Is it bad to turn on a microwave if has nothing inside of be cooked?

Yes, it is generally not recommended to turn on a microwave if there is nothing inside of be cooked. This is because microwaves work by generating electromagnetic radiation, which can be harmful if it is not absorbed by food. When there is no food inside the microwave, the radiation can be reflected back into the magnetron, which can damage the microwave. Additionally, turning on a microwave with no food inside can create a fire hazard, as the energy from the radiation can cause flammable materials to ignite. Therefore, it is always best to place food in the microwave before turning it on.