Draw schematically the diffusion coefficient d in a log scale versus 1/t (t is temperature in kelvin) for diffusion (i) within crystal bulk, (ii) along grain boundaries, and (iii) on crystal surfaces. briefly explain the reasons why the slopes are different.

answer : a model is often used to explain and make things easier to understand when any scientific topic needs to be demonstrated and explained.

as in this case where a scientist wants to use a model to present the results of his detailed scientific investigation. he should do it as it will him to make the audience understand the concept in a much better way. also, it can be changed according to new scientific understandings.

i'm pretty sure its b i might be wrong though!

in the analysis of systems that involve fluid flow, we frequently encounter the combination of properties u and pv.