current

Origin: curant, present participle of courre 'to run', from Latin currere]

Current may refer to:

• Current (fluid), the flow of a liquid or a gas
  • Air current, a flow of air
  • Ocean current, a current in the ocean
    • Rip current, a kind of water current
  • Current (stream), currents in rivers and streams
  • Convection [对流] current, flow caused by unstable density variation due to temperature differences
• Current (mathematics), geometrical current in differential topology
• Electric current, a flow of electric charge through a medium
• Probability current, in quantum mechanics

A rip current, often simply called a rip (or misleadingly a rip tide), is a specific kind of water current that can occur near beaches with breaking waves. A rip is a strong, localized, and narrow current of water which moves directly away from the shore, cutting through the lines of breaking waves like a river running out to sea. A rip current is strongest and fastest nearest the surface of the water.

An electric current is a stream of charged particles, such as electrons or ions, moving through an electrical conductor or space. It is measured as the net rate of flow of electric charge past a region. The moving particles are called charge carriers, which may be one of several types of particles, depending on the conductor. In electric circuits the charge carriers are often electrons moving through a wire. In semiconductors they can be electrons or holes. In an electrolyte the charge carriers are ions, while in plasma, an ionized gas, electric current is formed by both electrons and ions.

The SI unit of electric current is the ampere, or amp, which is the flow of electric charge across a surface at the rate of one coulomb per second. The ampere (symbol: A) is an SI base unit Electric current is measured using a device called an ammeter.

Electric currents create magnetic fields, which are used in motors, generators, inductors, and transformers. In ordinary conductors, they cause Joule heating, which creates light in incandescent light bulbs. Time-varying currents emit electromagnetic waves, which are used in telecommunications to broadcast information.

In quantum mechanics, the probability current (sometimes called probability flux) is a mathematical quantity describing the flow of probability. Specifically, if one thinks of probability as a heterogeneous fluid, then the probability current is the rate of flow of this fluid. It is a real [实数] vector that changes with space and time. Probability currents are analogous to mass currents in hydrodynamics and electric currents in electromagnetism. As in those fields, the probability current is related to the probability density function via a continuity equation. The probability current is invariant under gauge transformation.

• 连续性方程是质量守恒定律在流体力学中的具体表述形式。

六级/考研单词: fluid, liquid, rip, differentiate, mathematics, geometry, medium, mechanic, seldom, mislead, tide, shore, particle, electron, conduct, carrier, motor, bulb, emit, telecommunications, podcast, equate, gauge