2/(R1+R2) = 5 V
R1//R2 = (R1+R2)/(R1R2) = 9/16=2 Ohm
Now i have this:
http://www.fmf.nl/~wim/studie/cir2.png
R=(R1//R2)+R3=2+3=5 Ohm
This looks good, same as the book
On my test i got this question:
[PLAIN]http://www.fmf.nl/~wim/studie/cir1.png
With Vi=10 V and
R1=R2=R3=5 Ohm
Answer here must be, according to teacher: Voc=5V and R=3.75 Ohm
If i do this the same way as the book:
Voc = Vi R2/(R1+R2) = 5 V
R2//R3=2.5 Ohm
R1+(R2//R3)=7.5 Ohm --> I = 10/7.5 = 1.33 A
Cause R2 and R3 are equal half of this current will flow to R2 and other half to R3 -->Isc = 2/3 (how will this change if R2 != R3?)
R = Voc/Isc = 5/(2/3) = 7.5 Ohm (This is 2*3.75 :?)
Doing it my way:
Leave R3 first out of the problem
Voc = Vi R2/(R1+R2) = 5 V
R1//R2 = (R1+R2)/(R1R2) = 10/25=0.4 Ohm
R=(R1//R2)+R3=0.4+5=5.4 Ohm (different than the other answers :?)
What am i doing wrong, What is the good way to do this
edit: fixed url's
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