# What is Insulator: Definition and 129 Discussions

An electrical insulator is a material in which electric current does not flow freely. The atoms of the insulator have tightly bound electrons which cannot readily move. Other materials, semiconductors and conductors conduct electric current more easily. The property that distinguishes an insulator is its resistivity; insulators have higher resistivity than semiconductors or conductors. The most common examples are non-metals.
A perfect insulator does not exist because even insulators contain small numbers of mobile charges (charge carriers) which can carry current. In addition, all insulators become electrically conductive when a sufficiently large voltage is applied that the electric field tears electrons away from the atoms. This is known as the breakdown voltage of an insulator. Some materials such as glass, paper and Teflon, which have high resistivity, are very good electrical insulators. A much larger class of materials, even though they may have lower bulk resistivity, are still good enough to prevent significant current from flowing at normally used voltages, and thus are employed as insulation for electrical wiring and cables. Examples include rubber-like polymers and most plastics which can be thermoset or thermoplastic in nature.
Insulators are used in electrical equipment to support and separate electrical conductors without allowing current through themselves. An insulating material used in bulk to wrap electrical cables or other equipment is called insulation. The term insulator is also used more specifically to refer to insulating supports used to attach electric power distribution or transmission lines to utility poles and transmission towers. They support the weight of the suspended wires without allowing the current to flow through the tower to ground.

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1. ### Gauss' law for a cavity in an insulator

This is a problem from Yale OCW (Shankar). The solution he gives is as follows: Sure, this makes sense. However... Superimposed rho and negative rho with radius R/2 means there is no charge enclosed in the cavity... therefore no charge -> no flux -> no electric field.
2. ### I Question about the current through a strong insulator

Suppose we put a strong insulator under our feet. In this case, when we connect the test light to the electrical outlet, the light of the test light lights turn on. I wonder how the electric current can pass through the strong insulator. If we calculate, the electric current cannot be more than...
3. ### I Can an insulator reflect radiowaves?

So, when a radiowave strike a surface, whether the wave get reflected or not depend a lot on the characteristic impendence of it. If the radiowave travel from free space to a material. Any mismatch from the approx. 377 ohms impedance of free space (Z0) will result in a reflected wave; the...
4. ### Resistance calculation -- Comparing coax cable insulator resistances

Since both cylinders have the same material, this implies the density is the same. Length is also the same based on the question. We only need to compare the radii for resistance. R2 = pi ((2b)^2 - (2a)^2) R1 = pi (b^2 - a^2) R2/R1 = 4, so my answer is C. But, the given answer is A. Where did I...
5. ### Charged metal ball wrapped in rubber or other insulator

If I have a metal electric conducting ball the size of an average snowball (Happy Holidays) and give it a charge of say 0.1 Coulombs and set it on a wooden table, will it ever discharge if not touched by anything else? If so, if it is wrapped in an electrical insulator, will it ever discharge...
6. ### Optimizing Insulator Spacing for High Strength Busbar Systems

Well, I have one nice problem. I have 30x10mm busbar, and Isc=30kA. I must place this busbars in electrical panel, but I have a problem with insulators. Can I use a red insolators as it's showed on picture, or I should use special holders for busbar system. Another problem is: When I use such...
7. ### Exploring the Effects of an Insulator Between Two Diodes

What would happen if we put two diodes together with an insulator in between? p/n/insulator/p/n
8. ### Why can an electron go through PVC insulator

I connected a PVC insulated alligator clip test lead to a 12V (give 20V) DC power supply positive terminal and a multimeter. After that I connected an other one to the multimeter ground, and a third one to the power supply negative terminal. I turned the multimeter to DC V measure mode. When I...
9. ### High dielectric strength insulator

Hello! I would need advice on insulator material I can use for an ion Thomson Parabola spectrometer. I would need to use an insulating sheet of 225x600x1,5mm and a smaller sheet of 100x100x1,5mm I found PBN having an incredible dielctric strength, but seems like it cannot be manufactured in...
10. ### Potential across a conducting sphere surrounded by an insulator

Homework Statement A conducting sphere has a radius of 2.25 m and carries a positive surplus charge of 35.0 mC. A protective layer of barium titanate is applied to the surface of the sphere to make it safe for laboratory workers nearby. Safety considerations dictate that the potential...
11. ### Ansys Maxwell -- how to ground an insulator?

