Table of Contents

• Prequiz...
• Just Plain Movement
• 1: Measuring movement
• 2: Directed vs. undirected movement
• 3: Measuring movement using flux
• Introducing Gradients
• 4: Gradients and diffusion
• 5: Watching diffusion happen (applet)
• 6: Visualising the Gradient
• Fick's Laws, Part I
• 7: Fick's First Law
• 8: The gradient in Fick's First Law
• 9: A familiar equation for Fick's First Law
• 10: Graphing Fick's First Law
• 11: How does flux depend on distance?
• 12: A fragrant example
• 13: General transport equations and Fick's First Law
• Review
• 14: Summary

General Transport Equations and Fick's First Law

Before we move from Fick’s First Law to his (creatively named) Second Law, it is worth noting that Fick's Law is really just one of several “transport equations” that all have a common form. In these equations, J stands for transport (of particles, charge, or heat). So you can see that the same equation that we have been learning about is applicable in almost the exact same form in several different fields!

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Diffusion	where J is the flux, D is the diffusion coefficient, C is the concentration of particles, and x is the distance.

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For Charge	where V is voltage, so the flux of ions (J) is directly proportional to the difference in voltage (the voltage potential), and σ (also called electrical conductivity) is a coefficient that relates to the properties of the medium the charge is traveling through.

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For Energy (heat)

where T is temperature (Kelvin), so that heat transfer (J) is directly proportional to the difference in temperatures, and k is called the coefficient of thermal conductivity.