1. In steady state diffusion, which of the following remain unchanged with time?

a) Concentration at source

b) Concentration at sink

c) Concentration profile

d) All of mentioned

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2. For steady-state diffusion, diffusion flux is proportional to concentration gradient. Concentration gradient is:

a) Rate of change of concentration with respect to space

b) Rate of change of concentration with respect to time

c) Difference in concentrations at the source and sink

d) Ratio of concentrations at source and sink

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3. Which of the following is not true for steady-state diffusion?

a) The concentration profile is linear

b) The concentration gradient is constant

c) There is no net transfer of mass

d) The diffusion flux is constant

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4. Concentration of hydrogen gas across a 2mm thick palladium sheet differs by 4 kg/m^{3}. Considering steady-state diffusion with diffusion constant 10^{-10} m^{2}/s, diffusion flux is ______ kg/m^{2}.s:

a) 2 x 10^{10}

b) 2 x 10^{-10}

c) 5 x 10^{-11}

d) 5 x 10^{9}

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5. The expression J = M/(A.t), where J, M, A, & t are diffusion flux, mass of diffusing species, cross sectional area, and time respectively is:

a) incorrect

b) valid for steady-state diffusion only

c) valid for non steady state diffusion only

d) valid for both steady and non steady state diffusion

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6. If C is the concentration of the diffusing species at distance x from the source and time t, then according to Fick’s second law (assuming diffusion coefficient, D is constant):

a) ∂C/∂x = D.(∂C/∂t)

b) ∂C/∂t = D.(∂^{2}C/∂x^{2})

c) ∂C/∂x = D.(∂^{2}C/∂t^{2})

d) ∂C/∂t = D.(∂C/∂x)

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7. The relation between temperature and diffusion coefficient is:

a) Linear

b) Exponential

c) Sinusoidal

d) Diffusion coefficient is not related to temperature

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_{0}.exp( -Q

_{d}/ R.T) where D

_{0}is diffusion coefficient at initial temperature, Q

_{d}is the activation energy, R is gas constant, and T is the change in temperature.

8. Predeposition and drive-in diffusion are two heat treatments used in manufacture of integrated circuits.

Assertion: Predepostion is carried at higher temperature than drive-in diffusion.

a) True

b) False

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9. Following plot shows the concentration profile at two different time, T1 and T2 for the same non-steady diffusion process.

What is the correct relationship between the two?

a) T1 > T2

b) T2 > T1

c) Insufficient data

d) Same process can’t have two concentration profiles

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10. Diffusion through grain boundaries is very fast and is called short-circuit diffusion.

Assertion: Their contribution to overall diffusion is negligible.

a) True

b) False

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