Microwave cooking

This is just a little curiosity I've had, and I wonder what y'all think:

I am poaching a chicken egg in a small (about 4 in. diameter) glass dish in my microwave. Let's assume the microwave is set on a medium level of heat intensity that is held constant throughout heating (I'm not sure if that's a reasonable assumption).

Here's the quandary: suppose I run two separate experiments. In the first experiment, I poach a single egg in the microwave for some time, $$t$$. In the second experiment, I simultaneously poach two eggs (each in its own dish) for the same amount of time, $$t$$. The glass dishes are essentially identical.

Will the eggs in the two experiments reach the same temperature?

In practice, it seems that when there are two eggs (each in its own dish) being microwaved they each obtain a lower temperature than the single egg alone in the microwave. Is that an expected result?

• It is true for potatoes too, about 5 minutes per potato for baked ones in the microwave. It is because the energy provided by the microwaves is divided to the existing mass: waves absorbed by one are not available to the others. I've done up to 7 in a covered pyrex bowl. Nov 24 '18 at 18:25
• Interesting! That's what i thought, but I had a lingering doubt in my mind. Thank you, Anna Nov 24 '18 at 19:21

1 Answer

Yes, that is what you'd expect. Think of the magnetron pumping out photons at a set rate. Imagine that the walls of the box are perfectly reflective. Each photon bounces around inside the box until it gets absorbed by the food. With a small amount of food, it takes more bounces on average for a given photon to be absorbed, but in steady state, one photon must be absorbed for every photon emitted: all the energy coming out of the magnetron goes into the food. Double the food, and the temperature would be expected to increase half as quickly.

• Thank you for your answer. For clarity, what do you precisely mean by "but in steady state"? Do you mean that the net flux of photons through some tiny volume within the box is zero (as many entering as leaving)? Nov 24 '18 at 19:21
• I'm thinking of the box as a whole: if the magnetron is emitting more than the food is absorbing, the number of photons in the box is increasing; that's not steady state. Nov 24 '18 at 19:22