He ! what’s the electromagnetic wave that has a wavelength between 1mm and 30cm

You've got some UHF radio waves at the long end of that range.  But most of the range consists of microwaves.

For example:  In the US, the "microwave oven" kitchen appliance cooks with radiation at a wavelength of about 12.2 cm .  

a long strand of spaghetti is folded once. if this is cut 20 times, how many pieces of spaghetti will there be? a long strand of spaghetti is folded once. if this is cut 20 times, how many pieces of spaghetti will there be? a long strand of spaghetti is folded once. if this is cut 20 times, how many pieces of spaghetti will there be? a long strand of spaghetti is folded once. if this is cut 20 times, how many pieces of spaghetti will there be? a long strand of spaghetti is folded once. if this is cut 20 times, how many pieces of spaghetti will there be?

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frequency or wavelenth of em radiation in a vacuum