Social studies: Microwave

Percy Spencer was a building magnetrons (devices that produce microwaves) for radar sets with the company Raytheon. One time while experimenting with magnetrons the chocolate bar in his pocket melted.

The first food to be deliberately cooked with Spencer's microwave was popcorn, and the second was an egg, which exploded in the face of one of the experimenters. To verify his theory, Spencer created a high density electromagnetic field by feeding microwave power into a metal box from which it had no way to escape. When food was placed in the box with the microwave energy, the temperature of the food rose rapidly.

Thus the microwave oven was born.

Sources:
Wikipedia