Surface Definition and 1000 Threads

Homework Statement (From Griffiths problem 2.26) : A conical surface (an empty ice-cream cone) carries a uniform surface charge σ. The height of the cone is h, and the radius of the top is R. Find the potential difference between points a (the vertex) and b (the center of the top).Homework...

If I push an object such as a cylinder of wood along a flat table (flat face of cylinder in contact with the table) through it's center of mass, the friction or energy required is not dependent of the surface area the block makes with the table, Friction = μ N, correct? And the energy required =...

Homework Statement A mass m that is free to move on a horizontal frictionless surface, is attached to one end of a massless string that wraps partially around a frictionless vertical pole of radius r, as in the Figure below.You are holding onto the other end. At t=0 the mass has speed V0 in the...

I'm working on this: When I consider a disc with radius ##a## and total charge ##Q## uniformly distributed (placed in the XY plane and centered at the origin) and determine the volume charge density in cylindrical coordinates, I have assumed is of the form ##\rho=A \delta (z) U(R-r)##, (##U## is...

in a P-N junction diode, in an equilibrium state, a depletion layer forms in the surface of contact of N type and P type. But the problem is, this layer is formed by diffusion of electron to a lower electron density zone. Why does it always have to form right in the contactt surface? when...

I am currently reading Young & Freedmans textbook on physics as part of a university course, and I've noticed that they repeatedly represent surface integrals (which are double integrals) as single integrals. For instance, they symbolically represent the magnetic flux through a surface as: \int...

Homework Statement Homework EquationsThe Attempt at a Solution I have the full solution, the first part being: I don't understand how they came up with the expression for Vab. I know usually ΔV=-∫E dl, but I'm not sure how they found their expression. Can someone explain? Thanks.

Is there any entropic gain when the surface of a liquid is minimised? Per example, molecules "enjoy" maximum entropy when they are at the interior. Is this valid?

Homework Statement Consider a planar liquid-gas interface and a solid sphere partially immersed in liquid. A fraction of the solid surface area is wet by the liquid, call it ##A_{sl}##. The complement of the solid’s area is ‘wet’ by the gas, say ##A_{sg}##. There is also an area of contact...

While going through the derivation to find the surface tension of liquid i came with the formula which says that the surface tension is directly proportional to radius of the capillary so does that imply if we use a capillary with a greater radius so the same will give the different value of...

Homework Statement Calculate the surface charge density induced by a point source above an infinite conducting plane, with 0 potential. Homework Equations ##E=-\nabla V## ##V=\frac{q}{4\pi \epsilon_0 r}## The Attempt at a Solution I used the method of image charges and I calculated the...

Is there any limit for which we can approximately write the surface area of a prolate ellipsoid to be 4piA*B comparing with the spherical 4piR*R??

Hello! I am a bit confused about calculating the induced surface charge density on an infinite conducting plane, with 0 potential, in the presence of a charge, q, a distance d above it. Assuming that the plane is in xy plane and the charge in positive z region, in the book they use the method of...

$ \tiny{231.14.88}\\$ $\textsf{Identify and briefly describe the surface of the equation}\\$ \begin{align*} S_{88}&=\frac{-x^2-y^2+z^2}{9+6x-8y}=26 \end{align*} $\textit{this had no template example but on}\\$ $\textit{ W|A it looked like a torus?}\\$ $\textit{where is a good online 3d graphing...

I have never heard of a way to investigate this mathematically but I'm sure there is. How would you describe the surface area or volume of some 3-D surface formed by moving an enclosed area along a curved axis a certain distance? You could easily describe a torus by taking a circle and forming...

Homework Statement The electric field strength just above one face of a copper penny is 2230 N/C. What is the surface charge density on this face of the penny? Homework Equations Electric field of an infinite plane of charge = η/(2*ε0) The Attempt at a Solution I used the above equation, and...

Homework Statement Let n be the unit outward normal of a spherical surface of Radius R, let the surface of the sphere be denoted by S. Evalute Surface integral of nndS Homework EquationsThe Attempt at a Solution I have evaluated the surface integral of ndS and found it to be 0. but am not...

Eventually the Sun will go through its phases and cool down. Is it possible to calculate how long it will take for the surface to cool to 75 degrees Fahrenheit?

