Propagation Of Error Lnx
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constant size. Indeterminate errors have unpredictable size and sign, with equal likelihood of being + or -. RULES FOR ELEMENTARY OPERATIONS (DETERMINATE ERRORS) SUM RULE: When R = A + B then ΔR = ΔA + ΔB DIFFERENCE RULE: When error propagation natural log R = A - B then ΔR = ΔA - ΔB PRODUCT RULE: When logarithmic error calculation R = AB then (ΔR)/R = (ΔA)/A + (ΔB)/B QUOTIENT RULE: When R = A/B then (ΔR)/R = (ΔA)/A + (ΔB)/B POWER RULE:
Log Uncertainty
When R = An then (ΔR)/R = n(ΔA)/A or (ΔR) = n An-1(ΔA) Memory clues: When quantities are added (or subtracted) their absolute errors add (or subtract). But when quantities are multiplied (or divided), their relative
Logarithmic Error Bars
fractional errors add (or subtract). These rules will be freely used, when appropriate. We can also collect and tabulate the results for commonly used elementary functions. Note: Where Δt appears, it must be expressed in radians. RULES FOR ELEMENTARY FUNCTIONS (DETERMINATE ERRORS) EQUATION ERROR EQUATION R = sin q ΔR = (dq) cos q R = cos q ΔR = -(dq) sin q R = tan q ΔR = (dq) sec2 q R = uncertainty logarithm base 10 ex ΔR = (Δx) ex R = e-x ΔR = -(Δx) e-x R = ln(x) ΔR = (Δx)/x Any measures of error may be converted to relative (fractional) form by using the definition of relative error. The fractional error in x is: fx = (ΔR)x)/x where (ΔR)x is the absolute ereror in x. Therefore xfx = (ΔR)x. The rules for indeterminate errors are simpler. RULES FOR ELEMENTARY OPERATIONS (INDETERMINATE ERRORS) SUM OR DIFFERENCE: When R = A + B then ΔR = ΔA + ΔB PRODUCT OR QUOTIENT: When R = AB then (ΔR)/R = (ΔA)/A + (ΔB)/B POWER RULE: When R = An then (ΔR)/R = n(ΔA)/A or (ΔR) = n An-1(ΔA) The indeterminate error rules for elementary functions are the same as those for determinate errors except that the error terms on the right are all positive. Students who are taking calculus will notice that these rules are entirely unnecessary. The determinate error equations may be found by differentiating R, then replading dR, dx, dy, etc. with ΔR, Δx, Δy, etc. This is equivalent to expanding ΔR as a Taylor series, then neglecting all terms of higher order than 1. This is a valid approximation when (ΔR)/R, (Δx)/x, etc. are all small fractions. The indeterminate error equations may be constructed from the determinate error equations by algebraic
the quantity. Uncertainty in logarithms to other bases (such as common http://phys114115lab.capuphysics.ca/App%20A%20-%20uncertainties/appA%20propLogs.htm logs logarithms to base 10, written as log10 or simply log) is this absolute uncertainty adjusted by a factor (divided by 2.3 for common logs). Note, logarithms do not have units.
\[ ln(x \pm \Delta x)=ln(x)\pm \frac{\Delta x}{x}\] \[~~~~~~~~~ln((95 \pm 5)mm)=ln(95~mm)\pm \frac{ 5~mm}{95~mm}\] \[~~~~~~~~~~~~~~~~~~~~~~=4.543 \pm 0.053\]known or estimated uncertainties. The calculations may involve algebraic operations http://web.mst.edu/~gbert/JAVA/uncertainty.HTML such as: Z = X + Y ; Z = X - Y ; Z = X x Y ; Z = X/Y ; Z = XY or mathematical functions of the type: Z = 1/X ; Z = ln(X) ; Z = log10(X) ; Z = 10X error propagation ; Z = eX ; Z = sqrt(X) . If uncertainties (dX, dY) are provided for the input quantities (X,Y), the program will perform the operation or function to calculate the answer (Z) and will also calculate the uncertainty in the answer (dZ). The program will assume the value has no propagation of error uncertainty if an uncertainty is not provided. Operation: Position the cursor on the blank under "X", click the mouse, and type a value. Alternately, press the TAB key until the cursor appears in this blank, then type the number. In case of an error, use normal text-editing procedures. Enter values for X and dX, and possibly for Y and dY. (The TAB key moves the cursor through the blanks in the order: X, dX, Y, dY). Click on the button for the desired operation or function. The equation for the calculation appears in the central blank, and the values of Z and dZ appear in their respective blanks. There are buttons for transferring values from Z to a MEMory location, or to the blanks for X or Y; or from the MEMory to X or Y. top
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