Faraday cage

Faraday cage is usually shown as a confirmation that electric fields do not spread into a space enclosed by a sufficiently dense metal mesh. A microwave oven is also a cage by its structure, but it serves to prevent non-ionizing electromagnetic radiation from "escaping" outside and injuring people nearby with its thermal effect. A microwave oven can be used for a simple experiment if we put a wire cage in it with a glass of water. Place another glass in the oven outside the cage. The turned-on oven will bring the water in that glass to a boil, while the water in the cage will remain cold.
Note: Do not put the cage in the oven without an external glass of water. The water in the external glass will absorb the radiation and there will be no sparks on the metal mesh of the cage.