Invention of the microwave oven: Chocolate bar anecdote

[greypilgrim]

Hi.

I've just read that microwave ovens were invented 75 years ago. The article mentions the following anecdote: Apparently, Percy Spencer discovered the heating effect of microwave radiation when a magnetron nearby melted a chocolate bar in his pocket. Is this story plausible, wouldn't you feel the effect of radiation of such power much earlier in your own tissue, maybe even at dangerous levels?

 

[berkeman]

Hi.

I've just read that microwave ovens were invented 75 years ago. The article mentions the following anecdote: Apparently, Percy Spencer discovered the heating effect of microwave radiation when a magnetron nearby melted a chocolate bar in his pocket. Is this story plausible, wouldn't you feel the effect of radiation of such power much earlier in your own tissue, maybe even at dangerous levels?

Link to the article? The Wikipedia biography does not seem to mention it...?

 

[greypilgrim]

Yes it does, in the second paragraph of the "Career" section. The microwave oven article mentions it as well.

 

[berkeman]

Yes it does, in the second paragraph of the "Career" section. The microwave oven article mentions it as well.

Ah, thanks. I searched on your words "chocolate bar" and got no hits in the article. It calls it a "candy bar", okie dokie.

Yeah, he must have felt at least a bit warm standing in front of a transmitting radar antenna, but I do wonder why the candy bar melted before he became uncomfortable. I wonder it he had any kids before this work...

 

[phinds]

Ah, thanks. I searched on your words "chocolate bar" and got no hits in the article. It calls it a "candy bar", okie dokie.

Yeah, he must have felt at least a bit warm standing in front of a transmitting radar antenna, but I do wonder why the candy bar melted before he became uncomfortable. I wonder it he had any kids before this work...

I think chocolate is particularly susceptible to microwave warming so that might explain it.

 

[Baluncore]

The melting point of the best chocolate is close to body temperature. I expect the chocolate was wrapped in waxed paper at that time, not in foil.

Most of the human body has blood circulation that transports local heat throughout the body.

The human body has greater water content and so may reflect microwaves differently to chocolate. That may have been a function of the unspecified? Raytheon radar frequency.

People prefer to work where they are comfortable. In cold weather, factory workers would compete to operate RF diathermy machines.

 

[tech99]

From my recollection of the patent, it is noticeable that it gives great details about the circuit of a push-puill magnetron oscillator, but less about the concept of microwave heating. I think this illustrates the shift from thinking of components to systems which has happened over the past 70 years.

 

[DrClaude]

Apparently, it was not a chocolate bar, but a peanut cluster bar, which has a higher melting point
https://www.popularmechanics.com/te...7/how-the-microwave-was-invented-by-accident/

I am very skeptical that the story is true as it is told. I can't believe that the candy bar was in his pocket when this happened.

 

[Rive]

Well, according to wiki, the radar devices that time was in the range up to 10-20kW and the frequency was already measured in GHz. I did think it was lower.

I think we can safely assume that in the story it was about some stray radiation and not the main beam... And I would still think that some tin foil wrap was involved.

 

[phinds]

I think we can safely assume that in the story it was about some stray radiation and not the main beam... And I would still think that some tin foil wrap was involved.

I'm pretty sure than tin foil wrap was not used for candy bars that far back.

 

[Dullard]

Lots of people 'discovered' that effect prior to microwave ovens. I knew an individual (now deceased) who intentionally warmed his hands in front of a microwave dish.

 

[Rive]

I'm pretty sure than tin foil wrap was not used for candy bars that far back.

Well. Can't tell how common it was, but Kit Kat definitely had tin foil wraps. I could also found references for Hershey's_Kisses, gum wraps and some more. Also found references for collecting (all kind) of foil wraps as homefront effort.
I'm not a historical, though.

 

[phinds]

Lots of people 'discovered' that effect prior to microwave ovens. I knew an individual (now deceased) who intentionally warmed his hands in front of a microwave dish.

Are the two facts related

 

[russ_watters]

I am very skeptical that the story is true as it is told. I can't believe that the candy bar was in his pocket when this happened.

Why? What seems implausible about that?

 

[DrClaude]

Why? What seems implausible about that?

It is hard for me to see how he could discover the melted candy bar without feeling any heat from the radar.

 

[russ_watters]

It is hard for me to see how he could discover the melted candy bar without feeling any heat from the radar.

Ok, fair enough. I'm not sure what the melting temp of that candy bar was or the energy absorption you get from standing near a radar. My only basis of comparison/contrast is with a standard electric or gas radiant heater, which is high temperature ir. I would think, but don't know, that the heating you'd get from microwaves would be subtle because you are more directly heating inside with a low temperature rise vs the skin with a high temperature rise. For example with ir you can still feel cold inside despite standing in front of a campfire and feeling the radiant heat on your skin. I imagine microwaves being like feeling warm after walking up some stairs except that you didn't just walk up stairs.

But that's just speculation.

 

[Baluncore]

The heat accumulates in the thermally insulated candy bar. A similar amount of heat appears in the similar near surface volumes of the body around the candy bar.

But the circulatory system transfers that heat throughout the body, so the local temperature of the body does not rise as fast as the candy bar.

The skin on the surface of the body, where the temperature sensors are located, is cooled by the air.

Would you notice the slight local heating while you are distracted by the hotter candy bar in your pocket?

 

[phinds]

It is hard for me to see how he could discover the melted candy bar without feeling any heat from the radar.

Well, remember, a Hershey's chocolate bar will melt in your shirt pocket and you won't feel any extra heat.

 

[DaveC426913]

It is hard for me to see how he could discover the melted candy bar without feeling any heat from the radar.

I don't find it implausible. Anyone used to working around any kind of machinery will be aware of the heat they give off. Even my laptop warms my legs quite noticeably, but it's so mundane, it doesn't even rise the level of conscious awareness. It's easy to understand how he would think nothing of the warmth.