Yr12 Assessment Task: Superconductors
Section 1:
Statement 1:
Henry and Lawrence Bragg used X-ray diffraction to determine the crystal structure of various materials. X-rays were passed through a metal of various crystal salts including Sodium Chloride and Zinc Sulphide. A sheet of photographic film was placed in the exiting path of the X-rays, in order to receive the diffraction patterns. Bright spots were observed on the photographic film. In order to determine the internal structure of the crystal, the angles between the spots on the photographic film could be calculated. Braggs Law, mathematical expressions, provides an explanation of the X-ray patterns, and their experiment allowed for the discoveries of a number of crystal structures.

Statement 2:
In order to conduct electricity, electrons must travel in the space between lattice layers of a material. When electrons travel through the lattice unimpeded, there is no resistance, as no internal or external force is stopping the electron to pass through freely. In turn, resistance is high when electrons path is obstructed. This can happen by either internal or external factors. Impurities in a metal distort the lattice structure and impede the flow of electrons, as a path for them to travel will thus be obstructed. Sequentially, resistance of the metal is increased as the electrons cannot travel between the lattices unimpeded. Likewise, external factors may also impact the resistance of a metal. When a metal is heated, it gains energy and thus the lattices of the material vibrate. This vibration distorts the ability of the electrons to flow through the circuit freely, and hence causes resistance within the metal. Resistance is dependent on the internal and external environments that may affect it.
Statement 3:
The BCS theory is the idea of lattice distortions at low temperatures forming cooper pairs. This theory explains superconductivity in type 1 superconductors (those with critical temperature below 30K), and was put together by scientists Bardeen, Cooper and Schrieffer. As material reaches its superconducting state, very little to no vibrations occur within the lattice structure, allowing electrons to pass through unimpeded. Electrons are drifting past many positive metal atoms, and attract these positive ions so that a slight bend occurs in the lattice, at the attraction point. This, in turn, creates a region of increased positive charge. The second electron following, is attracted to this continuous positive region created by the original electron, hence travelling in a pair known as a ‘Cooper Pair’.

Statement 4:
Superconductors have various benefits and limitations and can widely impact both society and the environment.
Benefits:
- Conduct with zero resistance
- No waste current/heat
- Reduce size of computer chips, motors and generators
- Large quantities of energy release without heat loss

Limitations:
- Restricted operating temperatures
- Brittle
- Impractical due to constant need of liquid nitrogen
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