Physics update course December 2012

Friday 14th December

Due to teaching my lovely year 13 students I wasn’t able to attend Friday’s lectures so what I am writing for this section is just a summary of what I missed.

Tracking magnetic fields with SQUIDs

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Dr Samuel Henry Department of Physics University of Oxford http://www.physics.ox.ac.uk/users/henry/ http://www2.physics.ox.ac.uk/contacts/people/henry

SQUIDs (Superconducting Quantum Interference Devices) are high precision instruments used to track magnetic fields.

Dr Henry and his team have built such an instrument for their cryoEDM experiment which aims to study the asymmetry between matter and antimatter by measuring the neutron electric dipole moment. They have found that it may have further applications in geophysics, studying the flow of underground water, and possible earthquake precursor signals.

http://hyperphysics.phy-astr.gsu.edu/hbase/solids/squid.html

The crystal world

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Professor Mike Glazer Department of Physics University of Oxford

http://www2.physics.ox.ac.uk/contacts/people/glazer http://www2.physics.ox.ac.uk/events/2012/03/12/public-lecure-crystal-world-prof-michael-glazer

The sheer beauty of crystals has fascinated people for centuries, but it is only in the last 300 years or so years that they have been studied scientifically.

Prior to 1912, much of what was known about what crystals were – and what they were made of – was conjecture based on little more observation than of their external forms. Various scientists, including Kepler, Hooke and several others, developed theories that suggested some sort of repeating elements as being the necessary requirement to make a crystal.

In the nineteenth century, in particular, ideas about crystal symmetry came to the fore and this was used to classify different types of crystal. However, in early 1912, Laue, Friedrich and Knipping, working in Munich, were able to show that X-rays could be diffracted by crystals, the main aim of this work being to demonstrate that X-rays consisted of waves rather than particles.

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http://www.spartacus.schoolnet.co.uk/GERlaue.htm http://en.wikipedia.org/wiki/Max_von_Laue http://en.wikipedia.org/wiki/Friedrich_Reinitzer http://en.wikipedia.org/wiki/X-ray http://en.wikipedia.org/wiki/X-ray_crystallography

However, Laue made a number of incorrect assumptions about the results and it was William Lawrence Bragg, at the young age of 22, who showed how Laue’s experiments could be interpreted in a memorable publication of November 11th 1912.

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http://en.wikipedia.org/wiki/William_Lawrence_Bragg http://en.wikipedia.org/wiki/William_Henry_Bragg

In particular W L Bragg was able to determine the crystal structure of Zinc Sulphide (http://en.wikipedia.org/wiki/Zinc_sulfide), and thus he heralded in the modern subject of X-ray crystallography. He carried on working together with his father William Henry Bragg publishing a series of important papers in 1913-1914, interrupted subsequently by the First World War. Laue was awarded the Nobel Prize for physics in 1914, and both father and son Bragg shared the Nobel Prize in 1915. The younger Bragg still remains the youngest Nobel Prize winner ever.

The two Braggs continued to make important scientific contributions, and their work has led to in excess of 23 Nobel Prizes.

http://en.wikipedia.org/wiki/Crystal

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