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4
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1answer
332 views

Impurity scattering temperature dependence

Is there any temperature dependence of relaxation time in impurity scattering of conducting electrons? It seems to me that there is none. But, some people claim that there is. So if you could ...
2
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2answers
2k views

Properties to select suitable materials for making permanent magnets

I have read that soft iron is suitable for making a permanent magnet. Because it is required for permanent magnet to have high coercivity and high retentivity. Same text also said earlier that soft ...
0
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0answers
12 views

relation between chemically activity and work function and fermi level

I am trying to connect the following concepts together : "being chemically active", "work function" and "fermi level" I want to know if for a metal, "being chemically active" is equivalent to "its ...
2
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2answers
25 views

Is there any relation between temperature dependence of resistance and fermi energy in metals?

Given that the resistance varies linearly with temperature in metals, is there any way we can calculate the Fermi energy from this information?
0
votes
1answer
19 views

currents in an isolated metal exposed to an alternating uniform electric field

For example, let's look at a metal sphere between a capacitor's (infinite) plates. Let's run an AC current through the capacitor, resulting in an oscillating electric field. The charges will move in ...
8
votes
1answer
148 views

Third-order susceptibilities of metals?

Can anyone point me to a source for measurements of the third-order nonlinear electric susceptibilities $\chi^{(3)}$ of various metals? Specifically in relation to the AC Kerr effect, so measurements ...
7
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3answers
198 views

Why are permanent magnets permanent?

Let me see if I get it right. When an iron bar is attracted by a permanent magnet it becomes a magnet itself because all of its magnetic domains start to point in the same direction. When the iron bar ...
3
votes
1answer
93 views

Do Shape Memory Alloys (SMA) work harden?

We had a piece of this thin Shape Memory Alloy in class, (I think it was called nitinol, but I think thats a brand name) the teacher showed how it is very flexible and springy, and will return to it's ...
1
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0answers
20 views

Lindhard function for surface plasmon

Is there anybody that knows how to calculate the Lindhard function for the surface plasmon (between the surface of two metals of different dielectrics)? What I'm looking for is to find this function ...
5
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2answers
9k views

Why does magnet attract iron but not other metals?

While searching, i found this page: http://timesofindia.indiatimes.com/home/stoi/Why-does-a-magnet-attract-iron/articleshow/4298171.cms but it does not have full explanation. So Please tell full ...
0
votes
1answer
90 views

Grain boundary sliding in creep

To prevent grain boundary sliding so that creep is less likely to occur, usually engineers would design components of larger grains or have columnar grain structure to prevent grain-boundary sliding. ...
14
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1answer
3k views

When heat is applied to the top of a stack of pennies, why does the bottom penny melt first?

I just watched this video where a blow torch is used on the top of a stack of pennies. I'd like to know why the bottom penny melted first.
48
votes
6answers
8k views

Why are most metals gray/silver?

Why do most metals (iron, tin, aluminum, lead, zinc, tungsten, nickel, etc.) appear silver or gray in color? (What atomic characteristics determine the color?) What makes copper and gold have ...
0
votes
1answer
78 views

Is there any material that is NOT conductive and IS magnetically attractive?

Is there any material which is NOT conductive and IS magnetically attractive? I am in need of a material which I can shape and use within a machine. It must be very attracted to magnets similarly to ...
1
vote
1answer
165 views

Semiclassical description of EM waves reflection from metallic surfaces

Imagine an EM wave impinging on a metal. Fresnel's formulas tell us that no wave can propagate through the metal, or that the transmitted field is an evascent wave with some penetration depth ...
8
votes
2answers
536 views

Why does Platinum evaporate if left long enough?

I have been reading into research relating to the redefining the 1 kg weight as the current Platinum-Iridium is becoming smaller. In this article, here, it mentions that the original metal weight ...
1
vote
2answers
52 views

Can work hardening of a metal be avoided?

