what is the application of electric dipole in a microwave oven?

Food has a high percentage of water and other polarised molecules. Polarised molecules (which behave as electric dipole) try to line themselves up with the electrical field inside the oven, like compass needles trying to point at North.

But because the electrical field is changing 2,450 million times a second the molecules don't quite have time to line up one way before they have to try to line up the other way.

So, anything with water in it has all these molecules being moved this way and that by the electrical field gets heated up.