A thermos cup, also known as a vacuum flask, is a type of insulated container that is used to keep beverages hot or cold for an extended period. The principle behind its working is based on the concept of thermodynamics.

The thermos cup consists of two layers of glass or plastic, with a vacuum in between them. The vacuum serves as an insulator and prevents heat from escaping or entering the container. The inner layer of the cup is coated with a reflective material, which reflects the heat back into the container, further reducing heat loss.

When you pour a hot beverage into a thermos cup, the heat energy from the beverage is transferred to the inner layer of the cup. The reflective coating then reflects this heat energy back into the beverage, minimizing heat loss. The vacuum between the two layers of the cup acts as a barrier and prevents heat from escaping, so the beverage remains hot for an extended period.

On the other hand, when you pour a cold beverage into a thermos cup, the same principle applies. The vacuum between the two layers of the cup acts as an insulator and prevents heat from entering, keeping the beverage cold.

In addition to the vacuum insulation, some thermos cups have additional insulation layers such as foam, to further improve their insulating properties. This makes them even more effective at keeping beverages hot or cold for longer periods.

In conclusion, the thermos cup works by minimizing heat transfer between the beverage and the environment using vacuum insulation and reflective coating. This makes it an excellent choice for keeping your beverages hot or cold for extended periods, making it an ideal choice for outdoor activities or long trips.