My left earbud recently broke mid-wire: the bit that I like to fiddle with and bend. I fixed it, but I was wondering whether there are metals that don't work harden, or resistant to it? Is there a ...
5
votes
1answer
1k views

Why does a gold leaf appear blue if made very thin?

Is this to do with excitation of electrons and emission of photons? Or is it more to do with the structure of the gold I.e. Only small wavelengths being able to pass through gaps between atoms? EDIT: ...
1
vote
1answer
56 views

Can metal rods detect underground wires?

Until not long ago, I was working in the drilling and infrastructure business. Some people I was working with used metal rods as a "quick and dirty" method of detecting underground wiring, before ...
1
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0answers
14 views

Does illuminating a conductor with light energy less than its workfunction change the measured conductivity?

For example, does the light absorbed in an exposed metal wire increase the average velocity of the electrons, hence increasing mobility and conductance?
2
votes
1answer
8k views

Why is stainless steel a poor conductor of electricity?

I recently had a metal plate put in my shoulder and was wondering why stainless steel isn't a good conductor (At least I hope it isn't). Does the alloy just lack free electrons? Why is that?
1
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4answers
63 views

Measuring electric conductivity

My daughter is doing a science experiment on which metal (e.g., copper, silver, aluminum, iron) has maximum electric conductivity. We are assuming we can accomplish this by using different metal, 3 to ...
3
votes
1answer
61 views

Why are some elemental materials grey?

How does grey occur in elemental materials such as metals? I believe that grey arises from the simultaneous reflection and absorption of all colors of the spectrum (in different atoms of course), as ...
0
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0answers
35 views

Free vs Bound Charges, especially in metals

Are conduction band electrons in metals generally considered free charges or bound charges for E&M purposes? I'm not asking about freedom in the sense of being able to escape the potential well ...
1
vote
2answers
118 views

Why does room temperature water and metal feel almost as cool as each other?

From what I've read about heat, temperature and conductivity, I understand that the reason water at room temperature feels colder than most other things at the same temperature (like wood, air, ...
0
votes
1answer
65 views

What will happen if I throw chocolate figure on hot red fan?

What will happen if i throw chocolate figure on hot red fan. Fan, of course, is sucking in my figure, but will it evaporate, or it will be thrown away in liquid form? Lets take fan with steel blades, ...
4
votes
1answer
79 views

materials that repel positrons?

In this article is discussed at some length positron formation in metallic surfaces. Positrons have work functions that describe how much energy they have to receive in order to be extracted from the ...
0
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0answers
28 views

Like viscoelastic polymers, why there are not storage and loss moduli for cast iron?

Viscoelastic polymers have different paths upon loading and unloading, so there is energy dissipation, so they have storage and loss moduli. Plastic behavior is also shown by cast iron: loading and ...
4
votes
3answers
83 views

What happens to the electrons when metal gets cut or broken?

For example, if I take an iron rod (or thread) and cut it in half, could it happen that one side remains with an extra electron or would it balance out too fast? If possible, do the parts simply ...
2
votes
1answer
66 views

How to calculate the speed of electrons in a metal

According to the Sommerfeld model, the electrons on the Fermi level has the relation $$ \epsilon_F=\frac{\hbar^2k_F^2}{2m_e}=\frac{1}{2}m_ev_F^2 $$ i.e. $\hbar k_F=m_ev_F$ with $k_F=(3\pi^2n)^{1/3}$ ...
0
votes
0answers
20 views

If an common metal is induced with a static dipole moment, won't the the positive side be weaker?

To my knowledge, common metals with metallic bonding is formed through free electrons within its lattice structure. If say we are to shift the free roaming electrons to one side and therefore minutely ...
4
votes
1answer
1k views

Why do most metals appear silver in color with gold being an exception from a scattering and EM viewpoint?

Related: Why are most metals gray/silver? After reading Johannes’ impressive answer to Ali Abbasinasab question of why do most metals appear silver in color with the exception of gold (and copper), ...
2
votes
1answer
36 views

Why does carbon alloy with iron specifically?

