Students can go through AP Inter 1st Year Physics Notes 12th Lesson Thermal Properties of Matter will help students in revising the entire concepts quickly.
AP Inter 1st Year Physics Notes 12th Lesson Thermal Properties of Matter
→ Temperature is a relative measure indicating the degree of hotness (or) coldness of a body.
→ Temperature is a macroscopic property of a body (or) system. It is a scalar quantity.
→ Heat is a form of energy transferred between two sys-tems by virtue of temperature difference.
→ The instrument used to measure temperature is called thermometer.
→ Relation between Celsius, Fahremheit, Reasumer and Kelvin Scales is \(\frac{c-0}{100}=\frac{F-32}{180}=\frac{R-0}{80}=\frac{K-273}{100}\)
→ The atoms are arranged in regular order in the form of a lattice in solids.
→ The interatomic force of attraction depends on the dis-tance between them.
→ As the temperature increases, the amplitudes of the vibrations of the atoms increases.
→ When a solid is heated its length, area and volume increase.
→ The increase in length, per unit length, per 1°C rise of temperature is called, the coefficient of linear expansion
αl = \(\frac{\Delta l}{l \times \Delta \mathrm{T}} /{ }^{\circ} \mathrm{C}\)
→ The increase in area, per unit area, per 1°C rise of temperature is called, the coefficient of areal expansion, αA = \(\frac{\Delta \mathrm{a}}{\mathrm{a} \times \Delta \mathrm{t}} /{ }^{\circ} \mathrm{C}\)
→ The increase in volume, per unit volume, per 1°C rise of temperature is called, the coefficient of volume expansion, αv = \(\frac{\Delta v}{v \times \Delta t} /{ }^{\circ} \mathrm{C}\)
→ αl = αA = αv = 1 : 2 : 3 (or) \(\frac{\alpha_l}{1}: \frac{\alpha_{\mathrm{A}}}{2}: \frac{\alpha_{\mathrm{v}}}{3}\)
→ The change in temperature of a substance, when a given quantity of heat is absorbed, Then it is called Heat capacities S = \(\frac{\Delta Q}{\Delta T}\).
→ The amount of heat absorbed (Or) rejected to change the temperature of unit mass in called specific heat capacity of the substance s = \(\frac{s}{m}=\frac{1}{m} \frac{\Delta Q}{\Delta T}\).
→ Molar specific heat is defined as the amount of heat absorbed (or) rejected to change the temperature of one mole of a substance C = \(\frac{s}{\mu}=\frac{1}{\mu} \frac{\Delta Q}{\Delta T}\).
→ The phenomenon of refreezing is called regelation.
→ The quantity of heat absorbed (or) liberated during the change of state by unit mass of substance, with out any change in temperature is called latent heat.
→ The latent heat of fusion (Lf) is the heat per unit mass required to change a substance from solid into liquid at the same temperature and pressure.
→ The latent heat of vaporisation (Lv) is the heat per unit mass required to change a substance from the liquid to the vapour state without change in the temperature and pressure.
→ Transfer of heat takes place in three modes from high temperature regions to low temperature regions in matter. These modes are conduction, convection and radiation.
→ Conduction of heat is possible in matter by transfer of energy among the molecules through collisions. The bulk of the material does not move while the molecules vibrate about their mean position and collide with each other.
→ The ability of conducting heat varies from material to material. It is measured by a quantity known as coefficient thermal conductivity.
→ Convection is the energy transfer by means of bulk movement of the fluid-
→ Convection is of two types
- natural convection
- forced convection.
→ Natural convection occurs when fluid with different density values moves under gravity.
→ Forced convection takes place when a fluid is allowed to pass over a body with different temperature forcibly.
→ Thermal radiation does not require a material medium.
→ Every body emits thermal radiation at all temperatures above absolute zero and exchanges heat energy with surroundings. This is known as Prevost theory.
→ The energy flux emitted by unit surface area of a radiating body is known as emissive power. Its units is Jm2s-1 or Wm-2. Dimensional formula is [MT-3].
→ The ratio of energy flux absorbed in certain time to total energy flux incident on the body in the same time is known as absorptive power α . α can not be greater than 1.
For a black body absorptive power at all wave lengths is 1.
→ The ratio of emissivity of a body to its absorptivity is same for all bodies at a given temperature and equals to the emissivity of a black body at the same temperature. This is KirchhofFs law of radiation.
→ Emissive power of a black body is proportional to the forth power of the absolute temperature. P = σAT-4. P emissive power, σ Stefan’s constant and equal to 5.67 × 10-8 W/m4 k4 this can be written for a body (which is not a black body) as follows :
P = eλ σ AT4 where eλ is the emissivity of the body.
→ Newton’s law of cooling : The rate of loss of heat is directly proportional to the difference in temperature between the body and its surroundings provided the temperature difference is small.
\(\frac{-\mathrm{dQ}}{\mathrm{dt}}\) = α (TB – TS)