In a microwave oven, the food is kept in a plastic container and the microwave is directed towards the food. The food is cooked without melting or igniting the plastic container. Explain.

The food which is being cooked contains water. The microwaves which are directed towards the food has a natural frequency that match with the frequency of water. The water molecules inside the food absorb energy from the microwaves and get heated up causing the food around it to heat up. Due to absorption of energy of the microwaves, the food gets cooked. Whereas the plastic does not have any water molecules which would absorb energy and the frequency also doesn’t match with the natural frequency of the microwaves so the plastic container remains unaffected.