Thermal Properties of Matter MCQs for NEET — Physics Questions with Answers

Point 8 in the summary states: 'The latent heat of vaporisation (Lv) is the heat per unit mass required to change a substance from liquid to the vapour state without change in the temperature and pressure.'

The text states: 'For a body, which is a perfect radiator, the energy emitted per unit time (H) is given by $H = A\sigma T^4$'. This shows the proportionality to the fourth power of the absolute temperature.

The introduction mentions: 'Along the way, you will find out why blacksmiths heat their iron ring before fitting on the rim of a wooden wheel of a horse cart'. This action is done to expand the iron ring due to heating (thermal expansion), allowing it to fit over the wooden rim. Upon cooling, it contracts and forms a tight fit.

The introduction states: 'You will also learn what happens when water boils or freezes, and its temperature does not change during these processes even though a great deal of heat is flowing into or out of it.' This describes the concept of latent heat, where the supplied heat energy causes a phase change rather than a temperature change.

Point 6 in the summary provides the relation: '$\alpha_v = 3 \alpha_l$'.

Point 11 in the summary states: 'Newton’s Law of Cooling says that the rate of cooling of a body is proportional to the excess temperature of the body over the surroundings'. This 'excess temperature' is the difference between the body's temperature and the surrounding's temperature.

The text states: 'One, therefore, defines a dimensionless fraction e called emissivity and writes, H = $Ae\sigma T^4$'. It also clarifies that 'e = 1 for a perfect radiator'.

The paragraph about Wien's law states: 'Light from the moon is found to have a maximum intensity near the wavelength $14 \mu m$. By Wien’s law, the surface of the moon is estimated to have a temperature of 200 K.'

The text explains: 'Internal energy is thus, the sum of molecular kinetic and potential energies in the frame of reference relative to which the centre of mass of the system is at rest. Thus, it includes only the (disordered) energy associated with the random motion of molecules of the system.' It further adds: 'The important thing about internal energy is that it depends only on the state of the system, not on how that state was achieved. Internal energy U of a system is an example of a thermodynamic ‘state variable’'.

The NCERT text states, 'Convection is a mode of heat transfer by actual motion of matter.' This distinguishes it from conduction (molecular vibration) and radiation (electromagnetic waves).