Why water contained in a glass cup is warmed quickly in a microwave oven while the glass cup itself warms much more slowly?

Answer 1

The microwave does exactly what it says on the tin and cooks food by emitting microwaves. These microwave energy causes the vibration of other molecules, most commonly the water in foods. As the molecules vibrate they give off energy as heat, thus heating the food or liquid. The water molecules can easily vibrate because they are liquid and can move around more freezely. The molecules of the glass are held very rigidly in place. Thus they cannot vibrate anywhere near as much as the water molecules and so the glass does not heat up. Most of the warmth of the glass itself is actually heat that has transferred from the water, not the microwave energy. If you put a an empty cup into the microwave for the same amount of time as a cup of water, you will find that the empty cup does not heat up. Hope this helps, any corrections to my answer are welcomed in the name of science!