When you microwave two things in the microwave, the uneven heating can occur due to a combination of factors:
Composition and Density: The composition and density of the objects being microwaved can play a significant role in how they heat up. Microwaves work by emitting electromagnetic waves that are absorbed by water, fats, and certain other molecules present in food. Objects with higher water or fat content tend to heat up more quickly than those with lower content. For example, if one of the items has more water or fat molecules, it will heat up faster than the one with less.
Size and Shape: The size and shape of the objects also matter. Microwaves create standing waves inside the oven, leading to areas of high and low energy. Depending on how the objects are positioned in relation to these waves, one may receive more microwave energy and heat up faster than the other.
Positioning in the Microwave: Placing the items in different locations in the microwave can result in varying heating patterns. For instance, if one item is closer to the center of the microwave's turntable, it may receive more even exposure to the microwaves and heat up more consistently.
Microwave Power and Time: If one item requires more cooking time than the other, it might not have received sufficient heating when you take them out together. The microwave's power level and the cooking time set on the oven could impact the degree of heating each item experiences.
Thermal Conductivity: The objects' thermal conductivity (the ability to transfer heat) can also play a role. If one item is a good heat conductor, it may transfer some of its heat to the adjacent item, leading to uneven heating.
Stirring and Turning: In some cases, stirring or turning the food during the microwaving process can help distribute the heat more evenly.
Keep in mind that microwaves are not always the most uniform cooking devices, and uneven heating is a common issue. To achieve more consistent results when microwaving multiple items, consider using lower power settings and adjusting the cooking time as needed. Additionally, rearrange the items or turn them during cooking to promote more even heating.