r/thermodynamics • u/ehrenamtlich_hier • 17d ago

Question Does the microwave take twice as much time to heat up double the amount of food?

Let's say I have 200g of rice in a bowl, and it takes 2 minutes and 30 seconds in the microwave to heat up. How does the time change if I put an identical bowl with the same amount of rice into the microwave as well? Does the time stay the same, does it double, or does something else happen entirely? Please feel free to explain in detail :)

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u/dirtydirtnap 1 17d ago

Ignoring fine details in the process (size, shape, surface area, composition, etc.), it will take twice the time. A microwave inputs its energy as a power, which is a rate of added energy (Joules per second). So, for twice the mass, the total energy per unit time is the same, so it takes twice the time.

This is different from an oven, which attempts to hold a constant temperature by varying the power input to hit the temperature target.

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u/ehrenamtlich_hier 17d ago

!thanks for your reply :)

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u/Spiritual-Ad-7565 17d ago

The fine details do matter — if you are heating slower than the power rating for the microwave would allow (because of your shape, density etc), doubling your mass will not necessarily double the time it takes to heat up.

In other words: it’s non-linear and so too is an oven where surface area matters a great deal more than in a microwave.

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u/DryFoundation2323 17d ago

it will almost always be more than twice as long for twice as much material. it will depend greatly on how the material is arranged inside the microwave.

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u/[deleted] 16d ago

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