A Leslie’s cylinder for a couple of quid.

The main aim of the FUNcube project is provide educationalists access to information about a real spacecraft in Low Earth Orbit. Please use this forum to discuss classroom projects and similar matters. FUNcube support is provided elsewhere in the forum.

Moderators: pa3weg, g4dpz, admin

A Leslie’s cylinder for a couple of quid.

Postby JohnG7OHO » Tue Jun 17, 2014 8:27 am

You don’t need to spend $400 for Pasco’s Leslie’s cube (http://www.pasco.com/prodCatalog/TD/TD- ... lies-cube/) or £40 from Philip Harris. An empty baked bean tin will do just the job! Make sure the lid is still attached though. I painted one half matt black from a tester pot, for £1.99. Add boiling water, stir occasionally. I used a thermocouple and obtained these readings: shiny side 0.2 mV, black 1.3 mV. A dramatic difference.
You don’t need a thermocouple to prove that a black surface is a better emitter of heat radiation than a shiny surface - just bring the palms of your hand close to the can. The important point is that both sides, shiny and black, are at the same temperature. The water needs to be stirred, the wall of the can is a good conductor - so both halves of the can are at the same temperature. That’s the whole point of the Leslie’s cube. The heat radiated from each surface is different.
We mustn’t trust our senses to guess a temperature (remember the three bowls of water experiment!) but if you momentarily touch the outside of the can the shiny side actually feels hotter than the black! You mustn’t trust an IR thermometer either! Pointing it at the two surfaces gave these results: shiny 31oC, black 89oC. I don’t think so!
JohnG7OHO
 
Posts: 10
Joined: Mon May 12, 2014 1:32 pm

Return to Schools

Who is online

Users browsing this forum: No registered users and 1 guest

cron