Heat And Mass Transfer - Study Mode

[#41] Unit of thermal conductivity in S.I. units is
Correct Answer

(D) Option (B) and (C) above

Explanation

Solution: Thermal conductivity is measured in watts per meter-kelvin W/m °K and J/m °K sec.

[#42] According to Wien's law, the wavelength corresponding to maximum energy is proportion to
Correct Answer

(A) Absolute temperature (T)

Explanation

Solution: Wien's law formula The equation describing Wien's law is very simple: $${lambda _{max }} = frac{{ ext{b}}}{{ ext{T}}}$$ where, • $${lambda _{max }}$$ xa0is the aforementioned peak wavelength of light • T is an absolute temperature of a black body • b = 2.8977729 mm$$ cdot $$K is the Wien's displacement constant Although the relation between wavelength and frequency of electromagnetic waves is fairly simple ($$lambda $$ × f = c), we can't work out the peak frequency f max by this analogy. The reason is that spectral radiance is a sort of energy density function, so its shape and maximum depend on the argument (wavelength or frequency in our case). Knowing that the formula for the peak frequency is: f max = k × T, where k = 5.8789232 × 10 10 Hz/K is a numerical constant. Wien's law formula can't be derived from classical physics. Numerous observations that confirm this law are among experiments (e.g., photoelectric effect), which contribute to the creation of quantum mechanics.

[#43] Which of the following has least value of conductivity?
Correct Answer

(D) Air

Explanation

Solution: air has the least value of conductivity

[#44] According to Prevost theory of heat exchange
Correct Answer

(C) All bodies above absolute zero emit radiation

Explanation

Solution: According to Prevost theory of heat exchange: Every material body, at any temperature above absolute zero, radiates heat to the surroundings and at the same time absorbs heat from the surroundings. The rate of emission of heat by a body depends upon its absolute temperature.

[#45] Conduction is a process of heat transfer
Correct Answer

(A) From one particle of the body to another without the actual motion of the particles

Explanation

Solution: Conduction is the process by which heat energy is transmitted through collisions between neighboring atoms or molecules.
Conduction occurs more readily in solids and liquids, where the particles are closer to together, than in gases, where particles are further apart.