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Chapter 24: Problem 5

Why can current persist forever in a superconductor with no applied voltage?

Short Answer

Expert verified
In a superconductor, due to zero electrical resistance, once an electrical current is established, it can persist indefinitely without the need for any applied voltage. This is because the current does not lose any energy as heat, which typically occurs in other conductors because of resistance.

Step by step solution

01

Understanding Superconductivity

Superconductivity is a quantum mechanical phenomenon observed in certain materials at very low temperatures, where they lose all electrical resistance. This characteristic makes them unique and able to conduct an electric current indefinitely without any power source. This is because the electrons in a superconductor move in pairs (Cooper pairs), unlike in normal conductors where they move individually.
02

The effect of zero electrical resistance

All ordinary conductors exhibit some resistance to the flow of electricity. This resistance causes power loss, typically in the form of heat. In a superconductor, because the resistance is zero, an initial current flowing in a closed loop of superconducting wire can persist indefinitely with no additional power input. This is because no energy is lost in the form of heat.
03

The role of applied voltage

Voltage, in essence, is the push that motivates charges to move and create current. In normal conductors, an applied voltage drives the current, overcoming the material's resistance. However, in a superconductor, once the current is established, it can remain indefinitely without a continuous voltage input due to the absence of energy loss mechanisms.

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Most popular questions from this chapter

A copper wire joins an aluminum wire whose diameter is twice that of the copper. The same current flows in both wires. The density of conduction electrons in copper is \(1.1 \times 10^{29} \mathrm{m}^{-3} ;\) in aluminum it's \(2.1 \times 10^{29} \mathrm{m}^{-3} .\) Compare (a) the drift speeds and (b) the current densities in each wire.

A constant electric field generally produces a constant drift velocity. How is this consistent with Newton's assertion that force results in acceleration, not velocity?

Metallic conductors like lightbulb filaments and electric stove burners have resistance that increases with increasing temperature. During the brownout, the current in such devices a. decreases by \(10 \%.\) b. decreases by more than \(10 \%.\) c. decreases by less than \(10 \%.\) d. You can't tell without knowing more about how the resistance varies.

An incandescent lightbulb draws \(0.50 \mathrm{A},\) while a compact fluorescent with the same light output draws 125 mA. Both operate on standard \(120-\mathrm{V}\) household power. How do their energy-consumption rates compare?

A \(50-\mathrm{W}\) and a \(100-\mathrm{W}\) light bulb are both designed to operate at \(120 \mathrm{V}\). Which has the lower resistance?
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