Why does the time to microwave something increase when the quantity of the item increases?

Question

If i put in 1 individual cookie in the microwave it takes like 15 seconds to get heated and melted, but if i put two, then it isnt as warm and melted at 15 seconds. Why does it matter if there is an extra cookie on the plate? its not adding to the first cookie or anything.

Just wondering.

Answer 1

Vidigod is spot on, but I wanted to point out that the first answer is dead wrong. It's a "Old wives tale" that food cooks for x seconds after the microwave stops. There is NO additional energy being put into the food once the microwave emitter is turned off, as Vidogod's answer would also suggest.

What does happen is that some areas of the food are hotter than others because wetter areas tend to catch more microwave energy, and the emitters don't hit all parts of the food equally either. The heat energy in the hotter areas is shared with the cooler areas, even once the oven is off. This is through a more conventional process called convection. The food is not still "cooking", just evening out the heat.

By the same token, when you pick up the hot cookie and it feels warm, you are not "still cooking" your fingers, you are just transmitting heat from the cookie to your fingers through convection.

Answer 2

Well, I'm no expert in this field, but I have a good idea as to why this may be case. Maybe somebody else can back me up on this.

A microwave emits radiation (inside the microwave and hopefully not outside). Radiation is nothing more than light (which you can't see because it is not in the visible part of the spectrum). The basic unit of light is the photon. The microwave emits a certain number of photons. The photons bounce around in the microwave until they are absorbed by the atoms in your food. In absorbing the photon, the atoms gain more energy, move around more, and thus your food becomes more heated.

The more food you have in a microwave, the more atoms that need to absorb a photon for heating. A microwave only produces a certain number of photons at a time, so, in 15 secs, the same number of photons are being used to heat up twice as many atoms (since you are heating two cookies instead of one). To heat both cookies up to the same degree, you will need to heat longer (though not necessarily twice as long).

Why not twice as long? Well, I'm not a expert...

Hope this helps.

Answer 3

the absorbsion rate changes with increased mass in the oven

by the way - microwaved food keeps cooking for 25% longer than you put it in for

so if you placed it in for 60 seconds - it will actually cook for 75!
even though you take it out of the microwave!