I noticed that my tea tends to be much hotter when I microwave it continuously than when I take it out half-way through. This result seems to be consistent regardless of material. Even if I open the microwave just for a quick second, whatever I’m microwaving needs significantly more time to heat. Why is this?
In: Physics
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The magnetron inside your microwave that generates the microwaves is a vacuum tube, and the cathode inside it has to warm up before it starts emitting electrons. (literally warm up, as in temperature)
You will usually be able to hear a difference in the noise it makes a few seconds after you start it, this is when it’s really starting to work.
Microwaves work by agitating water molecules (heat after all is just agitated molecules). However, not all water molecules are agitated at the same time – as the waves don’t blanket the entire inside the entire time.
So, think of your glass of water as bunch of swings. You are the microwave. As you push a seat it starts to swing, then you run to the next one and push it, then the next. But, as you get away from the first one, it starts to slow down a bit. Now, if you add in a short break at the end, that first swing will slow down even more. To add to this, imagine you can only push the swing a little bit each time – if you can get back to the first swing while it’s still moving, your push will make it go faster each time you get to it.
The swings in this case are the water molecules – and by stopping the microwave, you’re giving a chance for them to slow down a bit.
Pro-tip: Most microwaves have a “Power Level” button where you can set the microwave to 40% to 100%. This doesn’t actually change how powerful the microwave is – it shuts the heating element off for 60% of the time to 0% (roughly). So, if you’ve ever tried to make nachos in the microwave and found it doesn’t melt the cheese evenly – try setting it to 50% and doubling the time.
The heating element in your microwave takes up to ten seconds to get to full power, and you’ll want to leave the door closed for a few seconds after it beeps to give the element time to cool down and stop sending radiation everywhere.
Also, microwaves typically have hot spots and cold spots, and if your drink doesn’t stumble into a hot spot, while the heating element is hot, during its time in the box, it will be much colder because it absorbed less energy.
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