# short circuit current question..

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#### MrAl

##### Well-Known Member
Hi,

This is sort of simple but the drawing isnt that clearly drawn.
If the resistors are: 5,10,20,25 ohms, and the source is 9v and 1.8 amps,
then the person who did the original analysis did not do it correctly.
Isc is not equal to V2/10, it is equal to (V2-9)/10, which is 300ma.
They forgot to subtract the 9v from V2 before calculating the current.

Tell them to check their result.
It looks like you may need to check your result also.

The real problem however is that they use the notation "Isc" for both the
top and bottom loops, where the bottom loop is actually what they calculated:
1.5 amps
but the top loop is 0.3 amps.

So ask them which Isc they want to know. Apparently it is the bottom loop.

Last edited:

#### yusim

##### New Member
you state that between the green dot (9v) and red dot (V2) there is a 9v drop - if that was the case then V2 = 0 which would mean that there's no current through the 10Ω resistor which could not be the case because the current sources current has to go somewhere - so there is clearly not a 9v drop between the voltage source and V2

rather - figure out V2 the way its done in the handwriting under the circuit and then check the potetial difference between the voltage source and V2

#### transgalactic

##### Banned
Hi,

This is sort of simple but the drawing isnt that clearly drawn.
If the resistors are: 5,10,20,25 ohms, and the source is 9v and 1.8 amps,
then the person who did the original analysis did not do it correctly.
Isc is not equal to V2/10, it is equal to (V2-9)/10, which is 300ma.
They forgot to subtract the 9v from V2 before calculating the current.

Tell them to check their result.
It looks like you may need to check your result also.

The real problem however is that they use the notation "Isc" for both the
top and bottom loops, where the bottom loop is actually what they calculated:
1.5 amps
but the top loop is 0.3 amps.

So ask them which Isc they want to know. Apparently it is the bottom loop.

there is no 10 ohm resistor you can enlarge the foto
can you tell me what is not clear in the photo
so i could fix it up

#### yusim

##### New Member
there is no 10 ohm resistor
then whats the value of the horizontal resistor connected to the ground node? - according to the calculations under the circuit its value is 10Ω

can you tell me what is not clear in the photo
the value of the 10Ω resistor for one

#### transgalactic

##### Banned
oohhh sorry i just woke up
there is a 10 ohm ressistot

#### transgalactic

##### Banned
the top Isc is not related to this circuit
its Isc: (means we find now Isc)

i my way of solving is with the bigger letters

can you tell me whats wrong with it?

#### transgalactic

##### Banned
by the way the analisis is correct
there is no mistake
we have V2 drop on 10 ohm

#### MrAl

##### Well-Known Member
Hi again,

Ok then the 1.5 amp result is correct, as i already stated.

If you want us to find out why you make a mistake you have to show us
your work and perhaps why you did it that way. Im sure myself or someone
else would be happy to look your work over and see what went wrong, but
we have to see your work.

BTW it's better to just apply nodal or loop analysis to this problem rather than
try to figure out some shortcut. Shortcuts sometimes lead to errors, while
KVL and KCL wont.

Last edited:

#### transgalactic

##### Banned
i found the mistake
thanks

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