Everyone knows what an alloy is: it's a metal made by melting two (or more) other metals together. Unless of course you're talking about steel. That's a metal made by mixing carbon (very much not a ...
0
votes
0answers
14 views

Will a sodium bell ring clearly after being submerged in liquid nitrogen?

Lead is fairly soft at room temperature but rings clearly when cooled to liquid nitrogen temperatures. Sodium is even softer. If cooled to liquid nitrogen temperature, could it also ring?
0
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0answers
42 views

Physical sides of Electromagnetic Wave Propagation as nonlinear in metal

This Wikipedia page says that the electromagnetic wave propagation in air can be done by Freshnel transform: $$U_{0}(x,y) = - \frac{j}{\lambda} \frac{e^{jkz}}{z} \int\limits_{-\infty}^{\infty} ...
2
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0answers
47 views

Can I use ultrasound to detect metal underground? [closed]

I am doing research which aim to detect metal underground. I know that most metal detectors are based on the concept of change of inductance of an inductor caused by mutual inductance with a ...
1
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0answers
66 views

How can colors from heat tinting depend on temperature only?

Colors caused by heat tinting of a material can be listed by temperature. For example, for carbon steel: ...
178
votes
11answers
38k views

Why don't metals bond when touched together?

It is my understanding that metals are a crystal lattice of ions, held together by delocalized electrons, which move freely through the lattice (and conduct electricity, heat, etc.). If two pieces ...
19
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2answers
2k views
0
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0answers
16 views

Mechanism of Current flow in Metals [duplicate]

I do not fully understand the mechanism of current flow in conductors. It cannot be that a current starts only when an electron from one terminal of the electric supply physically reaches the other ...
1
vote
1answer
80 views

Cold welding of a metallic surface

I have heard of cold welding, it's said that it's only possible if the surface is very clean. Can cold welding be accomplished by shearing a metal object and then immediately touching the newly ...
2
votes
1answer
87 views

Electron density in metals at non zero temperature

When computing the electron density in metals, the usual crude result is computed for zero temperature. That is, we integrate \begin{equation} n=\frac{8\sqrt{2}\pi m^{3/2}}{h^{3}} ...
0
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0answers
27 views

Determining if an object is dielectric or metallic

In a worksheet I was given, I had to find the net electric field of P which is L distance away from a bar. The last question is ...
0
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0answers
61 views

Thermal fluctuations in metals

My professor said that the $k_BT$ displacement in the energy levels of the band electrons is due to the space-thermal displacement of the potential of the ion host. I think that this displacement is ...
4
votes
1answer
2k views

What tests can I do at home to identify any metal?

Regarding a question on another Stack Exchange site which identifies a weighted Lego brick to be some kind of metal, I wanted to know how to identify a metal, perhaps limited to household objects like ...
1
vote
1answer
82 views

How does the color of fine dispersed metal particles change between silver and black?

Small dispersed particles of metals are often black, while a solid object of the same material would be some shade of silver. The most notable example is the use of metallic silver as the black color ...
0
votes
1answer
63 views

A question about residual stress

Shot peening is a process of inducing residual compressive stress on the surface layer of metal parts. When shooting particles are colliding on the surface of metal there is a compressive stress. My ...
0
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0answers
31 views

Mixed-Alloy materials

Short version: Is it a physical problem (crystal structure/grains/redox/etc.) or just a logistics problem (keeping the solutes from homogenizing, molten/solid/temperature related problems) that keeps ...
-1
votes
1answer
39 views

Does it take a lot of energy to heat metals up?

Why does it take a lot of energy to heat metals? And to do it quicker it requires much more energy? What about the use of lasers would that be an efficient process that is quicker and requires less?
0
votes
0answers
10 views

Determining porosity in metals

I am in need of a book (preferably) or other reference material which would help technicians determine whether porosity exists in the fracture face of a tensile test bar for a variety of different ...