(adsbygoogle = window.adsbygoogle || []).push({}); [SOLVED] Circuits questions help(...supposedly they are easy.)

1. The problem statement, all variables and given/known data

Here is a picture of the question with the diagrams

http://img153.imageshack.us/img153/9741/questioniy3.jpg [Broken]

2. Relevant equations

Resistors in series/parallel,kirchoff's laws.

3. The attempt at a solution

For the part b) I just found the equivalent resistance and then used the fact that [itex]R_1=25R_2[/itex] and then found the total current using [itex]I=\frac{V}{R}[/itex]

and got:

[tex]I=(\frac{26}{26r+25R_2})*E[/tex]

so to find a desired value for I you would need to choose E,r and [itex]R_2[/itex] accordingly?

For part C) [This is where I think I did the question wrong]

p.d. through the voltmeter and [itex]60 \Omega[/itex] resistor =2V

So that the pd through the [itex]90 \Omega[/itex] resistor=6-2=4V

Current through the [itex]90 \Omega[/itex] resistor,I=[itex]\frac{4}{90}=.0444A[/itex]

Current through the [itex]60 \Omega[/itex] resistor,[itex]I_1[/itex]=[itex]\frac{2}{60}=0.033A[/itex]

By Kirchoff's first law:[itex]I=I_1 + I_2[/itex] ((I_2 is the current through the voltmeter))

so that [itex]I_2=I-I_1[/itex]

[tex]\frac{2}{R_v}=\frac{1}{90}[/tex]

and [itex]R_v=180 \Omega[/itex]

cii)

Total resistance=1038.46ohms

total current,I=6/1038.46=0.005777777~.0058A

pd through 900 ohm resistor=0.005777777*900=5.2V

pd through voltmeter and 600ohm resistor=6-5.2=0.8V

Not too sure what this says about voltmeters except that if they have resistance comparable to the other resistances they draw too much current and then some of the pd is lost in it.

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Circuits questions help( supposedly they are easy.)

**Physics Forums | Science Articles, Homework Help, Discussion**