Category Archives: Thermodynamics

Rhapsody in Blue

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118-1841_IMGLast Saturday we went to a fantastic concert at the Liverpool Philharmonic Hall.  It featured the pianist Michel Camilo playing the UK premier of one of his own compositions, Piano Concert No. 2 ‘Tenerife’ and Gershwin’s Rhapsody in Blue with the Royal Liverpool Philharmonic Orchestra.  He was fabulous – there are a couple clips on YouTube of him playing Rhapsody in Blue so you can some idea of what we experienced on Saturday evening.  I cannot play the piano and so his virtuosity was all the more impressive to me.  The applause at the end was ecstatic and followed by an even more spectacular encore, Caribe.

As we applauded for what seemed like a couple of minutes, I was reminded of an example that I had worked through in class last term for my first year undergraduate course in Thermodynamics.  The worked example is attached and involves estimating the temperature rise in palms of your hands as a consequence of vigorously clapping during which kinetic energy is converted into internal energy in the flesh of your palms and causes the temperature rise, ignoring the energy converted into sound.  The emphasis was on estimating by creating a model using a set of identified assumptions and, once we had an answer, I discussed the influence of those assumptions and introduced the idea of sensitivity analysis – this is not included in the worked example attached.

For twenty enthusiastic claps we found a temperature rise of a quarter of a degree Celsius, which we would probably notice since the hairless skin on the palm at the base of thumb is sensitive to changes as small as a twentieth of a degree, according to Dr Lynette Jones of MIT [doi:10.4249/scholarpedia.7955].

Hot particles

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diffraction pattern from nanoparticlesHave you ever wondered why people visiting the site of the Fukushima nuclear accident are only dressed up in coveralls and masks?  In my post on December 18th entitled ‘Hiding in the Basement’, I explained that gamma radiation requires a sheet of lead to stop it so the coveralls are clearly not protecting Fukushima visitors against radiation.

Our bodies cope with low levels of radiation everyday because we absorb about 0.024 Sieverts per year from the natural environment and the same amount is absorbed during a full-body scan in hospital.  One Sievert is equivalent to 1 Joule absorbed per kilogram of body mass. If you hold a tennis ball as high above your head as you can reach and let it fall to the ground, then the ball hits the ground with about 1 Joule of kinetic energy.  Your heart uses about 1 Joule of energy per beat.

The estimated maximum dose received by residents living close to Fukushima was 0.068 Sieverts or about three annual doses.  The visitors’ coveralls and mask are protecting them from ‘hot’ particles that are often produced during a nuclear accident. ‘Hot’ particles can be inhaled or ingested and continue to emit radiation when inside the body thus delivering a large concentrated dose to a relatively small number of surrounding cells, which are disrupted and destroyed by the high-levels of energy.  ‘Hot’ particles are small pieces of radioactive material and vary in size from tens of nanometres to a few millimetres, so that they don’t have high penetrating power and can be detected using a Geiger counter.

Hiding in the basement

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us highwayWhen we lived in the USA, I remember seeing billboards along the Interstate with messages from FEMA telling us ‘Be Ready’, to prepare, to plan, and to stay informed.  I was never quite sure what we were meant to be ready for since we lived in rural Michigan where we were fortunate not to experience violent weather and to be far from industrial plants that might explode and shower us with chemicals or radiation.  The billboard advertised the FEMA website [www.ready.gov] which contains very little factual information about radiation but does imply you should seek shelter in the basement of tall buildings in the event of a nuclear accident. Some commentators have suggested that the psychological effects arising from fear of nuclear radiation can cause more health issues than the dosage received especially for those not in the immediate vicinity of an incident.  So, knowing more about radiation in advance of an incident would be helpful and might also dispel many of the fears that cause opposition to nuclear energy.

So, does sheltering in a basement offer reasonable protection?  Well, radiation is produced when radioactive materials decay and their atoms release protons and neutrons from their nucleus plus some of the electrons that orbit the nucleus.  The protons and neutrons cluster together to form alpha particles (actually Helium nucleii) that are relatively massive and can stopped by a sheet of paper.  The electrons, known as beta radiation, whizz out at high-speed but can be stopped by a thin sheet of Aluminium.  High-energy photons are also released with the electrons and are known as Gamma radiation, which requires a sheet of lead or a considerable thickness of concrete to stop them.

So sheltering in the basement is a good idea especially if the building above contains a substantial amount of concrete.

Sources:

http://www.ready.gov/nuclear-power-plants

David Ropeik, Fear vs. radiation: The mismatch, in the International New York Times, Tuesday October 22, 2013. http://www.nytimes.com/2013/10/22/opinion/fear-vs-radiation-the-mismatch.html?_r=0

Zen and entropy

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Picture1Last weekend I went to a performance of Handel’s Messiah in our local cathedral.  The atmosphere in the vast cathedral was wonderful and for part of the performance I was transformed into a zen-like state by the music.

However, there were quite of lot of disturbances during the performance including some that went beyond the usual coughing and sneezing.  It is interesting that a sneeze in the quiet environment of a cathedral or library causes a large disturbance while the same sneeze in a busy street goes unnoticed.  Of course, it is about the change in the noise level, and as a percentage, the added noise of a sneeze is much greater in the quiet library than the busy street.  Noise is a form of energy that becomes dispersed and dissipated as it propagates and so it is easy to equate it to heat which exhibits the same behaviour.  Heat transfers from hot to cold places while noise propagates from loud to quiet places, and neither does the reverse, which was Clausius’ observation that lead to the Second Law of Thermodynamics.  Clausius also defined change in entropy as the heat transfered divided by the temperature at which it occurs.  So the same heat transfer creates more entropy at low than at high temperatures, just as a sneeze causes more disorder/disruption in a quiet than a loud environment.  We can equate entropy to the level of disorder present in any system or environment.

And the second law of thermodynamics states that the entropy of an isolated system will always increase until it reaches a maximum at equilibrium.