5.71 ohm.

One of the things you need to start practicing is asking if your answers (both final answers and intermediate answers) make sense.

Hopefully one thing that has been pointed out in your studies is that the equivalent resistance of two resistors in series is never smaller than either of the them while the equivalent resistance of two resistors in parallel is never larger than either of them.

So you know that the parallel resistance of a 5 Ω resistor and anything else is going to be no more than 5 Ω, hence you know that an answer of 5.71 Ω is wrong.

 

My mistake. It is 4ohm. But in the solutions the result is "5.82 ohm".

That is the answer for 8(a), which is Figure 12 in the document.

 

hi,
You are correct 4 Ohms.

So now to complete this circuit, post the individual equations for each step we have done, then end with a complete equation for the circuit, so that we can see that you understand the importance of the location of the brackets in the equations.

This is one of the points that WBahn was making

Do you follow that OK.

The others circuits are harder..

 

One of the things you need to start practicing is asking if your answers (both final answers and intermediate answers) make sense.

Hopefully one thing that has been pointed out in your studies is that the equivalent resistance of two resistors in series is never smaller than either of the them while the equivalent resistance of two resistors in parallel is never larger than either of them.

So you know that the parallel resistance of a 5 Ω resistor and anything else is going to be no more than 5 Ω, hence you know that an answer of 5.71 Ω is wrong.

Thats right. I confused the solutions. I am sorry. Thanks for the help.

 

Thats right. I confused the solutions. I am sorry. Thanks for the help.

So pick one that you are not getting the correct answer for and let's focus on it. SHOW YOUR WORK so that we can help you find what you are doing wrong and help you fix that hole in your understanding.

 

hi A,
Looks fine to me.
The other circuits maybe harder, but always look at a circuit to see if there are simple ways of reducing the layout, before writing equations.
In other words think about how you are going to solve it before writing equations.

Lets try another circuit, which do you choose.?
E

 

hi A,
Looks fine to me.
The other circuits maybe harder, but always look at a circuit to see if there are simple ways of reducing the layout, before writing equations.
In other words think about how you are going to solve it before writing equations.

Lets try another circuit, which do you choose.?
E

I choose this circuit. The 20ohm and the 5ohm resistances are in parallel, giving a 4ohm resistance. I think that the 18, 9 and 20 ohm are in parallel too(if so, it gives a 4.62 ohm resistance) but i am not sure. The simplier circuit is something like that?

 

hi,
You say
I choose this circuit. The 20ohm and the 5ohm resistances are in parallel, giving a 4ohm resistance.
Thats OK, but what about 1 Ohm in series.
That makes 5 Ohms in parallel with the 20 Ohm, so what is that value.??
E

 

Now we have something to work with.

You say that you think the 18 Ω, 9 Ω, and 20 Ω resistors are in parallel.

Why do you think that?

Remember that the definition of two two-terminal devices to be in parallel requires that they have the exact same voltage across them at all times.

Is that the case for all three of these resistors? Is it possible for the voltage across the 20 Ω resistor to be different than the voltage across the 9 Ω resistor? If so, they are not in parallel.

Hint: For the voltage across those two resistors to always be the same, what does the voltage across the 2 Ω always have to be? Is this reasonable?

 

Hi Bill,
I will sit this one out.
E

 

There are a couple of easy ways to see which components are in parallel and which aren't. Put your index fingers on opposite sides of a resistor. If you can move your fingers without picking them up and while staying on the same wires, such that they are on opposite sides of another resistor, then those two resistors are in parallel. If you can't, they aren't. Another useful trick is to color code all of the nodes using difference colors. Any two resistors that are connected to the same two colored nodes are in parallel, otherwise they aren't.

 

Hi Bill,
I will sit this one out.
E

No need to. Plus, I'm about to hit the sack and will be real busy most of tomorrow, so I'm gonna be pretty unresponsive for the next day or so.

 

hi,
So what do you calculate the equivalent resistance of the circuit.?
E

 

hi AD,
If you redraw the circuit as this image, it should make solving easier, try it, let us know the answer.?
E

 

hi AD,
If you redraw the circuit as this image, it should make solving easier, try it, let us know the answer.?
E

Hi. thank you both for your help so far. I apologize for not responding faster. simplifying the circuit makes it easier. I think the equivalent resistance would look like this: (it looks a bit confuse)

 

hi Antonio,
If you plug the resistance values into that equation what do you make the equivalent resistance.?
E

Update:

Let Ra= ((R2||R3)+R4)) === ?

Let Rb = (Ra || R8)+ R7 === ?

Let Rc = (R5 || R6) == ?

Plugging in the values what you make Ra , Rb & Rc ../

Note at thsi stage you could redraw the network for Ra,Rb, Rc and R1

E

 

Hi. thank you both for your help so far. I apologize for not responding faster. simplifying the circuit makes it easier. I think the equivalent resistance would look like this: (it looks a bit confuse)
View attachment 221251

Doesn't look right to me. It seems that you have the brackets in the wrong places.

For example, what is R1 in series with?
What is R8 in parallel with?

 

hi Antonio,
If you plug the resistance values into that equation what do you make the equivalent resistance.?
E

Update:

Let Ra= ((R2||R3)+R4)) === ?

Let Rb = (Ra || R8)+ R7 === ?

Let Rc = (R5 || R6) == ?

Plugging in the values what you make Ra , Rb & Rc ../

Note at thsi stage you could redraw the network for Ra,Rb, Rc and R1

E

Ra = 5 ohm
Rb = 6 ohm
Rc = 6 ohm
But my equation is correct?

 

Doesn't look right to me. It seems that you have the brackets in the wrong places.

For example, what is R1 in series with?
What is R8 in parallel with?

How would you write it?

 

hi,
Try breaking down the same way as we did the first problem.
Redraw the circuit with the known values you have calculated.
E