Double-grounded circuit, find I across one of two resistors

[kamhogo]

Homework Statement

What is the current in the 2 ohms resistor?

Homework Equations

Kirchhoff's loop law

The Attempt at a Solution

Grounding does not affect how the circuit behaves, so I ignored the ground in and applied the loop law (clockwise from the negative terminal of the 9V battery ):

ΔV(loop) = 9V -(2 ohms)*I - 3V - (4 ohms)*I =0
6V = (6 ohms)*I
I = 1 A

Correct?

 

[drvrm]

Grounding does not affect how the circuit behaves, so I ignored the ground in and applied the loop law

well i do not work with circuits much- but if you have grounded both terminals of a load -can you expect a current to flow in the lower 4 ohms resistance.
grounding a circuit defines the potential to be zero (definitely)
further i failed to understand -what you wish to convey through this expt.?

 

[Orodruin]

Incorrect. The system is grounded at two different points, indicating that those points must have the same potential.

 

[epenguin]

^^...So you have the same simplification as in the last problem. After which...?

 

[kamhogo]

So I can ignore the 4 ohms resistor in my calculations? Then the current through the 2 ohms resistor would be given by:

9V - (2 ohms)*I - 3V =0
6V / 2 ohms = I = 3A

 

[kamhogo]

well i do not work with circuits much- but if you have grounded both terminals of a load -can you expect a current to flow in the lower 4 ohms resistance.
grounding a circuit defines the potential to be zero (definitely)
further i failed to understand -what you wish to convey through this expt.?

From what I understand now, the 4 ohms resistor might as well not be there...it's between 2 points of zero potential and so no current flows through it. Right?

 

[Orodruin]

From what I understand now, the 4 ohms resistor might as well not be there...it's between 2 points of zero potential and so no current flows through it. Right?

Right. You need a potential difference between its ends to provide a current.

In this respect, grounding the two points is like short-circuiting them.

 

[drvrm]

When connecting in Parallel you are doubling the capacity (amp hours) of the battery while maintaining the voltage of one of the individual batteries. Use a jumper wire between the positives of both batteries and another jumper wire between the negatives of both batteries. Connect your positive and negative wires to the same battery to run to your application.

 

[Orodruin]

When connecting in Parallel you are doubling the capacity (amp hours) of the battery while maintaining the voltage of one of the individual batteries. Use a jumper wire between the positives of both batteries and another jumper wire between the negatives of both batteries. Connect your positive and negative wires to the same battery to run to your application.

This does not add any insight to the current problem at hand. Please stay on topic.

 

[phyzguy]

So I can ignore the 4 ohms resistor in my calculations? Then the current through the 2 ohms resistor would be given by:

9V - (2 ohms)*I - 3V =0
6V / 2 ohms = I = 3A

This is correct.

 

[kamhogo]

When connecting in Parallel you are doubling the capacity (amp hours) of the battery while maintaining the voltage of one of the individual batteries. Use a jumper wire between the positives of both batteries and another jumper wire between the negatives of both batteries. Connect your positive and negative wires to the same battery to run to your application.

This is confusing...what's a jumper wire? Why connect the terminals?

 

[SammyS]

This is confusing...what's a jumper wire? Why connect the terminals?

Ignore the reply of @drvrm !

 

[CWatters]

When connecting in Parallel you are doubling the capacity (amp hours) of the battery while maintaining the voltage of one of the individual batteries. Use a jumper wire between the positives of both batteries and another jumper wire between the negatives of both batteries. Connect your positive and negative wires to the same battery to run to your application.

This is not relevant to this thread.

In addition it is wrong and potentially dangerous. In this thread the batteries are different voltages and batteries with different voltages should never be connected in parallel.

 

[kamhogo]

I'm getting better at this circuit analysis thing!

 

[SammyS]

View attachment 98526 I'm getting better at this circuit analysis thing!

etc.That seems correct.

The image is hard to read. I had to zoom way in.

In the future it's best to start a new tread for a new problem.

 

[epenguin]

View attachment 98530

View attachment 98532
etc.That seems correct.

The image is hard to read. I had to zoom way in.

In the future it's best to start a new tread for a new problem.

And to use an app like DocScanHD to make the images more visible and less unpleasant to look at.