# What is Surface density: Definition and 18 Discussions

The area density (also known as areal density, surface density, superficial density, areic density, mass thickness, column density, or density thickness) of a two-dimensional object is calculated as the mass per unit area. The SI derived unit is: kilogram per square metre (kg·m−2). In the paper and fabric industries, it is called grammage and is expressed in grams per square meter (gsm); for paper in particular, it may be expressed as pounds per ream of standard sizes ("basis ream").

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1. ### Surface density of the charges induced on the bases of the cylinder

The correct answer to this problem is: ##\sigma = \varepsilon_0E\frac{\varepsilon-1}{\varepsilon}## Here is my attempt to solve it, please tell me what is my mistake? ##E_{in} = E_{out} - E_{ind}## ##E_{ind} = E_{out} - E_{in}## ##E_{in} = \frac{E_{out}}{\varepsilon}## ##E_{ind} = E_{out} -...
2. ### Surface density of stars in a Galaxy

a.) The scale length of the disk is the length over which the surface density of stars decreases by a factor of e. In this case, the surface density decreases by a factor of 10 over a distance of 9 kpc, so the scale length is 9 kpc. The surface density of stars at a radius of r from the center...
3. ### Connection between Pressure, Surface Density and Height?

[Mentors' note: moved from technical forums so no template] Hi All, Working on a lab write-up, and I need background equations to support the reasoning for my experiment. To outline briefly, two-part experiment, first part was finding the ideal pressure for a basketball, where I inflated it...
4. ### Volume density vs Surface density of charge distribution

This doubt is confusing to me. I know it's something to do with conductors and insulators, but cannot explain. Conductors have mobile/free electrons unlike insulators. Having free electrons doesn't seem to explain this difference of charge distributions.
5. ### B How to find the surface density for a given linear density

Given a square with a linear mass density of: λ(x) = a * x (see image below where black is high density and white is low density) how would you deduce what the surface mass density is? I get confused for the following reason: To me it seems that the surface mass density should depend on x...
6. ### Electric Field of a solid sphere of non-uniform surface density

A solid sphere has surface charge density, Rho (r) Rho(r) = k 1 ( 0 < r < a) k2 x ( a < r < R) 2) Find the electric field in all region i.e 1) r < a and 2) a < r < R and 3 ) R < The attempted solution and the question with the diagram is attached below Could the answer be verified...
7. C

### Surface density on isolated conductors in space

Homework Statement There are n isolated condutoctors in space: Sum of charge of all conductors is positive. Show that surface density is postivie everywhere on at least one of conductors Homework Equations Using induction The Attempt at a Solution -It's clear that if we have one conductor...
8. ### How Do You Calculate the Surface Charge Density on a TV Screen?

Homework Statement You've probably noticed that TV screens and computer monitors have an annoying tendency to accumulate dust. Wanting to understand this better, you decide to model the situation as follows: you assume a small mote of dust might have an excess charge of 1 nC and a mass of 5...
9. ### Surface density diamond structure [1 1 1]

Homework Statement Calculate the surface density (planar density) of the Silicon diamond structure in the [1 0 0],[1 1 0],[1 1 1] planes. Given a = 5.431 A (latice constant) Hint: For the (111) plane, it should help you to think of the diamond lattice as two interpenetrating FCC lattices.2...
10. ### Mobility of 2D material, sigma=N*e*mu with N surface density

I have measured the conductivity of a 2D material. I want to use σ=N⋅e⋅μ to find the mobility μ=σ/(N⋅e). https://en.wikipedia.org/wiki/Electron_mobility#Relation_to_conductivity I have measured N using a spectroscopic/imaging technique to get a Surface Density with units [cm^-2]. Mobility...
11. ### E-field and charge density outside two coaxial cylinders

I am working on a problem of electrostatics, and I am having troubles in trying to figure out one part of it. 1. Homework Statement It consists of an inner solid cylinder of radius ##a## with a voltage ##V_A##, and an outer coaxial cylindrical shell of inner radius ##b## and outer radius ##c##...
12. ### Understanding Circumstellar Disks: Exploring Surface Density in 3D

Hi everyone, I'm trying to understand circumstellar disks. One term that keeps cropping up in this context is "surface density". The disks, though flattened, are still three-dimensional, so I'm confused about what "surface density" actually means. I can think of a couple of possibilities...
13. ### Mathematica 2D surface density plot in Mathematica

I am trying to plot the following function: \sigma(r, \phi) = \frac{3r^2}{\sqrt{1 - r^2}} e^{i(2 \phi - \omega t)} where \sigma is a surface density, r is radius, and \phi is azimuthal angle. It is supposed to yield a "bar shape" for a galactic disk, but I'm not sure how to go about...
14. ### Calculate Surface Density for SC, BCC & FCC Crystals

helppp Homework Statement Calculate the surface density of atoms on (111) and (110) planes for the following crystal structure. a) simple cubic, b) body-centered cubic, c)face-centered cubic. Assume the lattice constant is x. Homework Equations well, from reading my lecture notes...
15. ### Sun's Surface Density: Exploring the Mysteries of Our Star

I was looking at the http://antwrp.gsfc.nasa.gov/apod/ap060710.html" and marvelled how well-defined the Sun's surface is. I know about coronae and such, but still, it looks almost solid (though I know it's entirely gaseous). How well-defined is the surface? Does it go from transparent to...
16. ### Is Surface Density of Starlight Synonymous with Surface Brightness?

I have a problem that asks for the surface density of starlight at 8 kpc for a particular spiral galaxy. I have all the information to calculate surface brightness. Does "surface density of starlight" mean "surface brightness", or are these completely different things?
17. ### Can I get Surface Density from Volume Density?

I'm working on a vibration frequency problem involving a thin, circular aluminum membrane with a radius of 0.01m. I know the volume density of Al. How do I arrive at a surface density for this circular membrane -- especially since I'm not given the thickness (I'm told that frequencies...
18. D

### Geometry and Surface Density of Electric Charge

I have never seen an explicit formula to describe the relation between charge density and geometry (e.g. local curvatures) of the surface of a conductor. We all know that charge tends to accumulate at edges (high curvature) but can we be more quantitative? Hope someone else will find this...