Heat Transfer Mechanisms

When you rub your palms together, the friction between the skin surfaces converts kinetic energy from the rubbing motion into thermal energy (heat). This is why friction always produces warmth - it's energy transformation from mechanical to thermal.

Radiation is the only heat transfer method that does not require a material medium. It occurs through electromagnetic waves (infrared radiation). Conduction requires direct contact, convection requires bulk motion of fluids, but radiation can travel through vacuum.

The earth's surface absorbs solar insolation, becomes heated, and then radiates longwave terrestrial radiation that warms the atmosphere from below. Conduction affects only the lowest air layer, while convection redistributes this heat vertically but isn't the primary heating source.

Above a fire, all three heat transfer mechanisms operate: conduction through the combustion zone, convection of hot gases rising upward, and thermal radiation emitted in all directions. The upward convection concentrates heat directly above, while radiation spreads outward, making it hottest directly above.

Yes, it is correct. A wire becomes hot when it is heated for a long time and hence shows heating effect.

The greenhouse effect refers to circumstances where the short wavelengths of visible light from the sun pass through a transparent medium and are absorbed, but the longer wavelengths of the infrared re-radiation from the heated objects are unable to pass through that medium. The trapping of the long wavelength radiation leads to more heating and a higher resultant temperature.

An isenthalpic process is a process that proceeds without any change in enthalpy, H. In a steady-state, steady-flow process, significant changes in pressure and temperature can occur to the fluid and yet the process will be isenthalpic if there is no transfer of heat to or from the surroundings, no work done on or by the surroundings, and no change in the kinetic energy of the fluid.

A heat pump uses some amount of external high-grade energy to accomplish the desired transfer of thermal energy from heat source to heat sink. So temperature is a measure of the thermal energy per particle of matter or radiation.

Poikilotherms have variable body temperature (c), Homotherms maintain constant temperature (a), Ectotherms gain heat from outside (d), and Endotherms generate internal heat (b). Option B correctly matches all pairs.

The particles of matter possess kinetic energy and thus, are constantly moving. Kinetic energy of particles is directly proportional to the temperature. The temperature of hot food is more, so the particles of hot vapours coming out of hot sizzling food have higher kinetic energy, i.e. they move faster and hence, the smell of hot sizzling food reaches several metres away. Moreover, the particles in vapour state do not have forces of attraction and they can easily move.

According to the Stefan-Boltzmann law and Kirchhoff's radiation law, a black surface is a nearly perfect emitter and absorber of thermal radiation (good black body). A rough surface has greater effective surface area for emission compared to a polished one. Therefore, a black and rough surface radiates heat most rapidly. Polished surfaces are poor emitters, while white surfaces reflect more radiation than they emit. This is why radiator fins are often black and rough.

Correct Answer: ignition temperature

The lowest temperature at which a substance catches fire is called its ignition temperature.

A matchstick does not catch fire until its temperature is raised to its ignition temperature and the ignition temperature of this type of substance is higher than room temperature.