Unit 4: Thermal Properties - Heat and Temperature

Vocabulary practice flashcards defining core terms, laws, principles, and concepts related to heat, temperature, thermal expansion, conduction, convection, and radiation.

Heat Energy

The sum of energies of all molecules of a body or system. It is an extensive property that flows from a body at higher temperature to one at lower temperature.

Temperature

The measure of the degree of hotness or coldness of a body or system, which reflects the average kinetic energy of its molecules and determines the direction of heat flow.

Absolute Zero Temperature

The theoretical temperature ($-273^\circ\text{C}$) at which the pressure and volume of a gas theoretically become zero, representing the minimum possible temperature for all gases.

Lower Fixed Point

The reference point on a temperature scale defined as the melting point of pure ice at normal pressure.

Upper Fixed Point

The reference point on a temperature scale defined as the boiling point of pure water at normal pressure.

Celsius Scale

A temperature scale suggested by Anders Celsius of Sweden in which the lower fixed point is $0^\circ\text{C}$ and the upper fixed point is $100^\circ\text{C}$, divided into $100$ equal parts.

Fahrenheit Scale

A temperature scale suggested by Fahrenheit of German where the lower fixed point is $32^\circ\text{F}$ and the upper fixed point is $212^\circ\text{F}$, divided into $180$ equal parts.

Kelvin Scale

A temperature scale developed by Kelvin where the lower fixed point is $273^\circ\text{K}$ and the upper fixed point is $373^\circ\text{K}$, divided into $100$ equal parts.

Conduction

The process by which heat is transferred from a part of a body at higher temperature to a part at lower temperature without the bodily movement of particles.

Variable State

The condition of a conducting body where its temperature continues to rise because the heat absorbed by the material is greater than the heat given out.

Steady State

The state of a conducting body where the temperature at each point remains constant over time because the heat absorbed by the material equals the heat given out.

Coefficient of Thermal Conductivity ($K$)

The amount of heat conducted per second in steady state through a unit cross-sectional area of a material of unit thickness with a unit temperature difference between its opposite faces.

Temperature Gradient

The change in temperature per unit length of a rod, given by $\frac{\theta_1 - \theta_2}{d}$ and measured in units of $^\circ\text{C}/\text{m}$ or $\text{K}/\text{m}$.

Coefficient of Linear Expansion ($\alpha$)

The change in length per unit original length per unit change in temperature of a solid rod, expressed as $\alpha = \frac{\Delta l}{l_0 \Delta T}$.

Coefficient of Superficial Expansion ($\beta$)

The change in surface area per unit original surface area per unit change in temperature of a solid material, defined by $\beta = \frac{\Delta S}{S_0 \Delta T}$.

Thermal Resistance ($R$)

A measure of a material's opposition to heat flow, which is inversely proportional to its thermal conductivity ($R \propto \frac{1}{K}$).

Thermometric Properties

The physical characteristics of any material that change uniformly with temperature and are utilized to measure temperature.

Thermometric Substances

Materials used for constructing thermometers, such as mercury, alcohol, gases, and platinum, characterized by properties like uniform expansion and high boiling point.

Convection

The process by which heat is transmitted through a substance from one point to another due to the bodily motion of heated particles.

Free Convection

A mode of convection that occurs naturally within a fluid that is initially at rest, such as trade winds or still air in a closed room.

Forced Convection

A mode of convection that takes place in a controlled, steady stream of fluid driven through another fluid, such as room cooling using an exhaust fan.

Radiation

The process of heat transmission in the form of electromagnetic waves from a body at higher temperature to one at lower temperature without heating the intervening medium.

Thermal Radiation

Heat energy emitted by a body solely by virtue of its temperature.