Standard Deviation Problem in Physics. Help?

AI Thread Summary
The discussion revolves around calculating the uncertainty in the resistance (Rx) using a Wheatstone bridge setup, where L1 and L2 have specific lengths with associated uncertainties. The student is unsure about applying the division rule for uncertainties and is considering simply adding the uncertainties of +/- 0.05 cm from both measurements, resulting in a total uncertainty of +/- 0.10 cm. There is confusion regarding different methods of calculating deviations, particularly the propagation of errors, as the student has not been taught calculus-based approaches. The need for clear methods to determine deviations is emphasized, as varying techniques can yield significantly different results. The conversation highlights the importance of understanding uncertainty calculations in physics to avoid errors in subsequent problems.
cheechnchong
Messages
132
Reaction score
1
Standard Deviation Problem in Physics. Help!?

Homework Statement



In working with Wheatstone bridge one student chose the value for R1 so that the bridge is balanced at L1 = 48.5 cm and L2 = 51.2 cm. If Each measurement has an uncertainty of +/- .05, what would be the minimum value for the uncertainty in the calculation of Rx?

Given Equation: Rx = (L2/L1)*R1

The Attempt at a Solution



I know that R1 can be eliminated when looking at this question. However, my main concern is how to find the deviation using the Division rule? I have been exposed to several methods of finding the deviation. It confuses me a lot!

My guess is that, regardless of the sign (multiplication, division, subtraction, addition), the deviation +/- .10 . it's just a sum of the two .05 uncertainties in measurements.

I just need confirmation. I don't want to end up screwing up this problem...It's kind of a crucial step for the next few problems. Thanks for any help I can get!
 
Physics news on Phys.org
How does the formula for calculating the deviation in Rx look like?
 
Rx = (51.2 +/- 0.050 cm)/(48.5 +/- 0.050 cm)

im ignoring R1 because a random value was chosen for it. anyways, it just comes down to the uncertainties. how to solve it? I am thinking about adding them up, which would be 0.10 cm. what do you think?
 
I don't think this is correct. You said that you know of some methods to find the deviation. Do you know a method where you have to take partial derivatives?
 
Edgardo said:
I don't think this is correct. You said that you know of some methods to find the deviation. Do you know a method where you have to take partial derivatives?

nope, we never learned that. I'm taking the trig-algebra based physics. we will never learn anything that involves calculus. what is the other way?
 
Hmm...I thought it was about "Propagation of errors". Can you show some of the methods to determine the deviation?
 
Edgardo said:
Hmm...I thought it was about "Propagation of errors". Can you show some of the methods to determine the deviation?

it is, but I'm confused because there are many ways to do it. the many ways to do it often end up with different answers...i mean WAY different! that's why I am asking this board. it's cool. thanks for the help. i appreciate it!
 
Show at least one way how to calculate it and some other that yields a different result as you say.
 

Similar threads

Error Propogation for Half-Life
Replies
4
Views
3K
Uncertainty in the standard deviation
Replies
2
Views
12K
I Error propagation and standard deviation
Replies
3
Views
7K
Standard deviation change problem
Replies
24
Views
2K
How Do Standard Deviations Change with Multiple Measurements in Pendulum Timing?
Replies
1
Views
2K
How to ameliorate this Wheatstone bridge?
Replies
2
Views
2K
I Alternate expressions for the uncertainty propagation
Replies
1
Views
3K
A Low value standard deviation bias
Replies
6
Views
2K
Instrument Error or Standard Deviation
Replies
2
Views
3K
How to calculate standard deviation?
Replies
4
Views
2K

Hot Threads

Recent Insights

Back
Top