Nitrogen from a gaseous phase is to be diffused into pure iron at 675C. If the surface concentration is maintained at 0.2 wt% N, what will be the concentration 2 mm from the surface after 25 h? The diffusion coefficient for nitrogen in iron at 675C is 2.8 1011 m2 /s.
PY 205 with Daniel Dougherty Week 1 Chapter 1 1/12/2016 Theory – broader, more detailed and can give quantitatively testable predictions, often with great precision Law – certain, concise but general statements about how nature behaves Principle- less general statements o Scientific laws are descriptive because they describe how mature behaves Uncertainty and percent uncertainty o Ratio of uncertainty to the measured value X 100 to make it a percent o Ex: 8.8 +/- .1cm .1/8.8 X 100 = 1% Significant figures o 0 is a placeholder o Ex: 80 one significant figure since 0 does not count o RULE: number of significant figures in the last number should be the s