Can anyone guide me about how to ground an insulator using Ansys Maxwell 2015?
12. ### A Metal or Insulator: Examining Resistance in Multiple Directions

Generally, a material is metal or insulator is simply determined by the gap. But if we view it in another way, to measure the resistance in different direction, says x and y, and there are usually different. And then measure the resistance change with temperature. Usually, the resistances goes...
13. ### I Charged insulator with electrons throughout its volume?

Could one make a negatively-charged insulator with the extra electrons trapped all the way through its volume by building it up layer by layer with electrons "sprayed" onto each layer as it was constructed? I guess the electrons would be trapped in empty atomic orbitals within the material - is...
14. ### A Is there a topological insulator without Spin Orbit Coupling (SOC)?

There are some famous materials is determined as TI induced by SOC, like graphene and so on. But from some formula, for instance, Kane-Fu formula, they just need parities to get Z2 number. So I wonder if there is a known TI with weak soc.
15. ### A What is Mott Transition and its basic Priniciple?

Hello Everyone, I was really curious to know what really is Mott Transition and How it works. I searched for hours but couldn't find any helpful answer. Somewhere it was suggested that it is a bridge between Quantum and Classical Mechanics and it is due to electron interaction where electron...
16. ### Can a neutral insulator be attracted to a charged object?

Homework Statement Hi all. I'm a teacher and one of my students asked me a question I couldn't answer today. It's a multiple choice question: A neutral object is attracted to an electrically charged rod. The two are not touching. The neutral object: A. is a conductor B. is an insulator C...
17. ### Electric potential outside an insulator in a uniform field

Homework Statement An Ohmic material with some conductivity has a uniform current density J initially. Let's say the current is flowing in the direction of the z-axis. A small insulating sphere with radius R is brought inside the material. Find the potential outside the sphere. Homework...
18. ### B What makes a material an insulator?

(This is a two part question.) Ok, so I have been trying to find what property of a material determines if it is a good conductor or not. I'm hoping to go beyond just if it can conduct electricity or not. One of the explanations I have found is the length of the band gap. Is this right or...
19. ### Can there be an electric field inside an insulator?

Just as the title asks, I wonder if there can be any electric field inside an insulator when a point change is placed near it. If so, why?
20. ### How an Electric Field is affected by an Insulator

I looked through this forum post for an answer to my problem. It gave me enough insight to try and come to some conclusions but I'm still confused on some parts here and there about how I got my final answer. 1. Homework Statement A uniformly charged, straight filament 7.70 m in length has a...
21. ### Charged insulator touches a conductor

Ques : If a neutral metal sphere placed on an insulating stand is touched by a charged plastic rod , does the metal sphere acquire any charge ? I think that by simply touching the sphere by insulating rod , the metal should not acquire any charge as the charges on the rod are immobile unlike a...
22. ### Charged insulator in contact with conductor

Homework Statement Homework EquationsThe Attempt at a Solution [/B] This is a quite a fundamental question in electrostatics and I felt pretty embarrassed getting it wrong .I thought correct option was d) . Could someone help me understand how conductor could acquire charge as charges...
23. ### A Black hole as topological insulator

Hi, is anyone familiar with topological insulator? I read an interesting paper: http://arxiv.org/abs/1703.09365, Black hole as topological insulator Abstract: Black holes are extraordinary massive objects which can be described classically by general relativity, and topological insulators are...
24. ### What is the charge density on the insulator?

