If a potato is placed on a pure white paper plate & put in microwave, the potato heats up but not the paper plate. Why?
A microwave heats food quickly because all foods contain significant amounts of water and water is a polar molecule. This means that every water molecule has one side that is relatively positive (the hydrogen atoms) and one side that is reliatvely negative - (the oxygen atom).The water readily absorbs the microwave energy and the increased energy causes the water to vibrate, heating up. The heated water in turn heats the surrounding food molecules and your food is ready to eat.
A paper plate contains very little moisture, and the molecules in the paper are not very polar in character so it does not easily absorb the microwave energy and so stays relatively cool.