In this context, what does the symbol D represent?

In this context, what does the symbol D represent?

• A. The coefficient of oxygen movement
• B. The diffusion constant
• C. The solubility of water
• D. The oxygen partial pressure

Answer: (A)

The symbol D is the diffusion coefficient, describing how readily oxygen moves through the lens material when there is a concentration gradient. It’s the material property that sets how fast oxygen can diffuse, and it appears in Fick’s law as the factor linking flux to the concentration gradient (J = -D dC/dx). This is different from solubility, which tells you how much oxygen can dissolve at a given pressure (the amount that can be in solution), and from oxygen partial pressure, which is the driving force for diffusion. In many texts, D is also called the diffusion constant, and it essentially conveys the same idea as the coefficient of oxygen movement.

The symbol D is the diffusion coefficient, describing how readily oxygen moves through the lens material when there is a concentration gradient. It’s the material property that sets how fast oxygen can diffuse, and it appears in Fick’s law as the factor linking flux to the concentration gradient (J = -D dC/dx). This is different from solubility, which tells you how much oxygen can dissolve at a given pressure (the amount that can be in solution), and from oxygen partial pressure, which is the driving force for diffusion. In many texts, D is also called the diffusion constant, and it essentially conveys the same idea as the coefficient of oxygen movement.