Answer:
When an electric heater is used.
Step-by-step explanation:
A possible scenario would be the use of an electric heater, where electric power is transformed into thermal energy that will increase the temperature of a room.
The Law of Conservation of Energy states that energy can not be created nor destroyed, it can only be transformed or transferred from one form of energy to another. If we apply this law to our scenario we can appreciate that the electric power is transformed in a different type of energy known as thermal energy.