How do toasters work???

[Jaepheth]

Ok, so how does a microwave brown things? I can put something in a cardboard box with reflective paint and get out a browned hot pocket or browned sandwich. How?

I believe the metallic paint radiates enough heat to mimic an actual oven, but not enough to catch fire like aluminum foil would.

 

[Born2bwire]

I believe the metallic paint radiates enough heat to mimic an actual oven, but not enough to catch fire like aluminum foil would.

Yeah that would be my guess. When the microwaves strike the conductive material on the crisper they excite currents along the surface. If the conductive material has enough resistive value to it, these currents will quickly lose their energy in the form of heat (as opposed to just reradiating the energy away as a reflected microwave like the walls of the oven).

 

[zinfamous]

I believe the metallic paint radiates enough heat to mimic an actual oven, but not enough to catch fire like aluminum foil would.

correct me if I'm wrong, but the issue with metal in microwave is about non-smooth surfaces. aluminum foil is a problem because there will almost always be a wrinkle somewhere in there, which will initiate a spark.

In theory, a perfectly smooth piece of metal (I think some spoons have been shown to be OK?) will be fine. Forks are bad because of the prongs.

 

[Born2bwire]

correct me if I'm wrong, but the issue with metal in microwave is about non-smooth surfaces. aluminum foil is a problem because there will almost always be a wrinkle somewhere in there, which will initiate a spark.

In theory, a perfectly smooth piece of metal (I think some spoons have been shown to be OK?) will be fine. Forks are bad because of the prongs.

Sharp points give rise to an effect known as field enhancement where the electromagnetic fields become much higher in the close vicinity of these sharp points. This allows for high voltages between adjacent sharp points that can cause air to experience dielectric breakdown, the sparks that jump about.

 

[Farmer]

Sharp points give rise to an effect known as field enhancement where the electromagnetic fields become much higher in the close vicinity of these sharp points. This allows for high voltages between adjacent sharp points that can cause air to experience dielectric breakdown, the sparks that jump about.

Wow, exactly. Very good.

 

[lxskllr]

Who still uses Pentium IVs?

Hello. Typing this on a P4 2.8ghz Northy :^)

 

[slag]

Hello. Typing this on a P4 2.8ghz Northy :^)

Is it hot enough to toast bread?

 

[lxskllr]

Is it hot enough to toast bread?

Nah, That's Prescott :^D

 

[frostedflakes]

Ahahah

 

[HeXen]

I'm really tempted to make a parody thread right now.

 

[Rubycon]

You can make a lot of things glow red if you've got enough voltage to push those amps through.

Indeed. :biggrin:

Of course this also would make the wiring in your walls toast too. (barring proper oc protection)

If a nichrome element shorts out it will glow much brighter and this depends on how close it is to the opposing phase. You've probably seen the videos of the burning oven elements. That's precisely what happens when the inner wire makes contact with the grounded sheath.

The elements (in stove/ovens) are definitely NOT a solid piece of wire with high resistance. While the idea sounds neat and simple (for free air heating) the wire would have to suspended with insulators and could you imagine what would happen when a steel/copper/sstl pot/skillet were placed on that coil? :biggrin:

 

[OCNewbie]

http://www.howstuffworks.com/toaster.htm

perfect, thanks!

 

[Fenixgoon]

In steady state, the net radiation emitted from the wires can be used to describe its temperature. Maybe a way to say that is, nature already accounts for these effects if you turn the toaster on for an appreciable amount of time.



I'd also question the physics of that claim. I'm assuming you are using Wien's displacement law and backing out a temperature from the wavelength associated with orange light? Your math is a little off since I get around 5000K (about the surface temp of the Sun, 20,000K would get you in the UV). This would be correct if you assume that 1.) the object in question is a blackbody and 2.) orange is actually its spectral emissive peak. But 1.) your wire is not a blackbody and 2.) just because the wires appear to glow orange to your eyes does not mean its blackbody peak emission wavelength is exactly orange (or even in the visible, it is most likely in the infrared, as with most commonly occurring things on Earth). Technically you would need some detector that can find the emitted power as a function of wavelength, and scan through the appropriate range of wavelengths. In other words, your eye is not a good detector for characterizing the temperature of a surface via this type of thermal radiation detection.