Homework Statement Problem: A 12.0-kg block is pushed to the left across a rough horizontal surface by a force that is angled 30.0◦ below the horizontal. The magnitude of the force is 75.0 N and the acceleration of the block as it is pushed is 3.20 m/s^2 . What angle does the force exerted on...

Hi, My textbook has a multiple choice question about which stellar object has the highest surface temperature and the answer was a white dwarf. However, one of the options was a neutron star. Neutron stars are much denser and have been crushed by gravity even more plus they are rotating at...

Homework Statement A metal sphere of radius a is surrounded by a metal shell of inner radius b and outer radius R, as shown in the diagram below. The flux through a spherical Gaussian surface located between a and b is 1.20Q/εo and the flux through a spherical Gaussian surface just outside R is...

Homework Statement Homework Equations E=σ/(2Eo) σ=2Eoma/e a=Δv/Δt The Attempt at a Solution So doing my best to read the velocity over time graph I came up with Δv/Δt=(-2E5m/s)/(10E-12s)=-2E17 m/s/s σ=2Eoma/e =2(8.99E-9C)(9.109E-31kg)(-2E17m/s/s)/(1.6022E-19) =-0.020444 C/m^2 but by the...

Homework Statement A vector field $\vec F$ is defined in cylindrical polar coordinates $\rho , \theta , z$ by $\vec F = F_0(\frac{xcos (\lambda z)}{a}\hat i \ + \frac{ycos(\lambda z)}{a}\hat j \ + sin(\lambda z)\hat k) \ \equiv \frac{F_0 \rho}{a}cos(\lambda z)\hat \rho \ + F_0sin(\lambda...

I found it very interesting to see that surface charge and the Poynting vector are being used to describe how a simple DC circuit actually works. Chabay and Sherwood have made an outstanding contribution to physics and engineering in their texts and papers. Of course others jump on the...

Homework Statement Calculate surface temp of heat exchanger when it's heating the room with the known power of P. Room temperature T is also known, as is the heater surface area A. ε ≈ 1. Homework Equations P = εσAT^4 is what I've been trying to use. The Attempt at a Solution I've been...

I will use an example: -The surface is given by the intersection of the plane: y+z=2 -And the infinite cilinder: x2+y2<=1 We want to parametrize this surface, it could be done easily with: x=r cosθ y=r sin θ z=2 - r cos θ Then this surface could be written using vector notation: S= r...

Homework Statement There is a disk with mass 50 grams put on a slippy surface (no friction!). Its radius is 5 cm. Mass of the weight is 20 grams. At the beginning there is no motion. How far does the center of mass of the disk move in 10 seconds? (answer: 91 m) How many turns does the disk in...

Hi guys, First of all, thank you for your help. I am new in Ansys and Fluent (less than a month), hoping to learn. I am trying to model a simple and single surface reaction CH4 (g) -> C(s) + 2H2 (g) on a "CVD reactor" to grow C(s) (graphene, or graphite). The inlets are gases inyections of...

Homework Statement Sketch the surface of a paraboloid z=9-x2 -92 in 3-dimensional xyz-space Homework Equations I assume partial derivatives are involved in some manner The Attempt at a Solution [/B] I attempted to solve by making each variable equal to zero... That didn't work xD. I would...

Let V be the region bounded by the hemisphere z=1-sqrt(1-x^2-y^2) and the plane z=1, and let S be the surface enclosing V. consider the vector field $F= x(z-1)\hat{\imath}+y(z-1)\hat{\jmath}-xy\hat{k}$.

Homework Statement The two blocks ##(m=16 kg)## and ##(M=88 kg )## , are not attached to each other.The coefficient of static friction between the blocks is ##μ=0.33##, but the surface beneath the larger block is frictionless.What is the minimum magnitude of the horizontal...

Homework Statement A 1 500kg satellite is in orbit 250km above Earth's surface. What minimum additional energy is needed to place this satellite in a new stable orbit 800km above Earth's surface? Homework Equations W = delta Ep = -GMm(1/r2-1/r1) Ep = -GMm/r Ek = GMm/2r or 1/2mv^2 The...

