# What is surface current: Definition and 22 Discussions

An ocean current is a continuous, directed movement of seawater generated by a number of forces acting upon the water, including wind, the Coriolis effect, breaking waves, cabbeling, and temperature and salinity differences. Depth contours, shoreline configurations, and interactions with other currents influence a current's direction and strength. Ocean currents are primarily horizontal water movements.
An ocean current flows for great distances and together they create the global conveyor belt, which plays a dominant role in determining the climate of many of Earth's regions. More specifically, ocean currents influence the temperature of the regions through which they travel. For example, warm currents traveling along more temperate coasts increase the temperature of the area by warming the sea breezes that blow over them. Perhaps the most striking example is the Gulf Stream, which makes northwest Europe much more temperate for its high latitude than other areas at the same latitude. Another example is Lima, Peru, whose cooler subtropical climate contrasts with that of its surrounding tropical latitudes because of the Humboldt Current. Ocean currents are patterns of water movement that influence climate zones and weather patterns around the world. They are primarily driven by winds and by seawater density, although many other factors – including the shape and configuration of the ocean basin they flow through – influence them. The two basic types of currents – surface and deep-water currents – help define the character and flow of ocean waters across the planet.

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1. G

### Surface current on a spherical superconductor

I need help with part b. My solution: Have I done it right?
2. ### Surface Current and Electric Field

Hi everyone! I'm pretty new in this forum, I found the topics here very relevant to my physics course. And here is my question: Given the following drawing, two infinite sheets (in y and z axis) of ideal conductive material. their thickness is infinitesimal (dx->0). The electric field is...
3. ### Bound Bulk Current Density and Surface Current Density

Hi there, I've worked through most of this question but I'm stuck on the final part, showing that total bulk current ##I_B## is equal and opposite to total surface current ##I_S##. I calculated ##\vec H## the normal way I would if I was looking for ##\vec B## in an infinitely long cylindrical...
4. ### Potential vector (A) of a disk with a surface current

Hi, I've been stuck for a long time with this exercise. I am not able to calculate the potential vector, since I do not know very well how to pose the itegral, or how to decompose the disk to facilitate the resolution of the problem. I know that because the potential vector must be parallel to...
5. ### Magnetic field of plane with thickness d with uniform surface current

I'm confused what's meant by a uniform surface current density since this plane has a thickness, It would need a current density distributed through its cross sections, I thought.Edit: I tried solving with proper LaTeX and all my steps, but it looked awful. For outside, I got B=µ_0jd/2. for...
6. ### Slowly oscillating surface current on a solenoid

Homework Statement From an original surface current ##\vec{K}=K\hat{\phi}## on a finite solenoid, I got ##\vec{B}=\mu_{0}Kf(z)\hat{k}##, for ##r<R##. Assuming that ##\vec{K}## now slowly oscillates in time such as: ##\vec{K(t)}=K_{0}\cos\left(\omega t\right)\hat{\phi}##, so that I still can use...
7. ### Relationship between line current & surface current density

Homework Statement In a configuration having axial symmetry about the z axis, a line current I flows in the −z direction along the z axis. This current is returned at the radii a and b, where there are uniform surface current densities Kza and Kzb , respectively. The current density is zero in...
8. ### Surface current density-logic and definition contradict

Okay, so in Griffith's introduction to electrodynamics, Griffith clearly defines surface current density as follows: "when charge flows over a surface, we describe it by the surface current density, K. Consider a 'ribbon' of infinitesimal width dL running parallel to the current flow. If the...
9. ### Cylinder carrying volume and surface current, H field

Homework Statement We have an infinite cylinder that, from radius 0 to a, has a volume current density ##\vec{J(r)}=J_{0}(r/a) \hat{z}## , then from a to 2a, it has a material with uniform linear magnetic permeability ##\mu=(3/2)\mu_0## , and at the surface, it has surface current...
10. ### Induced Surface Current in Conducting Plane, Dropped Charge

Homework Statement a) A charge q is released a distance d above a grounded infinite conducting plane. It's non relativistic velocity is v. Find the induced surface current density on the plane. b) Show that the above current density produces a vanishing magnetic force on the charge. Homework...
11. ### What does it mean for a charge to be uniformly distributed on a spherical shell?

