Energy carried by electromagnetic waves
Like sound waves, electromagnetic waves have energy carried by the electric and magnetic fields that comprise the wave. It is due to this energy that, microwaves, for example can warm or cook food. In a microwave oven, the waves pass through the food and transfer their energy to it, which causes it to heat and cook. The electric field of microwaves is largely responsible for delivering the energy because water, which is in most foods, readily absorbs it. Water absorbs microwaves easily because water molecules have a permanent dipole moment. This means that one side of the water molecule has a slight positive charge and the other has a complementary negative charge. The rapidly oscillating electric field caused by the microwave causes the water molecule to spin at a high rate, which in turn causes it to heat up quickly. And because microwaves can penetrate all parts of the food, it causes uniform heating of the food.
Click here for a java applet demonstrating an electromagnetic wave propagating.