Homework Statement Will a frictionless body placed on the Earth move, and if so, describe it's path and acceleration. Homework Equations I was given no equations, but I believe that coriolis and centripetal forces would act on the body.The Attempt at a Solution I assume that we have to assume...

Given that 1.34Tbit of information can fit on a square inch of average hard drive surface, how many 400 KB files could be written on a square millimeter? I did the math and came up with about 634. This seems unbelievably high and I wonder if someone would have time to check it. I kind of need...

Homework Statement A hollow stirrer that has a diameter of 2.0 mm is inserted into a cup of water at 20∘C. The surface tension of water at that temperature is γ(surface tension) = 7.28×10−2 N/m. What is the mass of the water supported by the surface tension in the stirrer? Given: d=2 mm...

Charles Link submitted a new PF Insights post Permanent Magnets Explained by Magnetic Surface Currents Continue reading the Original PF Insights Post.

Homework Statement Consider the cardioid given by the equations: ##x = a(2\cos{t} - \cos{2t})## ##y = a(2\sin{t} - \sin{2t})## I have to find the surface that the cardioid circumscribes, however, I don't know what limits for ##t## I have to take to integrate over. How can I know that, as I...

Homework Statement A student looks at the sunlight reflected off a puddle of water. She puts a polarising (Polaroid) filter in front of her eye. As she rotates the filter the puddle appears darker then lighter. Explain this observation Homework EquationsThe Attempt at a Solution Here's my...

Homework Statement Is the solution provided by the author wrong ? Stokes theorem is used to calculate the line integral of vector filed , am i right ? Homework EquationsThe Attempt at a Solution To find the surface integral of many different planes in a solid , we need to use Gauss theorem ...

https://web.mst.edu/~numbere/CP/CHAPTER%203.htm I have trouble understanding why the length used in 3.1.1 is pir^2. My notes don't explain what length we use either.

So if I drop an apple, we can consider the ground accelerating upwards and the apple still. And the radius of the Earth doesn't change due to space time being curved. I'm having a hard time conceptualizing this. Is it analogous to a classically orbiting object? Classically, under simplfying...

Hi everyone, While studying surface tension I came across a(numerical example) problem which asks to find the force required to pull a circular glass plate of some given radius from the surface of water(assume plane of plate on water surface). Value of surface tension of water is also given in...

If you increase surface tension, the molecules at the surface are more strongly pulled into the center of mass due to the stronger attractive molecular forces. -Why is it that when surface tension increases in a liquid, its surface decreases in area, but its volume does NOT change? (Volume...

Homework Statement Hi, Infinitely far away from a mass-->gravitational potential is zero. As get closer-->becomes negative. At surface-->it is the smallest value of r, i.e. the radius of the mass, hence the most negative value for gravitational potential. But as you go below surface of Earth...

Homework Statement A fish watcher at point P watches a fish through a glass wall of a fish tank. The watcher is level with the fish; the index of refraction of the glass is 8/5, and that of the water is 4/3. The distances are d1=8.0 cm, d2=3.0 cm, and d3=6.8 cm (a) To the fish, how far away...

Homework Statement We are given a Banana, and asked to find the volume and surface area of the function, using calculus. So far, we have learned elementary calculus (derivatives, limits, and integrals) as well as volumes of revolutions. We traced the banana on graph paper, plotted points on the...

I am doing surface failure analysis for a ball bearing SKF 6025, , as an exercise, It has been used in the washing machine tub, after some time a noise has been reported and it is no longer rotating. When i got it I opened the seal and captured the attached photo. I had a feeling that it suffers...

Homework Statement Calculate ##\iint { y+{ z }^{ 2 }ds } ## where the surface is the upper part of a hemisphere with radius a centered at the origin with ##x\ge 0## Homework Equations Parameterizations: ##\sigma =\left< asin\phi cos\theta ,asin\phi sin\theta ,acos\phi \right> ,0\le \phi \le...

we interest one V-Sorb 2800 BET surface area analyzer, using physical adsorption principle to test particles surface area data, if anyone knows this analyzer principle?

Homework Statement A landing craft with mass 1.22×10^4 kg is in a circular orbit a distance 5.50×10^5 m above the surface of a planet. The period of the orbit is 5100 s . The astronauts in the lander measure the diameter of the planet to be 9.50×10^6 m . The lander sets down at the north pole...