WEBVTT - What is superconductivity?

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<v Speaker 1>Welcome to brain Stuff from house stuff works dot com,

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

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<v Speaker 1>what is superconductivity. Super Conductivity is something that scientists have

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<v Speaker 1>known about for decades. In several medals, if you cool

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<v Speaker 1>them down to near zero degrees kelvin, they will become

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<v Speaker 1>super conducting, meaning that they will lose their electrical resistance.

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<v Speaker 1>Zero degrees kelvin is the same as minus four nine

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<v Speaker 1>degrees fahrenheit or minus two seventy degrees celsius. It's about

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<v Speaker 1>as cold as anything can get, and if you have

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<v Speaker 1>liquid helium, it gets down near zero degrees kelvin. So

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<v Speaker 1>if you immerse a metal like zinc or aluminum, or

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<v Speaker 1>tin or mercury in liquid helium, they will become superconductors.

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<v Speaker 1>The temperature at which a material loses its electrical resistance

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<v Speaker 1>is called the critical temperature, and recently scientists have found

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<v Speaker 1>several ceramic materials which have much higher critical temperatures, like

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<v Speaker 1>the temperature of liquid nitrogen. This is important because liquid

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<v Speaker 1>helium is really expensive, while liquid nitrogen has a cost

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<v Speaker 1>that's roughly equal to the cost of milk. Superconductivity is

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<v Speaker 1>a big deal because electricity is an important part of

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<v Speaker 1>our lives. Because superconductive materials have no electrical resistance, meaning

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<v Speaker 1>electrons can travel through them freely. They can carry large

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<v Speaker 1>amounts of electrical current for long periods of time without

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<v Speaker 1>losing energy is heat. Superconducting loops of wire have been

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<v Speaker 1>shown to carry electrical currents for several years with no

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<v Speaker 1>measurable loss. This property could be a big deal for

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<v Speaker 1>electrical power transmission if trans mission lines can be made

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<v Speaker 1>of superconducting ceramics, and it could also have a big

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<v Speaker 1>effect on things like storage of electricity, because in theory,

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<v Speaker 1>you could store electricity and a superconducting loop and hold

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<v Speaker 1>it there for years. Another property of a superconductor is

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<v Speaker 1>that once the transition from the normal state to the

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

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<v Speaker 1>effect is called the Meisner effect and it has implications

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<v Speaker 1>for making high speed magnetically levitated trains. It also has

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<v Speaker 1>implications for making powerful, small superconducting magnets for magnetic resonant imaging.

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<v Speaker 1>So this brings up an obvious question, how do electrons

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<v Speaker 1>travel through superconductors with no electrical resistance. Let's take a

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<v Speaker 1>look at this a little more closely. The atomic structure

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<v Speaker 1>of most metals is a lattice structure, much like a

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<v Speaker 1>windows screen, in which the intersection of each set of

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<v Speaker 1>perpendicular lines is an atom. Metals hold onto their electrons

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<v Speaker 1>quite loosely, so these particles can move freely through this lattice.

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<v Speaker 1>This is why metals conduct heat and electricity very well

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<v Speaker 1>to begin with. As electrons move through a typical metal

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<v Speaker 1>in the normal state, they collide with atoms and lose

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<v Speaker 1>energy in the form of heat. In a superconductor, the

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<v Speaker 1>electrons travel in pairs and move quickly between the atoms

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<v Speaker 1>with a lot less energy loss. As a negatively charged

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<v Speaker 1>electron moves through the space between two rows of positively

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<v Speaker 1>charged atoms, like the wires in a windows screen, it

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<v Speaker 1>pulls inward on the atoms. This distortion attracts a second

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<v Speaker 1>electron to move in behind it. This second electron encounters

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<v Speaker 1>less resistance, much like a passenger car following a truck

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<v Speaker 1>on the freeway encounters less air resistance. The two electrons

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<v Speaker 1>form a weak attraction, travel together in a pair, and

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<v Speaker 1>encounter less resistance overall. In a superconductor, electron pairs are

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<v Speaker 1>constantly forming, breaking and reforming. But the overall effect is

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<v Speaker 1>that electrons flow with little or no resistance. The low

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<v Speaker 1>temperature makes it easier for the electrons to pair up.

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<v Speaker 1>One final property of superconductors is that when two of

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<v Speaker 1>them are joined by a thin insulating layer, it's easier

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<v Speaker 1>for the electron pairs to pass from one superconductor to

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<v Speaker 1>another without resistance. This is known as the DC Josephson effect,

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<v Speaker 1>and you may have heard of the Josephson junction. This

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<v Speaker 1>effect has implications for super fast electrical switches that can

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<v Speaker 1>be used to make small, high speed computers. The future

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<v Speaker 1>of superconductivity research is defying materials that can become superconductors

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

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<v Speaker 1>and transportation could be completely revolutionized. For more on this

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<v Speaker 1>and thousands of other topics, visit how stuffworks dot com

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