Thermal | MCQs

Explanation

According to Kirchhoff's law:

Coefficient of emission (e) + Coefficient of reflection (r) + Coefficient of transmission (t) = 1

Given: t = 0.33, r = 0.64

e + 0.64 + 0.33 = 1

e = 1 - 0.97

= 0.03

Explanation

Note According to KMU MDCAT answer key the correct answer is 'C'

A black body is an ideal radiator that radiates energy unequally at all wavelengths.

The intensity of radiation emitted by a black body varies with wavelength, following Planck's law.

The spectral distribution of this radiation is characterized by a peak wavelength that shifts depending on the temperature of the black body, which is described by Wien's displacement law.

Explanation

The average translational kinetic energy of molecules is directly proportional to the temperature (in Kelvin).

Since the temperature is increased from 300 K to 750 K, the average translational kinetic energy will also increase by a factor of 750/300 = 2.5.

So, the average translational energy at 750 K will be:

6 x 10^-20 J x 2.5 = 1.5 x 10^-19 J

Explanation

Due to heating, when a free electron is produced than simultaneously a hole is also produced.

Explanation

The increase in length (or volume) of solids when heated is specifically called thermal expansion.

Key Information:

Thermal Expansion:

• Occurs due to increased atomic vibrations with temperature.
• Linear expansion: Change in length (e.g., railroad tracks expanding in summer).
• Volumetric expansion: Change in 3D dimensions (e.g., mercury in thermometers).

Explanation

The decomposition reaction is: 

ZnCO 3(s)→ZnO(s)+CO 2(g) One mole of ZnCO₃ produces one mole of CO₂, so 10 moles will produce 10 moles of CO₂.

The molar mass of CO₂ is: 

CO₂=12+(16×2)=44g/mol Therefore, 

10 moles of CO₂=10×44=440g.

Explanation

The percentage of a sample of HBr decomposes at 430 °C. is 0.1.

Explanation

• Epoxy paints are commonly used to coat industrial equipment, including thermal power station components, due to their excellent adhesion, corrosion resistance, and durability. 
• Epoxy paints form a strong, chemical-resistant film that protects the underlying metal from corrosion and wear.

Explanation

Boric acid on heating at 100oC gives HBO2.

On heating orthoboric acid (H3BO3) at 370 K or above,

It changes to metaboric acid (HBO2).

On further heating, this yields boric oxide B2O3.

Additional information:

Orthoboric acid, $H_{3}B{O}_3$ is a white crystalline solid, with soapy touch.

It is sparingly soluble in water but highly soluble in hot water.

Explanation

The process by which a substance changes from the solid phase to the liquid phase is known as melting.