Competition for Pluto

See my other blog for a post about Pluto.

Progress with superconductors

Superconductors are materials which have zero resistance and can therefore carry high currents with no energy loss due to heating. At present such materials only superconduct at low temperatures requiring cooling.

This is a quote from a report about the progress being made to use such materials in electrical generators as used in power stations. Any small increase in efficiency saves a lot of energy and money. There are references to several Physics concepts including electrical power and efficiency, temperature, heating, centrifugal force as well as superconductivity. Although not yet in the syllabus the term "superconductivity" is becoming important enough that any educated citizen should know what it means.

"The experts from Corporate Technology — the central research organization at Siemens — have acquired a great deal of experience with regard to electric motors and generators whose coils are made from high-temperature superconductors. These superconductors have an operating temperature of around minus 240 degrees Celsius. The electric current density possible with such windings is approximately 30 to 100 times greater than the values achievable with copper coils at room temperature. Following tests on a 400-kilowatt model motor, a four-megawatt (MW) generator operating at 3,600 rpm was subjected to a program of long-term tests. This was followed by tests on a 4 MW high-torque motor at 120 rpm. Each of these projects showed that the high-temperature superconductor technology halved the machines’ losses while also reducing their size and weight. "

Calibrating a thermometer

We recently did a standard calibration exercise using melting ice and boiling water. We calibrated some alcohol-in-glass thermometers which had broken threads. Some things we learnt:

• make sure the thermometer is in good contact with the ice (well crushed ice is best)
• there is a small difference between the temperature of the steam and that of the boiling water
• the thermometers with the broken threads were several degrees in error for both fixed points

It was a useful activity and also teaches that instruments do not always give correct readings!

No displacement can?

A displacement can is usually used to investigate Archimedes Principle. It is used to deliver displaced liquid into a waiting beaker for weighing.

However if no displacement can is available a beaker can give a good result if precautions are used.

Firstly some petroleum jelly is smeared under the 'spout'.

Secondly the small beaker used to catch the over flow needs to be close and under the 'spout' as shown in the diagram.

Some Modern Physics videos

Some vidoes I found useful:
Millikan's oil drop experiment to find e - an good animation of the experiment
Specific charge on the electron e/m - a good video of an actual demo

Do-it-yourself: centripetal force

This device demonstrates centripetal force. Just hold it vertically and whirl it gently so that the top weight circles around. Speed up the motion and the bottom weight rises as the centripetal force increases.

I used a pair of old keys as weights. Takes a bit of practice but is easy enough.

Materials: drinking straw, sewing thread, two weights. A glass tube or plastic tube should also work instead of the straw.

Do-it-yourself lab equipment

I will be periodically (hopefully once per month) adding ideas for making simple equipment for use in the Physics lab or for demos.