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

超伝導体は、電子の流れに対する抵抗がゼロで、電気エネルギーを効率的に伝達し、熱損失がない材料です。
1911年、Heike Kamerlingh Onnesは、水銀が4.2ケルビン未満に冷却されると抵抗がゼロになることを観察しました。これは水銀の臨界温度として知られており、この現象は超伝導として知られています。
温度が臨界温度を超えると、抵抗はそれに伴って直線的に変化します。
超伝導体の磁気挙動の別の側面は、均質な超伝導材料が外部の均一な磁場に置かれたときに観察されます。
温度が臨界温度よりも高い場合、材料内部の磁場は外部の均一な磁場に等しくなります。臨界温度よりも低い場合、磁束は材料から放出され、その中の磁場はゼロになります。この現象はマイスナー効果として知られています。
臨界温度を下回る材料の超伝導は、臨界磁場として知られる最小の大きさの磁場を適用することで排除できます。

<ol>
	<li>OpenStaxです。(2019). 大学物理学 Vol.2.[Web版]、396〜398ページ。<a href="https://openstax.org/books/university-physics-volume-2/pages/9-6-superconductors"から取得>https://openstax.org/books/university-physics-volume-2/pages/9-6-superconductors</a></li>
</ol>

超電導体

磁場が透過できず、電気抵抗が存在しない超伝導状態に達した物質を超伝導体と呼びます。 1911 年、オランダの物理学者であるライデン大学のヘイケ・カメルリング・オンネスは、温度と水銀元素の抵抗との関係を観察しました。 次に、水銀サンプルを液体ヘリウムで冷却して、温度に対する抵抗の線形依存性を研究しました。 温度が低下するにつれて抵抗が低下することが観察されました。 Kamerlingh Onnes は水銀サンプルをさらに冷却し続け、温度が 4.2 K に近づくと、抵抗は突然ゼロになりました。 これは水銀の臨界温度であり、水銀サンプルは抵抗が絶対ゼロの相に入り、この現象は超伝導として知られています。 導体の場合、抵抗はゼロではありませんが、0.01 未満です。 非常に小さな抵抗を測定するには、4 点法などのさまざまな方法がありますが、超電導抵抗の試験には抵抗計は使用できません。

温度が絶対零度近くに達したときの超伝導相では、他にもいくつかの物質が発見されています。 1941 年に、窒化ニオブの合金が 16 ケルビンで超電導になることが発見されました。 同様に、1953 年にはバナジウムシリコンが 17.5 ケルビンで超電導になることが発見されました。 超伝導への転移温度はゆっくりと上昇していきました。 驚くべきことに、銅、銀、金などの多くの良導体は超電導を示しません。

磁場が浸透できず、電気抵抗がない状態である超伝導に達する物質は、...

Education

JoVE Core

物理学

Unit 1

ユニット1

Electromagnetic Induction

電磁誘導

KEY TERMS AND CONCEPTS

主要用語と概念

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

Magnetic Flux and Induced Current

Magnetic flux and induced current are linked when a magnetic field changes near a coil. Moving a bar magnet into or out of a coil induces an emf, which is an electromotive force. If the motion goes in the opposite direction, the emf has the opposite sign. Reversing the magnet poles also reverses the direction of the induced emf. The same effect appears when the coil moves instead of the magnet. Relative motion is what matters. A faster motion produces a larger emf. If the magnet and coil stay...

ampere-maxwell's law: problem-solving

Displacement Current in an RC Circuit

Displacement current in an RC circuit can be found by tracking the charging capacitor. A parallel-plate capacitor with capacitance C, plate area A, and plate separation d is connected to a resistor R and a battery of voltage V. When the current starts to flow at t = 0, the charge and voltage on the capacitor change with time. The first step is to use the RC-circuit result for the capacitor voltage at time t. With the z-axis pointing from the positive plate to the negative plate, the electric...

differential form of maxwell's equations

Maxwell’s Equations at a Point

Maxwell’s equations at a point describe how electric and magnetic fields change in space and time. They connect field behavior to charge and current density at a single location. This point-by-point form is useful when studying electromagnetic fields in detail. James Clerk Maxwell was a major physicist of the nineteenth century. He combined earlier laws of electricity and magnetism into one electromagnetic theory. The basic experimental laws came from scientists such as Oersted, Coulomb,...

dc generator

How a DC Generator Makes Current

A DC generator makes electrical energy from mechanical motion. It produces DC pulses with the same polarity, unlike an alternator, which gives sinusoidal AC current. The two machines have similar construction, but a DC generator uses a single split ring instead of a pair of slip rings. That split ring is called a commutator. It works like a rotary switch that changes the contact with the brushes after each half turn of the conducting loop. This action keeps the induced emf at the same...

magnetic damping

Eddy Currents and Magnetic Braking

Eddy currents can create strong drag on moving objects. This drag is called magnetic damping. A metallic pendulum bob swinging between the poles of a strong magnet feels this force as it enters and leaves the field, so its motion dies out quickly. The effect is much smaller for a slotted metal plate. As the plate enters the magnetic field, a changing flux induces an emf, or electromotive force. The slots limit the size of the current loops, and nearby loops can carry currents in opposite...

