# PHY 125 – Lecture 3

Published on: Sat Jan 30 2010

**Percent Uncertainty** = ∆A/A * 100
This is also known as fractional uncertainty. I wrote this out in more detail in HW1 Notes & Concepts.
**Addition and Subtraction of Uncertainty**
∆D = ∆A + ∆B
**Multiplication and Division of Uncertainty**
∆D/D = ∆A/A + ∆B/B
The fractional uncertainty of multiplication and division is the sum of fractional uncertainties. From there calculate backwards to get ∆D.
**Things to Look for**
Minimum with Uncertainty
Maximum with Uncertainty
Most Likely with Uncertainty
**Uncertainty with Angles**
sin(33º ± 1º)
sin ( x ± ∆x)
sin x ± ∆(sin x)
∆(sin x) / sin x
**Rough Estimates (Order Of Magnitude)**
Is your answer reasonable?
Use Order Of Magnitude to quickly estimate