And I think to respond to the OP, as many have said, It is a "short," per se, since you have current running through a fairly good conductor. You can't have an ideal "short" unless you have a superconductor. But in this case, your application is to generate heat via Joule heating. So you run high current through high effective resistance. What is the problem?

You can approximate any electronic configuration as an ideal linear (i.e., LRC or higher related derivatives) circuit, the correctness of the approximation depending on the situation. In this case, the current flow through any wire can be well approximated by some choice values of R, L, C, or higher derivative terms. In the ideal short would then mean infinite current which means, if the circuit is undriven, it lasts an infinitesimal amount of time, as the potential would equalize immediately, this is the limit of the ideal conductor.

i just did:

hc/lambda ~ kT

usually that gets you decently close. an order of magnitude off seems odd. DAMN YOU BOLTZMANN! hence why i said i knew ~20,000K wasnt right

 

[Jeff7]

i just did:

hc/lambda ~ kT

usually that gets you decently close. an order of magnitude off seems odd. DAMN YOU BOLTZMANN! hence why i said i knew ~20,000K wasnt right

And I'm pretty sure that even diamond would liquefy long before reaching that temperature, and possibly reach boiling too.



Checking:...ok, I was wrong. It would simply sublimate at 3900K. I think you need a new toaster. And some more bread, I think yours was vaporized.

 

[Farmer]

i just did:

hc/lambda ~ kT

usually that gets you decently close. an order of magnitude off seems odd. DAMN YOU BOLTZMANN! hence why i said i knew ~20,000K wasnt right

No you're right. I mean it was only factor of 4, because there is some factor there to account for fine detail of Planck distribution.

 

[SonicIce]

If a nichrome element shorts out it will glow much brighter and this depends on how close it is to the opposing phase. You've probably seen the videos of the burning oven elements. That's precisely what happens when the inner wire makes contact with the grounded sheath.

The elements (in stove/ovens) are definitely NOT a solid piece of wire with high resistance. While the idea sounds neat and simple (for free air heating) the wire would have to suspended with insulators and could you imagine what would happen when a steel/copper/sstl pot/skillet were placed on that coil? :biggrin:

so a toaster wire has an inner element like an oven does? can you get shocked by touching a toaster wire or sticking a butter knife in it while it's on?

 

[Rubycon]

so a toaster wire has an inner element like an oven does? can you get shocked by touching a toaster wire or sticking a butter knife in it while it's on?

No, the toaster element is the discrete wire. Why would you stick a knife in the toaster with it plugged in???!

 

[Jeff7]

No, the toaster element is the discrete wire. Why would you stick a knife in the toaster with it plugged in???!

The butter would certainly melt better that way.

:hmm:

 

[warr666]

.....

 

[Fenixgoon]

No, the toaster element is the discrete wire. Why would you stick a knife in the toaster with it plugged in???!

why would someone stick a fork or other metal bit in an electrical outlet? hehe

 

[zinfamous]

why would someone stick a fork or other metal bit in an electrical outlet? hehe

one of my physics professors in college decided to become a physicist at the age of 8--the day he jammed a fork into a wall socket.

 

[SonicIce]

No, the toaster element is the discrete wire. Why would you stick a knife in the toaster with it plugged in???!

so you'll get shocked? what if its plugged in but not turned on?

 

[Rubycon]

so you'll get shocked? what if its plugged in but not turned on?

Switches are supposed to break the hot wire and all modern plugs are polarized to prevent the obvious from happening but...

The real obvious thing is if you must insert a conductive object in a toaster you should unplug it from the wall.

If you need to change the blade on a saber saw you unplug it from the wall...

Well you should.

 

[Baked]

All I know is I put the bagel in the toaster, and deliciousness comes out. All this science stuff is tripping me out.

 

[SlitheryDee]

No, the toaster element is the discrete wire. Why would you stick a knife in the toaster with it plugged in???!

To see if what you think would happen, would happen?