# Finding error.

1. Oct 18, 2011

### athrun200

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

2. Relevant equations

3. The attempt at a solution
See photo2

I don't know why the error is lager than the area.
Is it possible?

#### Attached Files:

File size:
18.6 KB
Views:
50
• ###### 2.JPG
File size:
12.7 KB
Views:
50
2. Oct 18, 2011

### Liquidxlax

For each type of function there is a different error calculation

for lets say x = tsin(sy) the error would be

Δx = (Δy)tscos(sy) where t and s are some arbitrary constants

and something like

x = tzy were t is an arbitrary constant

then

(Δx/x)2 = (Δz/z)2 + (Δy/y)2 + 2(Δzy)2/zy

where 2(Δzy)2/zy is the covariance factor which i doubt you need to include.

so Δx = x√(all error added together and squared individually)

so

error calculations are a pain in the but in upper level physics studies but they are a necessity.

I'll give you an different example in case it doesn't make a lot of sense

Suppose that the area of a rectangle A=LW is to be determined from the following measurements of lengths of two sides:

L = 22.1 ± 0.1cm W= 7.3 ± 0.1cm

The relative contribution of ΔAL to the error in L will be

ΔAL/A = ΔL/L = 0.1/22.1 = 0.005

and the corresponding contribution of ΔAW will be

ΔAW/A = ΔW/W = 0.1/7.3 = 0.014

Thus ΔA will equal

ΔA = A√( 0.0142 + 0.0052)

ΔA = 0.015A

Last edited: Oct 18, 2011