Solid State Physics

Solid State Physics is the branch of physics that deals with the physical properties of solid materials, especially the electromagnetic, thermodynamic, and structural properties of crystalline solids.

2,846 Questions
Solid State Physics

What is dislocation density?

Dislocation density is the areal density of dislocations intersecting a plain, usually the free surface, given as number per cm2.

It may also be the volume density of dislocation line segments, given as the total length of dislocations divided by the containing volume (also 1/cm2), but this is rarely used in semiconductor physics, and more frequently found in engineering.

Dislocation density is typically measured by etching the free surface to form pits around the location at which the dislocation breeches the surface, and is termed etch pit density, or EPD.

Solid State Physics

What affects electrical resistance?

Primary Factors:
For a simple system like an electrical wire, there are three major things which will affect the electric resistance.
1. Resistance of wire conductor depends upon the material of which it is made.
2. Resistance of wire conductor is directly proportional to its length.
3. Resistance of a wire conductor is inversely proportional to its area of cross-section. (At least for low frequency voltage.)

In general every material has a characteristic electrical conductivity (and resistivity) which determines how well it will conduct electricity. Metals have very high conductivities and insulators very low. The geometry of an object affects the resistance with the above-mentioned wire geometry being the most important example.

In general the type of material and the geometry are the primary factors in determining the resistance of an object, but there are other effects worth mentioning.

Temperature can change electrical properties of a material and there are some dramatic examples such as superconductors. Semiconductors can also have important temperature dependent properties. For most generic materials there is a rise in resistance with an increase in temperature but the effect is not usually large.

More exotic phenomena also exist, such as the change in resistance due to a magnetic field or nonlinear conductors which do not have a fixed resistance but rather have a resistance that depends on voltage. Conductivity through a gas is a dramatic example of the latter.

Solid State Physics
Sound Waves

How many decibels do you need to break glass?

It is not so much the volume of the sound as the frequency as well. Sound at the wrong frequency can be played as loud as you like and it will not break the glass. The sound needs to be the same frequency as the resonant frequency of the glass (tap the glass, that note is it's resonant frequency). Once the resonant frequency has been found, it does not take much volume at all, even humans can do it, albeit trained singers (see Mythbusters).

Solid State Physics

Why electron does not exist in band gap?

Short Answer:

Electrons are waves and waves in a confined geometry can exist only with specific allowed wavelengths. This is true for sound waves in musical instruments, water waves in a ripple tank, light waves and electron waves in solids. Bad gaps and allowed wave regimes exist for all waves and are the consequence of simple reflection, refraction and interference.

Long Answer:

Electrons in crystals (not all solids, but only regular periodic arrays of atoms) have energies that restricted to certain allowed values or ranges of values called "bands" or "energy bands" and not other values called "gaps" or "band gaps" for a simple reason. Electrons are waves and electron dynamics is described by a wave equation, specifically the Schroeding equation. Quantum waves must respect the same dynamics as all waves and that includes the processes of reflection, refraction, and interference. It is these processes that create the bands and band gaps.

If you are asked to explain why a musical instrument gives out specific notes and not all possible sounds, you explain it as a condition of wave dynamics. A guitar string, for instance, vibrates with waves that can exist with whole wavelengths that fit within the length of the string. That is completely analogous to the phenomena that forces the existence of bands and band gaps for electrons in solids.

In fact, if you scale things up to wavelengths appropriate to sound (Sound wave are about a trillion time larger than electron waves.) you will get bands of allowed sound and band gaps where sound is not allowed. You can create a volume of space with a regular array of objects that reflect and refract sound and in that space only certain bands of wavelengths of sound will be allowed. The phenomena is the same. The equations are the same. The cause is the same.

Though quantum mechanics is strange and complicated, the reason energy bands in crystals exist is simple and completely faithful to the analogy of notes from a musical instrument.

Caveat: Though the existence of bands follows from this simple explanation, the prediction of the behavior of electrons in particular solids requires a sophisticated description of the particular atomic and electronic interactions. One can spend a career as a physicist making such descriptions and explaining the properties of the various kinds of solids.

More Answers:

Electrons may only possess specific energies. Another way of saying this is that they can only occupy certain energy levels. A band gap is a continuous spectrum of energies where no such energy levels exist. The band gap is simply a range of energies that the electron cannot have.

If you want to know why there are energies the electron can have and why there is a gap in between these energy ranges then that's quite a bit more complicated. A short answer would be that there are gaps because there are asymmetries in the basic repeating unit of the crystal structure but I appreciate that that probably prompts a bunch of other questions.

Snow and Ice
Solid State Physics

Why is snow a crystalline solid?

yes, each snowflake is one dendritic ice crystal.

However fallen snow is not a solid, the snowflakes have stacked up to capture a larger volume of air than the volume of the snowflakes themselves.

