This set of Materials Science Multiple Choice Questions & Answers (MCQs) focuses on “Steady State Diffusion”.
1. In steady state diffusion which of the following remains constant?
a) Concentration gradient
b) Kinetic energy of particles
c) Potential energy of particles
d) Change of concentration with respect to temperature
Explanation: In steady state diffusion, the concentration of the diffusing with respect to space at any point remains constant. Kinetic energy and potential energy need not be constant.
2. Which of the following gases can be purified by allowing it to diffuse through palladium cap?
Explanation: When a gas at constant pressure pervades through a thin walled metal foil, steady state diffusion occurs. Hydrogen is purified by making it pass through a palladium cap after going through steady state diffusion.
3. Which of the following law is used for steady state diffusion?
a) Fick’s law
b) Newton’s law of diffusion
c) Bragg’s law
d) Charles’s law
Explanation: Fick’s law is used under steady state conditions to obtain the diffusion coefficient. Bragg’s law is used in diffraction of light while Charles’s law is used in thermodynamics and is also known as the law of volumes.
4. Which of the following is not a part of Fick’s first law?
a) Diffusion flux
b) Diffusion coefficient
c) Change in concentration with respect to the position in space
d) Change in concentration with respect to time
Explanation: Fick’s first law is given by: J = – D (dc / dx), where J is diffusion flux or diffusivity, D is diffusion coefficient and dc/dx stands for change in concentration with respect to the position in space. Hence change in concentration with respect to time is not a part of Flick’s first law.
5. Velocity of diffusing particles does not depend on _______
b) Viscosity of the fluid
c) Size of the particles
Explanation: Diffusion coefficient is proportional to square of velocity which depends on the temperature of the fluid, viscosity of the fluid and the size of particles. The velocity of particle does not depend on pressure.
6. Flux direction is opposite to the direction of the concentration gradient.
Explanation: Flux direction is opposite to the direction of the concentration gradient. Because of which there is a negative sign in Fick’s first law of diffusion on the right side of the equation.
7. The diffusivity of copper in copper increases by how many times when the temperature is increased from 500 ° C to 1000 °C?
Explanation: The diffusivity of copper in copper at 500 °C is 1e-18 while diffusivity at 1000 °C it is 2e-13. By dividing the values, we find that the diffusivity increases by 200000 times fold.
8. What is the shape of the graph for steady state diffusion where the concentration of diffusion species is in the y-axis and position is in x-axis?
d) Straight line
Explanation: The concentration of the diffusing species is directly proportional to position. Hence graph is a straight line with negative slope.
9. In dilute aqueous solutions which of the following can be the value of diffusion coefficient at room temperature?
Explanation: The diffusion coefficient in a dilute aqueous medium for most ions lies in the range of 0.6e-9 to 2e-9 m2/s. Only 0.7e-9 lies in the range while the others are beyond the range and hence it is the answer.
10. There is no difference between diffusion and net diffusion.
Explanation: In homogeneous mixture diffusion and net diffusion are same but in case of in homogeneous materials the effect of diffusion is seen to be changing in concentration with time and hence in this case the net diffusion and diffusion values are different.
Sanfoundry Global Education & Learning Series – Materials Science.
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