# Physics 212, 2018: Lecture 24

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• Fick's first law of diffusion ${\displaystyle J=-D{\frac {d\phi }{dx}}}$ or ${\displaystyle {\vec {J}}=-D\nabla \phi }$ (also known as Newton's law of cooling if ${\displaystyle \phi =T}$, or the Fourier law of heat conduction)
• Fick's second law of diffusion ${\displaystyle \partial _{t}\phi =-D\nabla ^{2}\phi }$.