1. Sun: It is the primary source of light and it gives us light and heat.
2. Combustion: Heat energy can be generated by the burning of fuels like wood, Kerosene, Coal, Charcoal, Petrol etc.
3. Friction: We can generate heat by rubbing two surfaces of some substances. In the past people used to rub two stones together to light fire.
4. Electricity: When Electric current flows through a conductor, heat energy is produced. Ex.: Iron box, Electric kettle.