glennmac
Veteran Member
Grog,
I'm happy to report that the Web does know what causes electricity. And it happens to be the very same thing that causes fire . . . . . CARROTS:
<font color=blue>Icy Sparks from your Carrots !!
If you often cook mixed vegetables from frozen in a microwave, on a microwaveable plate you may notice that carrots produce sparks during cooking and, on closer examination, they display small burns. Why is this? several factors make frozen carrots susceptible to the effect described (although other vegetables do this).
First, while microwaves are extremely good at heating liquid water, ice is almost totally transparent to them, so it is actually quite difficult to get ice to melt in a domestic microwave oven. The "defrost" option on a microwave oven relies on intermittent heating of a small amount of liquid water present on the food, and heat conduction from these areas into frozen material. By putting frozen material into the microwave oven with continuous energy input, no time is given for thermal conductivity effects, and therefore a colossal heating effect occurs on a very localised surface area. These areas, typically at the extreme point of the carrot, will dry out rapidly and then char, essentially forming small carbon points.
Secondly, carrots are relatively large objects (compared to, say frozen peas) and because microwaves are essentially varying high voltage fields, a large alternating electrical potential exists between the highly conductive charred sections.
Thirdly, carrots are generally given quite angular cuts, giving sharp points which will yield the highest field gradients. The combination of a large alternating field across a good electrical conductor with sharp points causes electrical breakdown of the air and the sparks which accompany this. Depending upon the precise conditions, it is equally possible for charring to be a secondary effect, rather than a cause. In this case, the discharge may originate from uncharred points, with charring only occurring as a huge current passes through a relatively small point.</font color=blue>
I'm happy to report that the Web does know what causes electricity. And it happens to be the very same thing that causes fire . . . . . CARROTS:
<font color=blue>Icy Sparks from your Carrots !!
If you often cook mixed vegetables from frozen in a microwave, on a microwaveable plate you may notice that carrots produce sparks during cooking and, on closer examination, they display small burns. Why is this? several factors make frozen carrots susceptible to the effect described (although other vegetables do this).
First, while microwaves are extremely good at heating liquid water, ice is almost totally transparent to them, so it is actually quite difficult to get ice to melt in a domestic microwave oven. The "defrost" option on a microwave oven relies on intermittent heating of a small amount of liquid water present on the food, and heat conduction from these areas into frozen material. By putting frozen material into the microwave oven with continuous energy input, no time is given for thermal conductivity effects, and therefore a colossal heating effect occurs on a very localised surface area. These areas, typically at the extreme point of the carrot, will dry out rapidly and then char, essentially forming small carbon points.
Secondly, carrots are relatively large objects (compared to, say frozen peas) and because microwaves are essentially varying high voltage fields, a large alternating electrical potential exists between the highly conductive charred sections.
Thirdly, carrots are generally given quite angular cuts, giving sharp points which will yield the highest field gradients. The combination of a large alternating field across a good electrical conductor with sharp points causes electrical breakdown of the air and the sparks which accompany this. Depending upon the precise conditions, it is equally possible for charring to be a secondary effect, rather than a cause. In this case, the discharge may originate from uncharred points, with charring only occurring as a huge current passes through a relatively small point.</font color=blue>