Homework Statement Insulator has a 3 cm radius and is a sphere. It has a total charge of -4.2 uC. I need to find the charge density of the insulator. Homework Equations sigma = total charge / volume... I think? The Attempt at a Solution After using the above equation, I got -3.714E-8 C/m I...
25. ### Potential of Concentric Cylindrical Insulator and Conducting

Homework Statement An infinitely long solid insulating cylinder of radius a = 4.3 cm is positioned with its symmetry axis along the z-axis as shown. The cylinder is uniformly charged with a charge density ρ = 28 μC/m3. Concentric with the cylinder is a cylindrical conducting shell of inner...
26. ### B Exploring the Paradoxical Properties of Samarium Hexaboride

I'm no physicist, but I found this material to be interesting. Samarium Hexaboride is a crystal that exhibits conductive properties at room temperature and insulating properties when cooled to below minus 223 degrees Celsius. A layman's article...
27. ### B Time reversal symmetry in topological insulator

Hi all My question: I have read: Topological Insulators: Dirac Equation in Condensed Matters But also I have read: Observation of a Discrete Time Crystal Is it different situations ?
28. ### Quantum obstacle course changes material from superconductor to insulator

"a material to conduct an electrical current with zero resistance" ? Is this not ohm's law to a logical extreme?, or am I missing something?
29. ### Surface plasmon polaritons at metal / insulator interfaces

Homework Statement Consider the metal-vacuum interface located at z = 0,the metal filling the entire half-space z ≥ 0, vacuum filling (!?) the half-space z < 0. The dielectric function in the metal in the long-wavelength limit is given by: where ε0 is the vacuum permittivity. In the metal a...
30. ### The Permittivity of Insulators

I just have a few conceptual questions: Is it as difficult to remove electrons from an insulator as it is to add to it? I understand insulators have a lower permittivity than conductors, and that they still allow charges to build upon the surface. However, I read that when you rub an insulator...
31. ### Spherical Shell using Gauss' Law

Homework Statement An insulator is in the shape of a spherical shell. The insulator is defined by an inner radius a = 4 cm and an outer radius b = 6 cm and carries a total charge of Q = + 9 C (1 C = 10-6 C). You may assume that the charge is distributed uniformly throughout the volume of the...
32. ### Why isn't rubber a better thermal insulator than styrofoam?

I haven't studied materials in depth, but I would assume that something like rubber would make a good insulator because of its bounciness. The molecules of a substance contained in a rubber container would collide with the walls of the container in a very elastic collision, and the kinetic...
33. ### A Trapping the sun in a perfect insulator

So this is kind of a crazy hypothetical, but what would happen if you surrounded the sun in an invulnerable, perfectly insulating sphere that prevents anything from leaving. I imagine that as the sun heats up, the rate of fusion increases and the life time of the sun decreases. But that's about...
34. ### Conductor vs Insulator Effects

If a negatively charged Styrofoam plate is brought towards pieces of paper placed on an insulator (ex. a piece of paper), attraction occurs. Repulsion occurs if pieces of aluminum foil, which is a conductor, are placed on an insulator. What would occur if the pieces of paper and aluminum foil...
35. ### High temperature insulating material for new engine concept

In the past, reciprocating engine platforms have prevented the use of thermal insulating materials like ceramics due to, among other reasons, abrasion and vibration. One of the problems in the past has been the movement of the piston and piston rings over the cylinder wall where the insulating...
36. ### Insulator density and thermal conductivity

How does insulator's density affect its thermal conductivity? For example, considering such insulators as rock wool, It seems that the thermal conductivity should increase with an increase in density (due to elimination of 'air pockets'). However, experimental results, in many cases, look more...
37. ### Embedding Charge in an Insulator

I have been really fascinated with the dielectric breakdown artwork by Bert Hickman seen here. He is using a 5MeV accelerator to embed electrons in acrylic. He then discharges them to create beautiful fractal patterns. I emailed him last year asking how to calculate the penetration depth of...
38. ### Semiconductor and insulator

I am interested in simply simulating in MATLAB or an open source software, the following qualitative explanation of the band theory. I want to show to an undergraduate course maybe a simple applet with the difference between semiconductor (Si) and insulator (Diamond for example) . do you have...
39. ### Is there an easy review about topological insulator?

