Question

Fick’s law describes:

• A. Heat flow in solids
• B. Fluid flow in pipes
• C. Molecular diffusion
• D. Radiation exchange

Hint:

Fick → Diffusion, Fourier → Heat conduction, Newton → Cooling.

Answer 1

The Correct Option is C

Concept: Fick’s law is a fundamental law in mass transfer that describes the rate of diffusion of a substance due to a concentration gradient.

Step 1: Statement of Fick’s First Law.
Fick’s law states: \[ J = -D \frac{dC}{dx} \] where:
• $J$ = diffusion flux
• $D$ = diffusion coefficient
• $\frac{dC}{dx}$ = concentration gradient

Step 2: Understanding the equation.
The negative sign indicates that diffusion occurs from higher concentration to lower concentration.

Step 3: Physical interpretation.
Fick’s law explains:
• Movement of molecules due to concentration difference
• Mass transfer in gases, liquids, and solids

Step 4: Evaluating options.
• Heat flow in solids — Described by Fourier’s law
• Fluid flow in pipes — Described by fluid mechanics (Bernoulli/Navier-Stokes)
• Molecular diffusion — Correct
• Radiation exchange — Described by Stefan-Boltzmann law

Step 5: Final reasoning.
Since Fick’s law directly relates to diffusion phenomena, option (3) is correct. Final Conclusion:
Fick’s law describes molecular diffusion. Hence, the correct answer is option (3).