Re: [Phys-l] About galvanometer in Wheatstone bridge

[Bernard Cleyet <bernardcleyet@redshift.com>]

http://www.lhup.edu/~dsimanek/scenario/labman4/wheats.htm





These questions are to be answered by doing a mathematical analysis  
of the bridge circuit, making use of circuit laws such as Kirchoff's  
laws and Thvenin's theorem. Do not appeal to your experimental data  
or results in answering these questions. (1) We hinted that the  
resistance of connecting wires could cause error, and suggested you  
use the shortest wires possible. In fact only some of the wires are  
critical. Which wires need to be short, and which don't matter?  
Explain why. Which can cause determinate errors, and which only  
affect the indeterminate errors? Why?

(2) What effect does the battery voltage have on the precision of the  
bridge? Would one with twice the voltage give twice the precision?  
(3) What effect does the galvanometer sensitivity have on the  
precision of the bridge? Would one twice as sensitive give twice the  
precision?

(4) What if the voltage of the power source you were using varied  
erratically, say by as much as 20%? What effect would this have on  
your experimental data and results, and how much?

(5*) Considering only the errors due to uncertainties in resistance  
of the bridge arms, show that the slidewire bridge is most precise  
when the slider is set at the center of the slidewire.

(6*) By changing the value of the resistance box R, the slidewire  
bridge may be made to balance at any desired point along the length  
of the slidewire AB. If it were balanced at a point 2 cm from one  
end, how would the accuracy of the measurement compare with a  
measurement of the same unknown resistor made with the balance point  
at the center of the wire?

Text and drawings © 1995, 2004 by Donald E. Simanek.



bc remembers the author as a (former?) member of this? list.

http://www.lhup.edu/~dsimanek/scenario/labman4/wheats.htm



http://en.wikipedia.org/wiki/Wheatstone_bridge

eq. given use diff. calculus.



p.s. I couldn't quickly find my lab. book from the 50's that I used  
so ...










On 2009, Nov 24, , at 07:04, CARABAJAL PEREZ, MARCIAL ROBERTO wrote:

> Hello:
>
> I am looking for a detailed discussion about the classical  
> combination Galvanometer- Wheatstone bridge, in particular the  
> sensitivity calculus in vicinity of the balance. Can you recommend  
> any paper/book ?.
> Thanks very much.
> Roberto
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