how does the thermos keep my tea hot for several hours?
In: 30
A thermos has two “walls” separated by a layer that has been evacuated (had all the air sucked out).
Vacuums are extremely bad at transferring heat because of the lack of particles; they can only do so by a process called radiation.
Imagine you are standing at the front of a classroom and want to give a book to someone at the back of the room. There are three ways to do this.
1) You can pass the book to the person next to you and have them do the same until it gets to the back. This is *conduction* – passing heat from particle to particle.
2) You can walk to the back of the room yourself (or someone else can). This is *convection* – the heat moves through a fluid but remains “attached” to one particle (there will then be some conduction transferring heat to different particles)
3) You can throw the book to the back of the room. This is *radiation* – heat transfer without using particles at all. It’s how the sun’s energy reaches earth.
Radiation is the least efficient of these three processes so by minimising conduction and convection the flask slows a change in the temperature of its contents.
Latest Answers