Appliances that produce heat contain special metal wires called nichrome wires. Electricity does not flow easily in nichrome wires. When electricity is forced to flow in nichrome wires, lots of heat is produced. Electricity flows when very tiny electric particles called electrons move among other small particles called atoms and molecules. But when these electrons try to move in a nichrome wire, where electricity does not flow easily, the electrons smash into the atoms and molecules in the nichrome wire. The energy produced when these collisions happen creates heat. So this is how toasters and irons get hot.