This set of Food Processing Unit Operations Multiple Choice Questions & Answers (MCQs) focuses on “Heat Radiation”.
1. Which is the fastest mode of heat transfer?
a) Conduction
b) Convection
c) Radiation
d) Both conduction and convection
View Answer
Explanation: The fastest mode of heat transfer is radiation as it travels at the speed of light. Conduction is the slowest mode of heat transfer because it takes place from particle to particle.
2. Which law governs the thermal radiation?
a) Fourier’s law
b) Pascal law
c) Newton law
d) Stefan-Boltzmann Law
View Answer
Explanation: Stefan-Boltzmann Lawgoverns the thermal radiation. It statesthat the total radiant heat power emitted from a surface is proportional to the fourth power of its absolute temperature.
3. Are these statements about the thermal radiation true?
Statement 1: It follows Stefan-Boltzmann Law.
Statement 2: It also depends on Wien’s Displacement Law.
a) True, False
b) True, True
c) False, True
d) False, False
View Answer
Explanation: Thermal radiation follows Planks law and also Wien’s Displacement Law. Stefan-Boltzmann Law states that the total radiant heat power emitted from a surface is proportional to the fourth power of its absolute temperature.Wien’s Displacement Law states that a hotter object will emit radiation with a shorter wavelength.
4. The emissivity of radiation is between__________
a) 0 and 1
b) 0 and 10
c) 0 and 15
d) 0 and 11
View Answer
Explanation: The emissivity of radiation is between0 and 1. It can be defined as the ratio of the thermal radiation from the surface to the radiation from an ideal black surface at a constant temperature. This is derived under Stefan–Boltzmann law.
5. In thermal radiation, thermal energy is converted to ___________________
a) kinetic energy
b) potential energy
c) electromagnetic energy
d) thermal energy
View Answer
Explanation: In thermal radiation, thermal energy is converted to electromagnetic energy. This is achieved by the thermal motion of the particles in the substance. All the substance with a temperature greater than absolute zero emits the thermal radiation. The motion of the particle results in acceleration of charge and dipole oscillation which produces electromagnetic energy.
6. What is the wavelength of thermal radiation?
a) 0.1 μm to 1000 μm.
b) 1 μm to 100 μm.
c) 0.01 μm to 100 μm.
d) 0.1 μm to 100 μm.
View Answer
Explanation: The thermal radiation is the electromagnetic radiation emitted from all the substance that is at non-zero temperature in the wavelength ranging from 0.1 μm to 100 μm. This includes part of ultraviolet rays, all of the visible and infrared rays.
7. Can a good insulator prevent radiation?
a) True
b) False
View Answer
Explanation: Hot objects radiate infra-red electromagnetic waves, so therefore insulation against heat transfer by radiation is done by using reflective materials. The thermos bottle has a shiny material along with a lining to prevent heat conduction. This shiny material reflects heat from the radiation from inside as well as outside the bottle.
8. What are factors of thermal radiation?
a) Time
b) Temperature
c) Volume
d) Pressure
View Answer
Explanation: Temperature plays an important factor in thermal radiation. The heat capacity is defined as the ratio of amount of heat energy supplied and change in temperature. According to Stefan-Boltzmann Law, the total radiant heat power emitted from a surface is proportional to the fourth power of its absolute temperature.
9. According to ___________, the wavelength of the emitted radiation is inversely proportional to its frequency.
a) Fourier’s law
b) Pascal law
c) Newton law
d) Plank’s law
View Answer
Explanation: According to Plank’s law, the wavelength of the emitted radiation is inversely proportional to its frequency. It is defined as the spectral density of the electromagnetic energy emitted by a black body in thermal equilibrium at a given temperature normally when the net flow of energy and matter is zero between the body and its environment.
10. ____________ gives the relationship between wavelength and temperature.
a) Fourier’s law
b) Wein’s law
c) Newton law
d) Plank’s law
View Answer
Explanation: Wein’s law gives the relationship between wavelength and temperature. Wien’s displacement law is defined as the spectral radiance of black body radiation per unit wavelength. The maximum wavelength can be calculated by dividing Wien’s displacement constant with Temperature.
Sanfoundry Global Education & Learning Series – Food Processing Unit Operations.
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