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Chapter 17: Problem 1

Give an account of the experimental results which distinguish the superconducting state from the normal of a metal.

Short Answer

Expert verified
Superconductors are characterized by zero electrical resistance, expulsion of magnetic fields (Meissner effect), and persistent currents below a critical temperature.

Step by step solution

01

Understanding Superconductivity

Superconductivity is a state in certain materials where they exhibit zero electrical resistance below a critical temperature. This allows electric current to travel without losing energy.
02

Critical Temperature

Identify the critical temperature (Tc) of the metal by cooling it down and observing the abrupt loss of electrical resistance. This is one key experimental feature of the superconducting state.
03

Zero Electrical Resistance

Measure the electrical resistance of the metal as it is cooled below its Tc. In its superconducting state, the resistance will drop to zero, which is different from its normal state where the resistance is always finite.
04

Meissner Effect

Demonstrate the Meissner effect, which occurs when the material expels all magnetic field lines upon transitioning to the superconducting state. This is tested by placing the metal in a magnetic field and cooling it below Tc to observe the expulsion of the magnetic field.
05

Persistent Currents

Show that superconductors can maintain persistent currents. Set up a loop of the superconducting material and induce a current. If the current persists without decay over time, it confirms the superconducting state.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Critical Temperature
The Critical Temperature (Tc) is a pivotal concept in superconductivity. This is the temperature below which a material transitions to its superconducting state.
To determine the Tc of a material, you gradually cool the substance down while monitoring its electrical resistance. At a specific temperature, the electrical resistance will drop sharply to zero.
This sudden change is a clear indicator that the material has become superconductive. Critical temperature varies for different materials. For example, mercury becomes superconducting below approximately 4.2 K.
Zero Electrical Resistance
A hallmark of the superconducting state is zero electrical resistance. In a normal conductor, electrical resistance causes energy loss as heat. However, below the critical temperature, superconductors exhibit no resistance; this is revolutionary for efficient energy transmission.
An experiment to measure this involves cooling the material below its critical temperature and passing an electric current through it. If the material is superconductive, instruments will detect no drop in voltage across it, signifying zero resistance.
Meissner Effect
The Meissner Effect is another key characteristic of superconductors. When a material transitions into the superconducting state, it expels all magnetic field lines from its interior.
You can observe this by placing the material in a magnetic field and cooling it down below its critical temperature. As it becomes superconducting, the magnetic fields will be expelled from the bulk of the material. This results in phenomena such as magnetic levitation. For example, a small magnet placed above a superconducting material will start to float.
Persistent Currents
Persistent currents are a defining property of superconductors. These are electric currents that flow indefinitely without any applied voltage once the material is in the superconducting state.
To demonstrate this, create a loop of superconducting material and induce a current in the loop. In a superconducting state, this current will persist for an extremely long time without decaying, thanks to the absence of electrical resistance. This phenomenon has crucial implications for maintaining stable magnetic fields in devices such as MRI machines.

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Most popular questions from this chapter

Calculate the critical current which can flow through a long thin superconducting wire of aluminium of diameter \(10^{-3} \mathrm{~m}\). The critical field for aluminium is \(7.9 \times 10^{3} \mathrm{~A} / \mathrm{m}\).

A superconducting lead has a critical temperature of \(7.26 \mathrm{~K}\) at zero magnetic field and a critical field of \(8 \times 10^{5} \mathrm{~A} / \mathrm{m}\) at \(0 \mathrm{~K}\). Find the critical field at \(5 \mathrm{~K}\).

Explain the formation of Cooper pair in a superconductor. Obtain an expression for the energy gap in a superconductor at absolute zero temperature.

The penetration depths for lead are \(396 \mathrm{~A}\) and \(1730 \mathrm{~A}\) at \(3 \mathrm{~K}\) and \(7.1 \mathrm{~K}\), respectively. Calculate the critical temperature for lead.
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