Question

Calculate the depth inside a

superconducting material where magnetic field becomes 90% less of its initial

value.​

Answer 1

Answer:

1 Superconductivity

Superconductivity was discovered in 1911 by Heike Kamerlingh Onnes (Figure 1) as he studied the properties of metals at low temperatures. A few years earlier he had become the first person to liquefy helium, which has a boiling point of 4.2 K at atmospheric pressure, and this had opened up a new range of temperature to experimental investigation. On measuring the resistance of a small tube filled with mercury, he was astonished to observe that its resistance fell from ~0.1 Ω at a temperature of 4.3 K to less than 3  ×  10  −6 Ω at 4.1 K. His results are reproduced in Figure 2. Below 4.1 K, mercury is said to be a superconductor, and no experiment has yet detected any resistance to steady current flow in a superconducting material. The temperature below which the mercury becomes superconducting is known as its critical temperature Tc. Kamerlingh Onnes was awarded the Nobel Prize for Physics in 1913 ‘for his investigations on the properties of matter at low temperatures which led, inter alia, to the production of liquid helium’ (Nobel Prize citation).

Figure 1

Figure 1 Heike Kamerlingh Onnes (left) and Johannes Van der Waals beside a helium liquefier (1908).

Figure 2

Figure 2 Graph showing the resistance of a specimen of mercury versus absolute temperature.

Explanation: