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Chapter 24: Problem 5

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

Short Answer

Expert verified
The current can persist forever in a superconductor with no applied voltage because superconductors exhibit zero electrical resistance. Once a current is started in such a conductor, it can continue indefinitely since there's no resistance to cause energy loss.

Step by step solution

01

Understanding Superconductors

Superconductors are materials that can conduct electricity with zero electrical resistance. This rarity is brought about by decreasing the temperature of certain materials to the point where their resistive properties disappear. Due to this characteristic, electrical current can move through these materials with no energy loss.
02

Explaining Persistence of Current

The persistence of current in a superconductor is due to the absence of electrical resistance. In a standard conductor, resistance impedes the flow of electrons and causes energy loss in the form of heat. However, this is not the case with superconductors. Since there's no energy loss, once a current is initiated in a superconductor, it can theoretically persist forever without the need for any applied voltage.
03

Note on Perfect Superconductors

This phenomenom, though, is ideally applicable to a perfect superconductor. In the real world, there might still be impurities or thermal vibrations in the superconductive material, causing some minimal resistance that eventually lead to decay of current. However, the current decay time in such a real superconductor can still be astronomically long and for all practical purposes, the current is considered to persist forever.

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Most popular questions from this chapter

A car's starter motor draws 125 A with 11 V across its terminals. What's its power consumption?

A brownout occurs when an electric utility can't supply enough power to meet demand. Rather than cut off some customers completely, the utility reduces the voltage across its system. Brownouts are most likely on hot summer days, when heavy air-conditioning loads drive up demand for electricity. In a particular brownout, the utility reduces the voltage by \(10 \%.\) Which of the following occurs in the conductors of the preceding problem during the brownout? a. Both the electric field and electron drift speed decrease. b. The electric field decreases but the electron drift speed doesn't. c. The current is carried by fewer electrons. d. The electrons undergo more frequent collisions.

You're heading out for spring break, but your car won't start. Your friend says you might have corrosion at the battery terminals-a frequent cause of hard starting because of increased resistance. Having read Example 24.4, you know that the resistance between battery and starter should be around \(1 \mathrm{m} \Omega\). While your friend cranks the starter, you measure \(4.2 \mathrm{V}\) between the battery terminal and the wire carrying current to the starter motor. If the motor draws \(125 \mathrm{A},\) is the resistance in its normal range?

A \(12-V\) car battery is rated at 80 ampere-hours, meaning it can supply 80 A of current for 1 hour before it becomes discharged. If you accidentally leave the headlights on until the battery discharges, how much charge moves through the lights?

A brownout occurs when an electric utility can't supply enough power to meet demand. Rather than cut off some customers completely, the utility reduces the voltage across its system. Brownouts are most likely on hot summer days, when heavy air-conditioning loads drive up demand for electricity. In a particular brownout, the utility reduces the voltage by \(10 \%.\) During the brownout, the power dissipated in conductors whose resistance is nearly independent of temperature a. decreases by approximately \(10 \%.\) b. decreases by approximately \(20 \%.\) c. decreases by approximately \(5 \%.\) d. You can't tell without knowing the resistance.
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