How does a microwave actually heat food so fast?

Microwaves heat food quickly because they use electromagnetic radiation at around 2.45 gigahertz, a frequency that causes water molecules to rapidly rotate and realign with the alternating electric field. This molecular friction generates heat throughout the food simultaneously, rather than relying on conduction from an outside heat source working its way inward like a conventional oven. The speed comes from this volumetric heating effect. Instead of waiting for heat to slowly transfer from a hot surface into the food's interior, the microwaves penetrate several centimeters into the food and agitate water molecules throughout that depth all at once. Foods with higher water content heat faster for this reason, while drier foods or materials like ceramic absorb very little microwave energy and stay relatively cool.