سوال ۲۴ کنکور ارشد مهندسی برق ۱۴۰۴

PASSAGE 3

Let's start with the basics. A superconductor is a material where electrical resistance disappears and a magnetic field is created. More simply, when you put electricity into a superconductor, you do not lose any energy—a multimeter would register zero volts and zero ohms on a live circuit—and it becomes a magnet. [1] We have known about superconductors since 1911, when a Dutch physicist named Heike Kamerlingh Onnes observed that when he immersed mercury wire in liquid helium, bringing its temperature down to within just a few degrees of Absolute Zero (-273.15°C or 4.2 Kelvin, to be precise) its electrical properties abruptly changed. He wrote, "Mercury has passed into a new state, which on account of its extraordinary electrical properties may be called the superconductive state." [2] In 1913, he won the Nobel Prize in Physics for his work.

This will not be the only Nobel Prize related to superconductors you will hear about. [3] When experimental physicists prove that something happens, theoretical physicists have to figure out the why of it. A lot of hypotheses were kicked around about superconductivity, as well as suggestions for practical applications. By the 1950s, the US physicists John Bardeen, Leon Cooper, and John Robert Schrieffer had an explanation for low-temperature superconductivity that everyone seems to agree on. [4] Electrons moving through a superconductor can pair up using quantum properties to evade the normal barriers to free movement through a solid. They proved mathematically that this pairing was possible in many substances up to a temperature of around 40 Kelvin, but higher than that the pairs of electrons would be shaken apart by the energy of the warm solid matter. Their work earned them the Nobel Prize in Physics in 1972.

24- In which position marked by [1], [2], [3] or [4], can the following sentence best be inserted in the passage?

Over the next two years, he discovered similar properties in tin, lead, then other metals and alloys including niobium-tin, all when cooled down to almost Absolute Zero.