Surface current density, K is defined as: K = σv where σ is surface charge density and v is velocity. Given a uniformly charged spherical shell with radius R, spinning at constant angular velocity ω, find the current. So, I start with this formula: dI = K dl dI = σ Rω dl and I placed the...
12. ### Vector Potential A: Discontinuity at the surface current

Homework Statement Prove Eqn. 1 (below) using Eqns. 2-4. [Suggestion: I'd set up Cartesian coordinates at the surface, with z perpendicular to the surface and x parallel to the current.] Homework Equations I used ϑ for partial derivatives. Eqn. 1: ϑAabove/ϑn - ϑAbelow/ϑn = -μ0K Eqn. 2: ∇ ⋅ A...
13. ### Confusion about bound surface current of a cube

If the magnetization vector is in the z direction, is the bound surface current of a cube always 0, since z cross z is 0, and x and -x cancels and y and -y cancels out?
14. ### Electric surface current on a PEC

Hello! When considering the boundary conditions for the electromagnetic field \mathbf{E}, \mathbf{H} on the surface of a Perfect Eletric Conductor we have: \mathbf{E} \times \mathbf{\hat{n}} = 0 \mathbf{J}_S = \mathbf{\hat{n}} \times \mathbf{H} the tangential electric field should vahish...
15. ### Em wave incident on a surface current

Consider an infinite sheet of surface current described by the surface current density , K=dI/dl, where dl is a length element perpendicular to the current. For this sheet, the magnetic field B=μK/2, above and below the sheet, independent of the distance from the sheet, where μ is for free...
16. ### Surface current density problem

Homework Statement A static surface current density Js(x,y) is confined to a narrow strip in the xy-plane In this static problem ∇ ⋅Js = 0. Show that the line-integral of Js along any cross-section of the strip will yield the same value for the total current I. (The direction of dl in these...
17. ### Surface current density problem

The surface current density, K, is defined as the the current through a unit width perpendicular to the flow. In particular: K = v\cdotσ where σ is the surface charge density. Now I have a little trouble understanding this formula intuitively. Can someone describe in pictures how it is...
18. ### Ocean Surface Current Visualization-worldwide

This visualization shows ocean surface currents around the world during the period from June 2005 through December 2007. The visualization does not include a narration or annotations; the goal was to use ocean flow data to create a simple, visceral experience. (beware, the downloadable...
19. ### Surface charges and surface current on conductors carrying steady currents

It is known that on a wire carrying steady current there are surface charges (and hence electric field outside the wire, but let's forget about it). This surface charges play an important role to maintain a uniform electric filed along the whole wire. There are only few geometries for which one...
20. ### Biot Savart Law with a surface current

Homework Statement There is a disc with radius R which has a uniformly-distributed total charge Q, rotating with a constant angular velocity w. (a) in a coordinate system arranged so that the disc lies in the xy plane with its center at the origin, and so that the angular momentum point in...
21. ### Time-dependent surface current density

We have an infinitely long solenoid of radius R along the z-axis. The solenoid is electrically neutral. The surface current density K is dependent in time, K(t)=Kocos(wt) Find the magnetic field B(s,t) produced for s<R (inside solenoid), s>R (outside solenoid), and the associated electric...
22. ### K, the idealized surface current density

K, the "idealized surface current density" Hey, I don't quite understand that guy, K. I have an exam on Sunday in E&M, I'm studying from Jackson. I haven't found any definition of 'K'. If anyone could give me a rigurous definition and an integral form, if there's any, I'd appreciate it...