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Speaker 1: Welcome to brain Stuff from house stuff works dot com,

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Speaker 1: where smart happens. I am Marshall Brand with today's question,

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Speaker 1: what is superconductivity. Super Conductivity is something that scientists have

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Speaker 1: known about for decades. In several medals, if you cool

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Speaker 1: them down to near zero degrees kelvin, they will become

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Speaker 1: super conducting, meaning that they will lose their electrical resistance.

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Speaker 1: Zero degrees kelvin is the same as minus four nine

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Speaker 1: degrees fahrenheit or minus two seventy degrees celsius. It's about

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Speaker 1: as cold as anything can get, and if you have

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Speaker 1: liquid helium, it gets down near zero degrees kelvin. So

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Speaker 1: if you immerse a metal like zinc or aluminum, or

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Speaker 1: tin or mercury in liquid helium, they will become superconductors.

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Speaker 1: The temperature at which a material loses its electrical resistance

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Speaker 1: is called the critical temperature, and recently scientists have found

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Speaker 1: several ceramic materials which have much higher critical temperatures, like

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Speaker 1: the temperature of liquid nitrogen. This is important because liquid

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Speaker 1: helium is really expensive, while liquid nitrogen has a cost

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Speaker 1: that's roughly equal to the cost of milk. Superconductivity is

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Speaker 1: a big deal because electricity is an important part of

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Speaker 1: our lives. Because superconductive materials have no electrical resistance, meaning

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Speaker 1: electrons can travel through them freely. They can carry large

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Speaker 1: amounts of electrical current for long periods of time without

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Speaker 1: losing energy is heat. Superconducting loops of wire have been

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Speaker 1: shown to carry electrical currents for several years with no

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Speaker 1: measurable loss. This property could be a big deal for

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Speaker 1: electrical power transmission if trans mission lines can be made

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Speaker 1: of superconducting ceramics, and it could also have a big

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Speaker 1: effect on things like storage of electricity, because in theory,

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Speaker 1: you could store electricity and a superconducting loop and hold

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Speaker 1: it there for years. Another property of a superconductor is

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Speaker 1: that once the transition from the normal state to the

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Speaker 1: superconducting state occurs, external magnetic fields can't penetrate it. This

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Speaker 1: effect is called the Meisner effect and it has implications

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Speaker 1: for making high speed magnetically levitated trains. It also has

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Speaker 1: implications for making powerful, small superconducting magnets for magnetic resonant imaging.

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Speaker 1: So this brings up an obvious question, how do electrons

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Speaker 1: travel through superconductors with no electrical resistance. Let's take a

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Speaker 1: look at this a little more closely. The atomic structure

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Speaker 1: of most metals is a lattice structure, much like a

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Speaker 1: windows screen, in which the intersection of each set of

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Speaker 1: perpendicular lines is an atom. Metals hold onto their electrons

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Speaker 1: quite loosely, so these particles can move freely through this lattice.

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Speaker 1: This is why metals conduct heat and electricity very well

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Speaker 1: to begin with. As electrons move through a typical metal

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Speaker 1: in the normal state, they collide with atoms and lose

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Speaker 1: energy in the form of heat. In a superconductor, the

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Speaker 1: electrons travel in pairs and move quickly between the atoms

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Speaker 1: with a lot less energy loss. As a negatively charged

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Speaker 1: electron moves through the space between two rows of positively

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Speaker 1: charged atoms, like the wires in a windows screen, it

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Speaker 1: pulls inward on the atoms. This distortion attracts a second

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Speaker 1: electron to move in behind it. This second electron encounters

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Speaker 1: less resistance, much like a passenger car following a truck

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Speaker 1: on the freeway encounters less air resistance. The two electrons

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Speaker 1: form a weak attraction, travel together in a pair, and

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Speaker 1: encounter less resistance overall. In a superconductor, electron pairs are

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Speaker 1: constantly forming, breaking and reforming. But the overall effect is

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Speaker 1: that electrons flow with little or no resistance. The low

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Speaker 1: temperature makes it easier for the electrons to pair up.

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Speaker 1: One final property of superconductors is that when two of

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Speaker 1: them are joined by a thin insulating layer, it's easier

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Speaker 1: for the electron pairs to pass from one superconductor to

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Speaker 1: another without resistance. This is known as the DC Josephson effect,

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Speaker 1: and you may have heard of the Josephson junction. This

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Speaker 1: effect has implications for super fast electrical switches that can

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Speaker 1: be used to make small, high speed computers. The future

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Speaker 1: of superconductivity research is defying materials that can become superconductors

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Speaker 1: at room temperature. Once this happens, the whole world of electronics, power,

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Speaker 1: and transportation could be completely revolutionized. For more on this

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Speaker 1: and thousands of other topics, visit how stuffworks dot com

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