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...

types of superconductors

Superconductors and Magnetic Levitation

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faraday's law

Magnetic Flux and Induced Emf

Faraday’s law connects magnetic flux changes to induced emf, or voltage. A change in the magnetic field or in the coil’s orientation with respect to the field can produce this voltage. Magnetic flux describes how many magnetic field lines pass through a given surface area.

lenz's law

Magnet Motion and Induced Current

Magnet motion and induced current are linked by Lenz’s law. The law says that the induced emf, or electromotive force, drives current around a wire loop in a direction that opposes the change in magnetic flux that caused it. A moving bar magnet can create this effect in a coil. If the magnet moves toward the coil, the magnetic flux increases and an induced current appears. That current produces a magnetic field that pushes against the stronger field from the magnet. The same idea works in...

motional emf

Induced Current from Changing Magnetic Flux

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faraday disk dynamo

Faraday Disk Dynamo and DC Output

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induced electric fields

Faraday’s Law and Induced EMF

Faraday’s law explains how a changing magnetic flux can create an induced emf in a circuit. When current is induced, work is being done on the conduction electrons in the wire. That work must come from a source, and the source is not a battery or a magnetic field. A battery does not have to be present in a circuit for current to be induced. Magnetic fields also do not do work on moving charges. Instead, the change in magnetic flux produces an electric field in the wire. This is called an...

induced electric fields: applications

Electric Fields from Changing Magnetism

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eddy currents

Eddy Currents in Recycling, Brakes, and Heat

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displacement current

Maxwell’s Fix for Changing Currents

Maxwell’s correction to Ampère’s law explains how changing electric fields can create magnetic fields. The key idea is the displacement current, Id, which Maxwell added to the real conduction current, I. This extra term helps the law work when current is not steady. The displacement current is defined using the permittivity of free space, ε0, and the electric flux, ΦE. It is not a real flow of charge. Instead, it is an added term in Maxwell’s equations that acts like current in Ampère’s law. <br...

significance of displacement current

Maxwell’s Fix for Charging Capacitors

Maxwell’s fix for a charging capacitor is the displacement current in Ampère’s law. A displacement current is not a flow of charge like conduction current. It comes from a changing electric field. That is why it is defined using a time-varying electric field and has its own displacement current density. Maxwell added this term to the original Ampère’s law. The result is called generalized Ampère’s law. The added displacement current term lets the law work in regions where no charges are moving.

electromagnetic fields

Electric and Magnetic Fields in Motion

Electric and magnetic fields can come from different sources, but they can act in surprisingly similar ways. Static charges create electrostatic fields. These fields are conservative, which means a test charge does no net work after moving around a complete loop. Fields made by changing magnetic fields behave differently. They are not conservative, and they do net work on a charge. That work is proportional to how fast the magnetic flux changes. These fields also do not follow Gauss’s law for...

maxwell's equation of electromagnetism

Maxwell's Equations and Light Waves

Maxwell's equations bring electricity, magnetism, and light together in one electromagnetic theory. James Clerk Maxwell was a major nineteenth-century physicist, and his work helped shape modern physics. He also made important contributions to the kinetic theory of gases, color vision, and the study of Saturn's rings. Maxwell built on earlier experiments in electricity and magnetism from Oersted, Coulomb, Gauss, and Faraday. These physicists had discovered the basic laws separately. Maxwell...

symmetry in maxwell's equations

Electric and Magnetic Field Symmetry

Electric and magnetic field symmetry is a key part of Maxwell's equations. After the fields are calculated with Maxwell's four equations, the Lorentz force equation gives the force those fields exert on a charged particle moving at a certain velocity. The Lorentz force law combines the effect of the electric field and the magnetic field on the moving charge. Maxwell's equations and the Lorentz force law together describe electricity and magnetism. The symmetry in Maxwell's framework is easier...

electric generator: alternator

How Alternators Produce AC Power

Alternators produce alternating current by rotating a conducting loop in a magnetic field. As the loop turns inside the field, the magnetic flux through the coil changes with time. That changing flux induces an emf, or electric voltage, in the circuit. A simple alternator uses a loop placed in a uniform magnetic field. The loop connects to split rings, and brushes carry the current to the external circuit. As the loop rotates, the magnetic flux changes sinusoidally, so the induced emf also...

back emf

Motor Current and Speed Changes

Motor current and speed changes are linked by back emf in an electric motor. A motor sends current through a wire loop in a magnetic field. The magnetic field pushes on the loop and creates torque, which turns a shaft and does mechanical work. As the coil turns, the magnetic flux through it changes. That changing flux induces an emf, or voltage, by Faraday’s law. The motor then acts like a generator whenever its coil rotates, whether the shaft is turned by an external drive or by the motor...

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

physics

JoVE Core 物理学は、運動学、力学、流体力学、静力学、波動、音響などの基礎的な物理学の理論と応用を、簡潔でわかりやすいアニメーション ビデオで紹介します。さらに、科学者の実際のビデオでは、世界中の今日の研究所で行われている古典的および独自の研究実験における関連概念の適用を示しています。

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Superconductor Critical Temperature

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