15 terms

# Conceptual Physics--Chapter 22 Heat Transfer

Conceptual Physics 10th e. by Paul G. Hewitt Summary of Terms, Summary of Formulas, and Terms Within the Textbook

#### Terms in this set (...)

Conduction
The transfer of heat energy by molecular and electron collisions within a substance (especially a solid).
Convection
The transfer of heat energy in a gas or liquid by means of currents in the heated fluid. The fluid moves, carrying energy with it.
The transfer of energy by means of electromagnetic waves.

²Note:* The radiation we are talking about here is electromagnetic radiation, including visible light. Don't confuse this with radioactivity, a process of the atomic nucleus that we'll discuss in Part 7.
The radiation emitted by the Earth to outer space.
Newton's law of cooling
The rate of loss of heat from an object is proportional to the temperature difference between the object and its surroundings.
Greenhouse effect
Warming of the lower atmosphere by short-wavelength radiation from the Sun that penetrates the atmosphere, is absorbed by the Earth, and is reradiated at longer wavelengths that cannot easily escape Earth's atmosphere.
Solar constant
1400 J/m² received from the Sun each second at the top of Earth's atmosphere on an area perpendicular to the Sun's rays; expressed in terms of power, 1.4 kW/m².
Solar power
Energy per unit time derived from the Sun.
Insulator
(a) Material that is a poor conductor of heat and that delays the transfer of heat.
(b) Material that is a poor conductor of electricity.
Any energy, including heat, light, and X rays, that is transmitted by radiation. It occurs in the form of electromagnetic waves.
Electromagnetic wave
Energy-carrying wave emitted by vibrating charges (often electrons) that is composed of oscillating electric and magnetic fields that regenerate one another. Radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X rays, and gamma rays are all composed of electromagnetic waves.
Frequency
For a vibrating body or medium, the number of vibrations per unit of time. For a wave, the number of crests that pass a particular point per unit time. Frequency is measured in hertz.
The rate of cooling of an object--whether by conduction, convection, or radiation--is approximately proportional to the temperature difference ∆T between the object and its surroundings.
Rate of cooling ~ ∆T
This is known as Newton's law of cooling.
*Newton's law of cooling*
The law holds also for warming. If an object is cooler than its surroundings, its rate of warming up is also proportional to ∆T.*⁴* Frozen food will warm up faster in a warm room than in a cold room.
A warm object that contains a sourcee* of energy may remain warmer than its surroundings indefinitely. The heat it emits doesn't necessarily cool it, and Newton's law of cooling doesn't apply. Thus, an automobile engine that is running remains warmer than the automobile's body and the surrounding air. But, after the engine is shut off, it cools in accordance with Newton's law of cooling and gradually approaches the same temperature as its surroundings. Likewise, the Sun will remain hotter than its surroundings as long as its nuclear furnace is running--give it five billion years or so.