Based on the picture, how would I figure out the capacitance Cu when R1=3200 ohm, R2=10 kohms, and C1=0.5uF?

Question

radar · Answer

Please post the picture.

anonymous · Answer

http://www.enotes.com/jax/index.php/images?eventHandler=Question&uploadID=591&questionID=453429

radar · Answer

I don't see enough info, am I suppose to think the bridge is balanced is their some information provided for the value of c1.??

anonymous · Answer

Yes it's balanced

anonymous · Answer

isn't c1=0.5uF ?

anonymous · Answer

The answer I got is 0.16 uF

john_es · Answer

I was trying
$$R_1/Z(C_1,R_3)=R_2/C_u\Rightarrow C_u=R_2Z(C_1,R_3)/R_1$$With
$$Z(C_1,R_3)=|j\cdot1/(2πfC_1) + R_3|$$ But I haven't calculated the result.

anonymous · Answer

I'd feel better if you did ;-)

anonymous · Answer

my answer is based off of this formula...C1/R2xR1

john_es · Answer

The only problem I have using my formula is that I need the value of R_3, ¿Is it given in the problem?

anonymous · Answer

no

anonymous · Answer

Cu= C1/R2xR1 (the formula I used)

john_es · Answer

I think, if R_3=0, it should be, 
$$R_1/C_1=R_2/C_u\Rightarrow C_u=C_1R_2/R_1=1.56\ \mu F$$

jt950 · Answer

I have a questions guys,
can i use kirchoff's rule here?

anonymous · Answer

Ok i asked this question somewhere else and they got the same answer but.. in my book they gave me two example problems just like the problem i'm doing now, here's one of them...Based on the picture(picture I posted) R2=2000 ohm, and C1=0.002 uF. If the balance occurs when R1 is adjusted to 1700 ohms, what is the capacitence of Cu...they used the same formula I used and got 0.0017 uF

john_es · Answer

It is strange, but for references, I have used something like, http://electronicsproject.org/schering-bridge/ In any case, if you have doubts, better to follow the book ;). Also, Kirchoff's rules don't suit well in AC circuits.

radar · Answer

I may have lost a decimal point or two, but I get 1.6 uf.