Thermos, like the Yeti, are used to keep hot liquids hot and cold liquids cold. Below is a diagram of a thermos. The diagram shows how a thermos works.

Question

Using the diagram and your knowledge of heat, which explanation is accurate about how the thermos works?

Question 23 options:

The reflective lining prevents heat loss by radiation, and the vacuum prevents heat loss by conduction.

The reflective lining prevents heat loss by conduction, and the vacuum prevents heat loss by radiation.

The reflective lining and the vacuum both prevent heat loss by conduction and radiation.

The reflective lining prevents heat loss by conduction and radiation, and the vacuum prevents heat loss by radiation only.

Answer 1

The accurate explanation about how a thermos works is:

The reflective lining prevents heat loss by radiation, and the vacuum prevents heat loss by conduction.

Here’s the reasoning:

• The reflective lining (often made of materials like silver) reflects heat radiation, which helps to keep hot liquids hot and prevent them from losing heat through radiation.
• The vacuum (the space between the two walls of the thermos) prevents heat transfer by conduction (and convection, though conduction is more directly relevant here) because there are no air molecules to conduct heat across the vacuum.

Thus, the first option accurately describes the functions of both the reflective lining and the vacuum in a thermos.