Conductivity of Glass

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Harvard Natural Sciences Lecture Demonstrations

12 жыл бұрын

Insulating glass becomes a conductor of electricity when heated with a blowtorch.
Two ceramic lightbulb sockets are wired in series to a household AC power cord. When two incandescent bulbs of the same Wattage rating are screwed into the sockets and the cord is plugged in, they both pass the same amount of current and so they both light with the same intensity. When one bulb is unscrewed, the circuit is broken and the other bulb goes out. If we can replace the missing bulb with a conductive material, the circuit will once more be complete and the remaining bulb will light again.
For more details on our setup, see sciencedemonstrations.fas.harv...

Пікірлер: 34

@NatSciDemos 12 жыл бұрын

@tonsilol The bulb we removed at 0:15 is not the same as the one we smashed at 0:24--that bulb died a natural death. No incandescent bulbs were harmed in the making of this movie.

@venky4993 4 жыл бұрын

For human human rights for animals animal rights and now for bulbs bulb rights laws lok

@ildonaldson 11 жыл бұрын

What a fine demonstration. I've been trying to do this experiment with a heated glass rod - as found in most households - (joke!) - but this is much simpler. A really beautiful experiment. Well done!

@NatSciDemos 11 жыл бұрын

thanks! we used to do the glass rod version but it was not very reliable. this way we get to re-use incandescent bulbs that have burned out.

@Dr.HazharGhaderi 12 жыл бұрын

Perfect demo, loved it.

@user-le8cp8sx9t 2 жыл бұрын

Very interesting experiment! Thank you :)

@jcjlf 9 жыл бұрын

Very instructive. I used to do this myself with a glass rod, but this is better. LIKE

@chadx8269 2 жыл бұрын

Nice demo of conductive of molten glass. Where in electron are excited into the conduction band. Consider doping the molten glass with boron.

@vincentpol 12 жыл бұрын

This is exactly how my dimmer works. I blowtorch the house down to get the right light setting.

@ianviljoen9036 6 жыл бұрын

Wow....mind blown!

@WhatAWondWorld 2 жыл бұрын

Шикарно!

@electroumit 8 жыл бұрын

Thank you.

@Speeder84XL 10 жыл бұрын

Hahha - very nice! I did know that heated glass will conduct electricity but not that good. If you connect something that draws a little more current thru that glass it would be self sustaining as when the glass cools the resistance goes up and that will cause heat and prevent it from cooling down. If it's very much current going thru, the glas will probably melt though. There will also always be some voltage drop thru it as of course as it takes some power to keep it hot

@DanielRosenberg 10 жыл бұрын

Yes. We pick the lightbulb so that the current through the molten glass heats itself to a steady state. Not so much that it melts, not so little that it goes out. In fact, if one blows on the molten glass as if it were a candle, it cools enough for the system to stop conducting, and the bulb goes out.

@Elektronaut 12 жыл бұрын

beloved opaque bulbs :-(

@tahanlaoboy 2 жыл бұрын

The heat helps the electricity to travel to the glass, its mean the heat and glass combine to conduct electricity

@socialstatus7554 3 жыл бұрын

Silly concepts is there.. In molten glass, ions of silica conduct electricity by flow of electron... is this concept is right then don't forget to reply or I like it thank you.

@serkanozkani 4 жыл бұрын

That's how semıcondctors works?

@NatSciDemos 4 жыл бұрын

Sort of. Yes it is true that the conductivity of semiconductors such as silicon increases with temperature, and glass is generally silica-based. What's also happening here is that as the glass becomes molten, charge carriers are able to become a little more mobile than they are at room temperature. As a practical matter most transistors work by applying a voltage rather than a blowtorch.

@kamalmichael 12 жыл бұрын

r u sure the wires didnt melt ,fused together and made contact? ...although i hv to admit, the light came on very slowly which suggest u r correct

@pvc988 9 жыл бұрын

Known fact... They are connected in series so that is obvious that if one lights up the second will do the same. It doesn't matter that the broken one emits the light because of the heat from a propane torch. Or maybe is it because electricity conducts heat very well and the heat from broken bulb goes, thru electricity, to the other one and makes it light up? Now I feel confused.

@75L48 5 жыл бұрын

What the hell.. this is stupidest toughts I have ever read. Go educate yourself, you have NO idea about anything. :D Yea i deducted that from you reply, thats how bad it is.

@1.4142 2 жыл бұрын

The opposite effect with normal wires

@coffeecuppepsi 4 жыл бұрын

practical application: arduino compatible lava sensor

@irun_mon 8 жыл бұрын

burn the electron

@Walkingdeadman1991 12 жыл бұрын

Nothing a Blow Torch can't solve, it can even solve the nasty neighbour.

@Dr-Shlomo-Cohen 7 жыл бұрын

or, you could just use a switch. (just kidding)

@ericbergfield6451 10 жыл бұрын

Isn't it obvious that melted glass would be a conductor? It's clearly a liquid.

@bobbycondon5059 10 жыл бұрын

Just because something is liquid does not make it a conductor, for instance pure water is actually an insulator its the impurities in it that are conductive.

@Rottdog300 10 жыл бұрын

Bobby Condon I remember being shown that when i was in high school. An stripped plug was submerged in water and plugged into the wall. My Teacher then put his finger in the water and it was fine. After That he dropped a penny in the water and it started to sizzle and smoke. That was definitely a cool learning experience.

@CaptainCheezmo 10 жыл бұрын

Rottdog300 Lol, I wouldn't consider that the safest way of demonstrating something, but it sure must've gotten the point across well!