Calculating the missing resistance when only given voltage

[jacob1995]

Homework Statement

I am asked to calculate the missing resistance(R5) when only given the voltage drop of of 14v across it

Homework Equations

current and divider rule
ohms law

The Attempt at a Solution

[/B]
i tried finding the current of the 6+10 ohm series resistor that is parallel to R5, which would mean they have the same voltage drop. Not sure where i would go from here since i don't know the total resistance, i can't find the total current that is being split between R5 and 6+10 resistor.

 

[nrqed]

Homework Statement

I am asked to calculate the missing resistance(R5) when only given the voltage drop of of 14v across it

Homework Equations

current and divider rule
ohms law

The Attempt at a Solution

[/B]
i tried finding the current of the 6+10 ohm series resistor that is parallel to R5, which would mean they have the same voltage drop. Not sure where i would go from here since i don't know the total resistance, i can't find the total current that is being split between R5 and 6+10 resistor.

Hello,

We would need the actual question with all the information provided to help you. Can you provide more details?

 

[jacob1995]

Hello,

We would need the actual question with all the information provided to help you. Can you provide more details?

whoops sorry, reuploaded the circuit

 

[nrqed]

whoops sorry, reuploaded the circuit

Ok, thank you.

As a first step, think of the resistors R3, R4 and R5 as a single equivalent resistance, let's call it Req. The voltage across this Req will be 14 volts too. Now, just from the information given, can you determine what must be the value of this Req?

 

[jacob1995]

Ok, thank you.

As a first step, think of the resistors R3, R4 and R5 as a single equivalent resistance, let's call it Req. The voltage across this Req will be 14 volts too. Now, just from the information given, can you determine what must be the value of this Req?

3 and 4 are in series, which is in parallel to R5? would i not require current to find the value of Req, since i am missing the value of R5

 

[nrqed]

3 and 4 are in series, which is in parallel to R5? would i not require current to find the value of Req, since i am missing the value of R5

What I suggest is to do the problem in two steps. As a first step, it is better to forget completely about R3, R4 and R5. Just call the combination of these three Req. Can you figure out the value of Req? Once you will know that, we will figure out R5.

 

[nrqed]

3 and 4 are in series, which is in parallel to R5? would i not require current to find the value of Req, since i am missing the value of R5

Hint: you know the potential of the battery (28 volts), you know the other resistors in the circuit an you know that there is 14 volts across Req. This is enough to find Req.

 

[jacob1995]

What I suggest is to do the problem in two steps. As a first step, it is better to forget completely about R3, R4 and R5. Just call the combination of these three Req. Can you figure out the value of Req? Once you will know that, we will figure out R5.

voltage divider rule?

 

[nrqed]

voltage divider rule?

Yes, that's one way to do it. Here the numbers given make the calculation very easy.

 

[jacob1995]

Yes, that's one way to do it. Here the numbers given make the calculation very easy.

so i got 14 = 28 x Req/ R(1+2+2)
= 2.5?

 

[nrqed]

so i got 14 = 28 x Req/ R(1+2+2)
= 2.5?

I am not sure what R(1+2+2) means.

The correct equation is $14 = \frac{28 R_{eq}}{1+2+2+R_{eq}}$

 

[jacob1995]

I am not sure what R(1+2+2) means.

The correct equation is $14 = \frac{28 R_{eq}}{1+2+2+R_{eq}}$

forgot to add Req back, got a vlaue of 10 for R5

 

[nrqed]

forgot to add Req back, got a vlaue of 10 for R5

Good job!

 

[jacob1995]

Good job!

thank you for the help