Hello. Is there a review paper about topological insulator which is written for non-physics major people? If it will be helpful, I know classical physics, basics about band theory and little bit of modern physics, and have just finished learning quantum mechanics (with a book written by...
40. ### Insulator in an electric field

Homework Statement Homework EquationsThe Attempt at a Solution [/B] I suppose the answers are A and C .A depicting the eletric field lines and C equipotential lines . Is it correct ? I arrived at the answer by eliminating choices B and D . Since electric field lines cannot intersect...
41. ### Topological Insulator: A Zero-Gap Material With SOC?

Hi every one, I face with a question on my works, As you know there in many articles Physicist introduce a material that has zero gap without spin-orbit coupling (SOC). By applying the SOC, a relatively small gap (0.1 eV) is opened and it becomes topological insulator. My question, Is that...
42. ### Effect of TRS potential on Topological insulator (QSH)

Hi every body, I faced a paradox. The topological insulator is robust against a potential that does not breaks the TRS. But in the original work of Kane-Mele (PRL 95, 146802), the "staggered sublattice potential" that does not breaks the TRS,, makes zigzag ribbon trivial insulator (figure 1 in...
43. ### High power bushing (HV power line insulator shapes)

Hello, I would like to understand why "bushings" that are used as insulation for high power electric cables in transformers, and which are often made out of porcelain or glass, I would like to understand why they have this form of "skirts" ? Why aren't they just as a simple cylinder?
44. ### Better Thermal Insulator for Glass - Neoprene or Silicone?

I am looking to improve the thermal insulation on one of my favorite glass mugs. I am choosing between a silicone glove or a neoprene wrap. What is the difference between a silicone baking mat and silicone rubber? Does silicone or neoprene have better thermal insulation?
45. ### Solid Insulator Sphere Inside Hollow Sphere Conductor

Homework Statement I was looking for some practice problems in my textbook and found this problem that I was just a little stuck on. I drew the diagram from my textbook with the givens of the problem. Homework Equations ∲E*dA = Q (inside) / ɛ0 The Attempt at a Solution For r less...
46. ### Why does wood move when charged with the same rod as an aluminium can?

So I just started Physics 2 Electricity and Magnetism and I'm already scared for my life. The professor first did a demonstration where he charged up a Teflon rod on some sort of cloth and moved an aluminium can with the rod. I understand how that happens. The can is a metal and conductor so the...
47. ### Can a Dragon Direct Lightning If It Can't Create an Opposite Charge?

Okay- first off, I know enough science to sound like an idiot, so please be gentle :-) Now, IF you had a dragon that generated an electrical charge, it wouldn't be able to direct it, lightning-style, without being able to generate an opposite charge at it's target- right? So in essence, to shot...
48. ### Metal insulator transition and percolation

Hello, For the past 2 days I've been looking for a resource discussing the metal insulator transition using percolation theory. (The next part treats the Anderson and Mott models) I'm studying for a course of solid state physics where this is mentioned/summarized. The problem is that the...
49. ### Self-learning topological insulator

I would like to learn topological insulator. But what kind of reference should I look for. I just have some basic solid state physics knowledge. I know there are lots of Hall Effects (e.g. spin hall effect, quantum hall effect ...etc). and I just know the idea of them, but not the math
50. ### Potential of concentric cylindrical insulator & conducting shell. Stuck on 2nd question

An infinitely long solid insulating cylinder of radius a = 5.2 cm is positioned with its symmetry axis along the z-axis as shown. The cylinder is uniformly charged with a charge density ρ = 23 μC/m3. Concentric with the cylinder is a cylindrical conducting shell of inner radius b = 14.2 cm, and...