# solids

1. ### I Relation between the momentum operator and the Hamiltonian gradient operator

Is there a relationship between the momentum operator matrix elements and the following: <φ|dH/dkx|ψ> where kx is the Bloch wave number such that if I have the latter calculated for the x direction as a matrix, I can get the momentum operator matrix elements from it?
2. ### Mechanics of Solids - weight problem

Summary: How much weight can the bars support? Three one-meter-long bars with cross-section area A = 1 square centimeter support a rigid plate of weight W. For steel, E = 200 GPa and S = 400 MPa. Determine the maximum weight W the bars can support for three cases: (i) all three bars are...
3. ### B Can you change the state of matter by increasing the speed?

We all know that the state of matter can be changed by increasing temperature or by applying pressure. And, all of these, in some way lead to a change in the particles' speed. The speed of the particle decides the state of matter. So, if we were to throw an object at very high speeds, like 50%...
4. ### Can diffusion occur in solids?

I see in most newer syllabus textbooks it says that diffusion is the mixing of fluids and diffusion cannot occur in solids But when is search the web I see lectures and books written on the title diffusion in solids and when I studied I was taught that diffusion occurs in solids but at very very...
5. ### I Question about the Debye model of solids

Hi all, I have trouble understanding some ideas relating to the Debye model. In my text (Oxford Solid State Basics by Steven Simon, page 11), it was stated that Debye wrote the following expression \langle E \rangle = 3\sum_{\vec{k}} \hbar \omega (\vec{k}) \ [ n_B (\beta \hbar \omega...
6. ### I Questions on Debye's Model of solids

Hi all, I have a few questions related to Debye's model of solids. Any assistance is greatly appreciated. $\textbf{1)}$ My current understanding is that unlike Einstein's model, he views a 1D solid as a chain of atoms similar not unlike a 1D chain of masses coupled with springs. Thus a chain...
7. ### Band diagram, conductivity tensor

Hello! Does anyone have an idea of how can I obtain information from a band diagram about the directions along which the system conducts best and worst ? Thank you in advanced! :)
8. ### Heterogeneous equilibria: concentration of solids issue

1. Homework Statement Hello! Here is the quote from the chemistry textbook by Tro: However, since carbon is a solid, its concentration is constant—it does not change. Adding more or less carbon to the reaction mixture does not change the concentration of carbon. The concentration of a...
9. ### A solid cylinder of uniform density of 0.85 g/cm3 floats in

1. Homework Statement A solid cylinder of uniform density of 0.85 g/cm3 floats in a glass of water tinted light blue by food coloring. https://s1.lite.msu.edu/res/msu/kashy/physicsLib02/32_Fluids1_Pascal_Arch/graphics/archimedes.gif Its circular surfaces are horizontal. What effect will the...
10. ### Can all gases be ionized to make a plasma?

I sort of new to the states of matter, so please use English (explain what all the big words mean). First of all what does ionizing even mean? second every type of matter of 4 states?
11. ### Radii of Mg2+ and O2- in MgO

1. Homework Statement Below is an image of a unit cell for MgO. Does MgO have the lattice structure of NaCl or ZnS? If the density of MgO, $\rho$ = 3,58g/cm3, evaluate the sizes of the radii of Mg2+- and O2--ions. Answers: 149pm and 62pm 2. Homework Equations 3. The Attempt at a...
12. ### Reworking of the Drude model using scattering statistics

1. Homework Statement The problem I have been set is to rework the Drude model using clearly defined scattering statistics. 2. Homework Equations The Drude model as we have been given it is in terms of momentum \vec{p}(t+dt)=(1-\frac{dt}{\tau})(\vec{p}(t)-q\vec{E}(t)dt)+(\frac{dt}{\tau})(0)...
13. ### Calculate variation in volume using given Poisson's ratio

1. Homework Statement : A cylinder is elongated by 2% of its original length. If Poisson's ratio of its material is 0.3. Calculate the percentage variation in volume. 2. Homework Equations V = πr^2l η= 0.3= Δl/l/Δr/r 3. The Attempt at a Solution I tried using calculus to differentiate V to...
14. ### Trouble with Gibbs free energy equation

Hi everybody! Lately I tried to overcome some problems with understanding thermodynamics laws, and unfortunately I couldn't find anything about my question:nb) and I really hope someone can help me here... My question is: This version of Gibbs formula dG= VdP-SdT, can be applied to any close...
15. ### Gasoline smell does not inginte

Say there is a chair soaked in gasoline. If someone is to walk in the room the smell is immediate if the chair was lit on fire the liquid gasoline would ignite the chair. However, what about the particles that constitute the smell of it? Why don't they ignite as well? What is the nature of the...