Heat transfer：練習問題

Which of the following is the most important reason why air is a very poor thermal conductor?

How does the density of water change when it is heated from \(20^{\circ}\text{C}\) to \(60^{\circ}\text{C}\), and how does this lead to a convection current?

A refrigerator is designed to keep its contents cool. Which features of a refrigerator primarily reduce heat transfer from the surroundings to the inside?

When a student holds a short copper rod in a Bunsen flame, they quickly feel the heat. According to the particle theory, how is the thermal energy transferred through the rod?

Which of the following statements correctly explains why trapped air (such as in a wool sweater or fiberglass insulation) is such an effective thermal insulator?

Which mode of heat transfer allows thermal energy from the Sun to reach the Earth through the vacuum of space?

In a room with a heater, explain why the heater is usually placed near the floor rather than near the ceiling to warm the entire room effectively.

An experiment is conducted where identical wax discs are placed on two surfaces at room temperature: one silver and one styrofoam. The silver surface feels significantly colder, but the wax on it melts at a much higher rate. Explain this observation by discussing the conductive properties of the materials and the energy transfer involved.

A vacuum flask (thermos) is an everyday object used to store hot or cold drinks.
(a)<\/b> The flask features a double-walled glass container with a vacuum in the space between the walls. Which two<\/b> modes of heat transfer are prevented by this vacuum? (1 point)
(b)<\/b> Explain, in terms of particles, why a vacuum is such an effective insulator against convection. (2 points)
(c)<\/b> Which mode of heat transfer can still travel across the vacuum space? (1 point)<\/p>

A student uses a "convection box" to study the movement of air. The box is sealed with a glass front and has two chimneys, X and Y, on the top. A lit candle is placed inside the box directly under chimney X, and a piece of smouldering paper (which releases visible smoke) is held over the top of chimney Y.