Physics Ultimate Study Guide

Heat

A form of energy that flows from a body at a higher temperature to a body at a lower temperature when they are in thermal contact.

Thermal equilibrium

The state reached when two bodies in thermal contact attain the same temperature and heat flow stops.

Temperature

The degree of hotness or coldness of a body; it determines the direction of spontaneous heat flow.

Internal energy

The sum of the internal kinetic energy and internal potential energy of all molecules in a body.

Joule (J)

The SI unit of heat energy.

Calorie (cal)

The quantity of heat required to raise the temperature of $1\,\text{g}$ of pure water by $1\,^\circ\text{C}$.

Kilocalorie (kcal)

The quantity of heat required to raise the temperature of $1\,\text{kg}$ of pure water by $1\,^\circ\text{C}$; $1\,\text{kcal} = 1000\,\text{cal}$.

Mechanical equivalent of heat

Approximately $1\,\text{cal} \approx 4.2\,\text{J}$ (precisely $1\,\text{cal} = 4.186\,\text{J}$).

Degree Celsius ($^\circ\text{C}$)

A thermometer scale unit of temperature written as $^\circ\text{C}$, with ice point $0\,^\circ\text{C}$ and steam point $100\,^\circ\text{C}$.

Kelvin (K)

The SI unit of thermodynamic temperature, written as $\text{K}$ without a degree symbol.

Absolute zero

The lowest theoretical temperature, $0\,\text{K} = -273\,^\circ\text{C}$, at which all translational molecular motion ceases.

Thermometer

The instrument used to measure temperature, operating on the principle of uniform thermal expansion of liquids.

Lower fixed point (ice point)

The position of the mercury meniscus in a thermometer when the bulb is in pure melting ice at standard pressure, marked $0\,^\circ\text{C}$.

Upper fixed point (steam point)

The position of the mercury meniscus in a thermometer when the bulb is in steam from boiling water at standard pressure, marked $100\,^\circ\text{C}$.

Parallax error

The error caused by eye level not being aligned with the top of the mercury meniscus, avoided by horizontal line of sight.

Celsius to Fahrenheit conversion

The formula $F = \frac{9}{5} \times C + 32$ converts Celsius to Fahrenheit.

Celsius to Kelvin conversion

The formula $T\,\text{K} = (273 + t)\,\text{K}$ converts Celsius to Kelvin, where $t$ is in $^\circ\text{C}$.

Latent heat

The physical transformation at a constant temperature in which heat changes internal potential energy without changing temperature.

Melting (fusion)

Transition of a solid to liquid at a fixed melting point, such as ice melting at $0\,^\circ\text{C}$.

Vaporization (boiling)

Transition of a liquid to gas at a fixed boiling point, such as water to steam at $100\,^\circ\text{C}$.

Evaporation

Slow, silent, surface transition of liquid to vapour occurring at all temperatures.

Sublimation

Direct transition of a solid into gas upon heating without passing through the liquid phase, e.g., camphor or iodine.

Deposition

Direct transition of a gas into solid upon cooling without passing through the liquid phase.

Conduction

Heat transfer through a substance from molecule to molecule without bulk movement of particles, dominant in solids.

Convection

Heat transfer within fluids by actual displacement and circulation of heated particles, occurring vertically upward.

Radiation

Transfer of heat by electromagnetic waves directly from source to receiver, requiring no material medium and traveling at the speed of light.

Conductor of heat

A material that allows heat to flow through it rapidly with minimal resistance, such as metals like silver, copper, and aluminium.

Insulator (bad conductor) of heat

A material that impedes the flow of heat, such as wood, cork, wool, glass, or stationary air.

Linear expansion

Thermal expansion along the length of a solid.

Superficial expansion

Thermal expansion of a solid's surface area.

Cubical expansion

Thermal expansion of a substance's total volume.

Bimetallic strip

A strip made of two riveted metals with different expansion rates that bends when heated, used in thermostats.

Anomalous expansion of water

The anomalous behaviour of water between $0\,^\circ\text{C}$ and $4\,^\circ\text{C}$, where it contracts on heating and reaches maximum density at $4\,^\circ\text{C}$.

Thermos flask (Dewar flask)

A double-walled glass vessel with evacuated interspace and silvered walls that minimizes conduction, convection, and radiation to keep contents hot or cold.

Sea breeze

Warm, less dense air over land rising during the day and cooler sea air moving inland.

Land breeze

Air movement from land to sea at night caused by faster cooling of land than sea.

Good absorber of radiant heat

Surfaces such as dull black ones that absorb radiant heat more effectively than white or polished surfaces.