Solid State Physics

Why is it easier to push an empty box?

less friction

Electronics Engineering
Solid State Physics

Why semiconductors are used for making electronic devices?

The main reason semiconductor materials are so useful is that the behavior of a semiconductor can be easily manipulated by the addition of impurities, known as doping. Semiconductor conductivity can be controlled by introduction of an electric or magnetic field, by exposure to light or heat, or by mechanical deformation of a doped mono-crystalline grid; thus, semiconductors can make excellent sensors. Current conduction in a semiconductor occurs via mobile or "free"electrons and holes. collectively known as charge carriers. Doping a semiconductor such as silicon with a small amount of impurity atoms, such as phosphorus or boron. greatly increases the number of free electrons or holes within the semiconductor.

It can be make in very small size and the electronics device are small in size that why the semiconductors are used in electronic devices.

The above explains HOW semi conductors work.

The reason for WHY they are used is, what's the alternative?

The only alternative is thermionic valves (tubes).

Tubes fell out of favour for many reasons.

They run hot

Made of glass and delicate,



Consume lots of power

Need high voltages.

Semi conductors are the opposite of all of these.

Solid State Physics

What are all the objects that can be compressed?

All objects can be compressd unless they are in a liquid state.

Solid State Physics

What are examples of at least 6 physical changes?







Solid State Physics

Do molecules speed up or slow down when melting?

Neither, they keep the same speed.

When a normal solid melts, and ice is as normal as anything else, the liquid portion grows and the solid portion shrinks, but the temperature remains the same. Since temperature is proportional to the kinetic energy of the particles in the system, the particles in the liquid portion and particles in the solid portion have the same temperature ans the same kinetic energy and hence the sames speed,

As more heat is applied and the melting is complete, temperature rises and kinetic energy of the molecules starts increasing again.

Electricity and Magnetism
Solid State Physics

What are some good conductors of electricity?

Metals are good conductors of electricity, with silver being the best. Graphite and solutions of ionic compounds are also good.

Electricity and Magnetism
Solid State Physics

What is the definition of conductors and insulators?

A conductor is a material that can transfer energy efficiently and and insulator is the opposite.

Conductor means something that blocks it and insulator means something that can go through it

A conductor easily transfers energy in the form of electricity and/or heat, while an insulator does not easily transfer these types of energy.

In electricity, a conductor is a material that can let current pass through and an insulator does not let current pass through,or rather copper is a conductor and plastic is an insulator.

A insulator is something that will not allowheat/electricity to pass through it and a conductor is something that allows heat/electricity to pass through it.

Electrical Engineering
Solid State Physics

Why does resistance cause conductors to get hot?

Electronics Engineering
Solid State Physics

What are the advantages of cmos over bipolar counterpart?

Lower power dissipation (except at very very high switching rates, as almost all the power dissipated by CMOS is during switching).

Solid State Physics
Periodic Table

What is the most resonant metal?

If resonance is related to hardness (and it is) then the most resonant metal would be Beryllium.

Solid State Physics
Quantum Mechanics

What is Planck's quantum theory?

Max Planck assumed that the radiation energy is emitted in discrete packets called quanta rather than in a continuous way. The energy E of the quantum is related to the frequency ν by E = hν. The quantity h, now known as the Planck constant, is a universal constant with the approximate value of 6.626 X 10^-34 Js

Solid State Physics

What is lattice dielectric constant?

The contribution of the positive ions in the lattice to the dielectric constant (e.g. Cadmium Selenide).

Solid State Physics

Why some phonons are called optical phonon?

because their frequency in the range of infra-red 10^13 HZ.

Solid State Physics
Quantum Mechanics
Thermodynamics and Statistical Mechanics

What is phonon theory?

sound and other mechanical vibrations are quantized as bosonic particles called phonons.

Solid State Physics
Elements and Compounds

What is the microstructure of aerogel?

Very tiny bubbles of air in a very thin walled ceramic matrix. In other words ceramic foam.

Electricity and Magnetism
Solid State Physics

Which metal has highest resistance to electric current flow?

It appears that Plutonium has the lowest conductivity (highest resistance) of all the metals, at 106 /Ohm*cm.

This information comes from the link below.

Solid State Physics

How does halving the sample affect the density?

Not at all. The density remains the same.

Solid State Physics

Could you drink from a glass without friction?


Solid State Physics

Which expands more for increases in temperature solids liquids or gases?


Electronics Engineering
Electromagnetic Radiation
Solid State Physics

What is the purpose of a led?

An LED (light emitting diode) is used in electronic circuits to provide light where needed. Essentially, it is a low power lightbulb, which uses a gallium nitride/ indium phosphide P-N junctions to create light. They can be used in circuits to indicate that power is being supplied (the small light on your PC's motherboard). They have more practical uses too. High-power LED's are used as an alternative to light bulbs in some places, they are used as bicycle lights too.


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