The atoms and molecules ina gas are in constant motion.Temperature is a measure ofthe speed with which theymove. (More exactly it is ameasure of their averagekinetic energy.) The higherthe temperature, the fasterthe molecules move.
Measurement Of temperature:-Temperature can be measured by the following devices:- Mercury Thermometer Ideal Gas Thermometer Pyrometer Electrical Resistance Thermometer
PV = nRT (Macroscopic Form)Basically says that the state of a gas is also dependent on thenumber of particles in the sample of gas. So, by adding a termfor the number of moles of particles and proportionalityconstant “R” to the combined gas law, we get Ideal Gas Law. “n” is the number of moles of the gas. “R” the Universal Gas Constant is the same for all gases.
The heat capacity C of an object is the heat energy neededto raise its temperature by 1 kelvin (or 1 degree celsius).When different substances undergo the same temperaturechange they can store or release different amounts of heat.Something with high heat capacity heats up slower andcools down faster.Heat Capacity = Q / TQ – thermal energy (J)ΔT – temperature change (K)
Defined as the amount of thermal energy required to produceunit temperature rise in unit mass of the material.Unit mass isnormally 1kg, and unit temperature rise is normally 1KSpecific Heat Capacity = Q / (m T)Unit:-J kg-1 K-1,where m is the mass of the material
Calorimetry means measurement of heat.When a body athigher temperature is brought in contact with another body atlower temperature, the heat lost by the hot body is equal to theheat gained by the colder body, provided no heat is allowed toescape to the surroundings. A device in which heatmeasurement can be made is called a calorimeter.
The change of state from solid to liquid is called melting andfrom liquid to solid is called fusion. The temperature at whichthe solid and the liquid states of the substance in thermalequilibrium with each other is called its melting point.The melting point of a substance at standard atomsphericpressure is called its normal melting point.
Some important termsThe change of state from liquid to vapour (or gas) is calledvaporisation.The temperature at which the liquid and the vapour states ofthe substance coexist is called its boiling point.The boiling point of a substance at standard atmosphericpressure is called its normal boiling point.The change from solid state to vapour state without passingthrough the liquid state is called sublimation, and thesubstance is said to sublime.
The amount of heat per unit mass transferred during change ofstate of the substance is called latent heat of the substance forthe process.Q=mLWhere, Q is the heat required, m is the mass of the substance L is known as latent heatIts SI unit is J kg–1.The latent heat for a solidliquid state change is called thelatent heat of fusion (Lf), and that for a liquid-gas statechange is called the latent heat of vaporisation (Lv).
Conduction is the mechanism of transfer of heat between twoadjacent parts of a body because of their temperaturedifference. Gases are poor thermal conductors while liquidshave conductivities intermediate between solids and gases.Heat conduction may be described quantitatively as the timerate of heat flow in a material for a given temperaturedifference.
Convection is a mode of heat transfer by actualmotion of matter. It is possible only in fluids. Convection canbe natural or forced. In natural convection, gravity plays animportant part. Convection involves bulk transportof differentparts of the fluid. In forced convection, material is forced tomove by a pump or by some other physical means.
Conduction and convection require some Material as atransport medium. These modes Of heat transfer cannotoperate between bodies Separated by a distance in vacuum.But the Earth does receive heat from the sun across a Hugedistance and we quickly feel the warmth Of the fire nearbyeven though air conducts Poorly and before convection can setin. The Third mechanism for heat transfer needs noMedium; it is called radiation and the energy So radiated byelectromagnetic waves is called Radiant energy.The electromagnetic radiation emitted by a body by virtue ofits temperature like the radiation by a red hot iron or light froma filament lamp is called thermal radiation.
Newton’s Law of Cooling says that the rate of cooling of abody is proportional to theexcess temperature of the body over the surroundings: T(t) = TA + (TH-TA) e-kt where T(t) = Temperature at time t TA = Ambient temperature (temp of surroundings) TH = Temperature of hot object at time 0 k = positive constant t = time.