Name: superconductor critical temperature
Uploaded: 2025-05-22T09:05:52.000Z
Duration: 1 min 24 s
Channel: JoVE

K12 Standards

Virginia  Standards of Learning

HIgh School

Physics

PH.9

PH.9.g

Superconductor

Un superconduttore è un materiale che offre una resistenza zero al flusso di elettroni con un efficiente trasferimento di energia elettrica e nessuna perdita di calore.
Nel 1911, Heike Kamerlingh Onnes osservò che la resistenza va a zero quando il mercurio si raffredda al di sotto di 4,2 Kelvin. Questa è nota come temperatura critica per il mercurio e il fenomeno è noto come superconduttività.
Quando la temperatura supera la temperatura critica, la resistenza cambia linearmente con essa.
Un altro aspetto del comportamento magnetico di un superconduttore si osserva quando un materiale superconduttore omogeneo viene posto in un campo magnetico uniforme esterno.
Quando la temperatura è maggiore della temperatura critica, il campo all'interno del materiale è uguale al campo magnetico uniforme esterno. Se è inferiore alla temperatura critica, il flusso magnetico viene espulso dal materiale e il campo al suo interno è zero. Questo fenomeno è noto come effetto Meissner.
La superconduttività di un materiale al di sotto della temperatura critica può essere eliminata applicando l'ampiezza minima del campo magnetico, nota come campo magnetico critico.

<ol>
	<li>OpenStax. (2019). Fisica universitaria Vol. 2. [Versione web], Pg 396 - 398. Estratto da <a href="https://openstax.org/books/university-physics-volume-2/pages/9-6-superconductors">https://openstax.org/books/university-physics-volume-2/pages/9-6-superconductors</a></li>
</ol>

superconduttore

Una sostanza che raggiunge la superconduttività, uno stato in cui i campi magnetici non possono penetrare e non c'è resistenza elettrica, è chiamata superconduttore. Nel 1911, Heike Kamerlingh Onnes dell'Università di Leida, un fisico olandese, osservò una relazione tra la temperatura e la resistenza dell'elemento mercurio. Il campione di mercurio fu quindi raffreddato nell'elio liquido per studiare la dipendenza lineare della resistenza dalla temperatura. Si osservò che, man mano che la temperatura diminuiva, la resistenza scendeva. Kamerlingh Onnes continuò a raffreddare ulteriormente il campione di mercurio e, quando la temperatura si avvicinava a 4,2 K, la resistenza scendeva bruscamente a zero. Questa è la temperatura critica per il mercurio, dove il campione di mercurio entra in una fase con resistenza zero assoluta, e questo fenomeno è noto come superconduttività. Nel caso dei conduttori, la resistenza non è uguale a zero ma è inferiore a 0,01 ohm. Esistono vari metodi per misurare resistenze molto piccole, come il metodo dei quattro punti, ma un ohmetro non è accettabile per testare la resistenza della superconduttività.

Altre sostanze sono state scoperte nella fase superconduttiva quando la temperatura raggiungeva quasi lo zero assoluto. Nel 1941, fu scoperto che una lega di niobio-nitruro diventava superconduttrice a 16 kelvin; allo stesso modo, nel 1953, si scoprì che il vanadio-silicio diventava superconduttore a 17,5 kelvin. Le temperature per la transizione alla superconduttività stavano lentamente aumentando. Sorprendentemente, molti buoni conduttori, come il rame, l'argento e l'oro, non mostrano superconduttività.

Superconduttore

Una sostanza che raggiunge la superconduttività, uno stato in cui i campi magnetici non possono penetrare e non c'è resistenza elettrica, viene definita ...

Education

Didattica

JoVE Core

Fisica

Unit 1

Unità 1

Electromagnetic Induction

Induzione elettromagnetica

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

superconductor critical temperature

Superconductivity is the state in which a material has no electrical resistance and magnetic fields cannot penetrate it. A material that reaches this state is called a superconductor. The key idea in the transcript is the critical temperature, which is the temperature at which the change happens.

Heike Kamerlingh Onnes of Leiden University first observed this behavior in mercury in 1911. He cooled a mercury sample in liquid helium to study how resistance changed with temperature. As the temperature fell, the resistance also fell. When the temperature approached 4.2 K, the resistance suddenly dropped to zero. That temperature is the critical temperature for mercury, and the mercury sample entered a superconducting phase with absolute zero resistance.

A normal conductor is different because its resistance is not zero, even when it is very small. In the transcript, conductors are described as having resistance less than 0.01 Ω. Very small resistances can be measured with methods such as the four-point method. An ohmmeter, however, is not acceptable for testing superconductivity resistance.

Other materials have also been found in the superconducting phase near absolute zero. In 1941, an alloy of niobium-nitride became superconducting at 16 kelvin. In 1953, vanadium-silicon became superconductive at 17.5 kelvin. These discoveries showed that transition temperatures were slowly increasing. Even so, many good conductors such as copper, silver, and gold do not show superconductivity.

Superconductor Critical Temperature

induction

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superconductor

Superconductivity is the state in which a material has no electrical resistance and magnetic fields cannot penetrate it. A material that reaches this state is called a superconductor. The key idea in the transcript is the critical temperature, which is the temperature at which the change happens. Heike Kamerlingh Onnes of Leiden University first observed this behavior in mercury in 1911. He cooled a mercury sample in liquid helium to study how resistance changed with temperature. As the...

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induced electric fields: applications

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electromagnetic fields

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key terms and concepts

Learn how superconductivity appears at a critical temperature, why mercury became a classic example, and how other materials also show zero resistance.

Superconductor Critical Temperature | JoVE K12

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Superconductor Critical Temperature

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