What's the current from this circuit? Is it a short circuit or not?

In summary, a short circuit is a direct and unintended connection in an electrical circuit that can result in increased current flow and potential damage or fire hazards. To determine if a circuit has a short circuit, a multimeter can be used. The most common causes of a short circuit include damaged wiring, loose connections, faulty components, and environmental factors. Short circuits can be dangerous and should be addressed and fixed to ensure safety. To prevent short circuits, regular maintenance and proper use of fuses and circuit breakers are important.
  • #1
Helly123
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Homework Statement


Pic A, what's the I2?
kevnnb.png

Pic B, what's the current across a-b ?
15fllk1.png

Homework Equations



V = I*R
Voltage in series is different, the current is the same
Current in parallel is different, the voltage is the same

The Attempt at a Solution


from Pic A, I found that I1 = 1A, I3 = 1A, and V of 4ohm is 4V, V of 8ohm = 8V
it seems that 8V and I2 don't across 8ohm resistor. why?

from Pic B, I think that the current across a-b is 0A, since it's short-circuit. It's short circuit because the amount of V across 4 ohm + 1ohm the same as which across 8ohm + 2ohm. Is it right?
 

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  • #2
Your answers are correct, but your relevant equations don't seem to help you. You could study the Kirchoff laws and see if you can find useful relationships to get a complete set of equations.

For B, your argument 'since it's short circuit' doesn't hold. It's also short-circuit if one of the resistors is missing -- and in such a case there is a current flowing.

(I think you don't actually mean 'short-circuit' ...)
 
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  • #3
Helly123 said:
from Pic A, I found that I1 = 1A, I3 = 1A, and V of 4ohm is 4V, V of 8ohm = 8V
it seems that 8V and I2 don't across 8ohm resistor. why?
Since you know I1 and I3, you should be able to find I2 using KCL. What is your question here exactly?
Helly123 said:
from Pic B, I think that the current across a-b is 0A, since it's short-circuit. It's short circuit because the amount of V across 4 ohm + 1ohm the same as which across 8ohm + 2ohm. Is it right?
As BvU pointed out, that's not the reason why Iab=0. Look up 'balanced Wheatstone bridge'.
 
  • #4
BvU said:
Your answers are correct, but your relevant equations don't seem to help you. You could study the Kirchoff laws and see if you can find useful relationships to get a complete set of equations.

For B, your argument 'since it's short circuit' doesn't hold. It's also short-circuit if one of the resistors is missing -- and in such a case there is a current flowing.

(I think you don't actually mean 'short-circuit' ...)
I see.. if there's current, I3 = I1 + I2
I2 = 0A
Why?
 
  • #5
Helly123 said:
I see.. if there's current, I3 = I1 + I2
I2 = 0A
Why?
Because KCL tells you so.
The 8V voltage source is redundant here. You can remove it and still get the same voltages and currents everywhere in the circuit.
 
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  • #6
BvU said:
For B, your argument 'since it's short circuit' doesn't hold. It's also short-circuit if one of the resistors is missing --
If 4ohm missing, the voltage drop in a-b isn't zero. So, why it's still short circuit ?
I forgot to mention that resistor in wire a-b is 0,002 ohm.
What's short circuit? When the current is 0A?

and in such a case there is a current flowing.
there is a current flowing... so it's not 0A
 
  • #7
cnh1995 said:
Because KCL tells you so.
The 8V voltage source is redundant here. You can remove it and still get the same voltages and currents everywhere in the circuit.

But on the right side, Loop 2. The resistor is 8ohm? The I2 = 8V/8ohm = 1A (this doesn't apply?)
 
  • #8
Helly123 said:
there is a current flowing... so it's not 0A
No, I2 is zero as given by KCL.
Helly123 said:
But on the right side, Loop 2. The resistor is 8ohm? The I2 = 8V/8ohm = 1A (this doesn't apply?)
It does, but the expression gives I3 and not I2. To find I2, you can use only KCL.
 
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  • #9
Helly123 said:
If 4ohm missing, the voltage drop in a-b isn't zero. So, why it's still short circuit ?
I forgot to mention that resistor in wire a-b is 0,002 ohm.
What's short circuit? When the current is 0A?
The solution has nothing to do with the concept of open circuit or short circuit.
If you consider the circuit as it is (without any resistor 'missing'), do you agree that Iab=0A?
(It's actually simpler to explain why, now that you've mentioned Rab=0.002 ohm.)
 
  • #10
cnh1995 said:
The solution has nothing to do with the concept of open circuit or short circuit.
If you consider the circuit as it is (without any resistor 'missing'), do you agree that Iab=0A?
(It's actually simpler to explain why, now that you've mentioned Rab=0.002 ohm.)
I agree, but is it right?
Beside, if there's is a missing resistor before a-b make the circuit unbalanced, and the current a-b definitely not zero.
 
  • #11
Helly123 said:
I agree, but is it right?
Beside, if there's is a missing resistor before a-b make the circuit unbalanced, and the current a-b definitely not zero.
Yes to both.
 
  • #12
Helly123 said:
What's short circuit? When the current is 0A?
No. When the voltage difference is 0 V for nonzero current, no matter what the current. In other words: when the resistance is zero.
 
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Related to What's the current from this circuit? Is it a short circuit or not?

1. What is the definition of a short circuit?

A short circuit occurs when there is a direct and unintended connection between two points in an electrical circuit, bypassing the intended load. This results in a sudden increase in current flow, potentially causing damage to the circuit or creating a fire hazard.

2. How can I determine if a circuit has a short circuit?

To determine if a circuit has a short circuit, you can use a multimeter to measure the current flow in the circuit. If the current is significantly higher than the expected value, it is likely that there is a short circuit present.

3. What are the common causes of a short circuit?

The most common causes of a short circuit include damaged or faulty wiring, loose connections, and faulty components such as fuses or circuit breakers. Environmental factors such as moisture or debris can also cause short circuits.

4. Can a short circuit be dangerous?

Yes, a short circuit can be dangerous as it can cause overheating, sparks, and potentially lead to electrical fires. It is important to address and fix any short circuits in order to ensure the safety of yourself and others.

5. How can I prevent a short circuit from occurring?

To prevent a short circuit, it is important to regularly check and maintain your electrical wiring and components. Avoid overloading circuits and make sure all connections are secure. It is also important to use the correct fuses and circuit breakers for your electrical system.

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