# Self inductance of a superconductor

• greypilgrim
In summary, superconductors can create a hovering effect above or below magnets due to eddy currents on the surface cancelling out gravity. However, the internal currents cancel out, while external currents do not. This means that a superconducting coil can still conduct electricity, as self-inductance is dependent on magnetic coupling rather than resistance.
greypilgrim
Hi.

Superconductors can be made hover above or even below magnets. As far as I know, this can be interpreted as an extreme form of Lenz's law: Eddy currents on the surface of the superconductor create an opposing force that is able to cancel gravity since the currents aren't affected by resistance.

By that logic, shouldn't a superconducting coil have infinite self inductance and thereby be not conducting at all? Shouldn't turning on a current create a current of the same magnitude but opposite direction in neighboring loops so they exactly cancel?

It is the internal currents that cancel. The external currents do not.
There is no problem inducing a current to flow on the surface of a superconductor. The filaments of current that flow along the surface of a superconductor are coupled to each other. Likewise other parts of the same conductor that are further away couple less. Self-inductance is a function of the magnetic coupling of the conductor to all other parts of itself, quite independent of the resistance of the conductor.

## What is self inductance?

Self inductance is a property of a circuit element that describes its ability to generate an opposing electromotive force (EMF) in response to a change in current. It is typically denoted by the symbol L and is measured in henrys (H).

## What is a superconductor?

A superconductor is a material that exhibits zero electrical resistance and expels magnetic fields when cooled below a certain critical temperature. This allows for the flow of electrical current without any energy loss.

## How does a superconductor exhibit self inductance?

When a superconductor is subjected to a changing magnetic field, it generates a circulating current within itself that creates an opposing magnetic field. This self-generated magnetic field causes the superconductor to exhibit self inductance.

## What factors affect the self inductance of a superconductor?

The self inductance of a superconductor is primarily affected by its geometry, the strength of the magnetic field, and its critical current. It also depends on the type of superconductor, as different materials have different properties that can affect their self inductance.

## What are some practical applications of self inductance in superconductors?

Self inductance in superconductors is utilized in a variety of applications, such as in superconducting magnets for MRI machines and particle accelerators, in power transmission and storage systems, and in sensitive electronic devices that require stable and efficient electrical current flow.

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