This set of Food Processing Unit Operations Multiple Choice Questions & Answers (MCQs) focuses on “Heat Conduction”.
1. Ice has __________ thermal conductivity than water.
a) lower
b) higher
c) same
d) very lower
View Answer
Explanation: Ice has higher thermal conductivity than water. This is due to the molecular arrangement in solids and liquids where solid has packed structure of molecules and stronger bonding between molecules compared to liquids. Therefore the thermal conductivity of frozen foods is higher than the foods at normal temperature.
2. Which material has highest thermal conductivity?
a) Diamond
b) Copper
c) Silver
d) Bronze
View Answer
Explanation: Diamond has highest thermal conductivity around room temperature along with the graphite and graphene. The thermal conductivity of diamond is 2000 watts per meter per Kelvin, which is five times higher than copper.
3. Which of the following is the best insulator?
a) Silica aerogels
b) Manganese aerogels
c) Potassium aerogels
d) Lead aerogels
View Answer
Explanation: The best insulator is silica aerogels. The thermal conductivities of silica aerogel is less than 0.03 W/m*K in atmosphere.The liquid is removed from the gel without collapsing its structure, thus creating air pockets in the medium. This slows down the heat transfer and act as the insulator.
4. Are these statements about the thermal conductivity true?
Statement 1: Thermal conductivity is an extrinsic property.
Statement 2: It involves in the bulk motion of the molecules during heat transfer.
a) True, False
b) True, True
c) False, True
d) False, False
View Answer
Explanation: Thermal conductivity is the intrinsic property of the material. It refers to its ability to conduct heat. Heat transfer by conduction involves transfer of energy within a material without any motion of the molecules during heat transfer.
5. Which of the following example does not explain conduction?
a) The heat from a hot liquid makes the cup itself hot
b) Walking on the beach on a hot summer day will warm the feet
c) A metal spoon becomes hot from the boiling water inside the pot
d) The formation of sea and land breeze
View Answer
Explanation: The formation of sea and land breeze is an example of convection. The other examples are due to conduction where transfer of heat in internal energy by minute collision of particles and electron movement within a body.
6. Which law governs the thermal conductivity?
a) Fourier’s law
b) Pascal law
c) Newton law
d) Planks law
View Answer
Explanation: The Fourier’s law governs the thermal conductivity. This law states that the time rate of heat transfer through a material is directly proportional to the negative gradient in the temperature and to area, at its right angle to that gradient through which the heat flows.
7. What are factors of heat capacity?
a) Heat energy, time
b) Heat energy, temperature
c) Heat energy, temperature, time
d) Temperature, time
View Answer
Explanation: Heat energy and temperature plays an important factor in calculating heat capacity. The heat capacity is defined as the ratio of amount of heat energy supplied and change in temperature.
8. Is thermal diffusivity and thermal conductivity related?
a) True
b) False
View Answer
Explanation: The thermal diffusivity is the thermal conductivity divided by density of the material and specific heat capacity at a constant pressure. It measures the ability to conduct thermal energy relative to its ability to the heat energy. High diffusivity means rapid heat transfer.
9. According to_________ law, the conductive heat flux is linearly proportional to the temperature gradient.
a) Fourier’s law
b) Pascal law
c) Newton law
d) Stefan-Boltzmann Law
View Answer
Explanation: According to Fourier’s law, the conductive heat flux is linearly proportional to the temperature gradient.Pascal law deals with the fluid mechanics of the substance. Newton law deals with the heat convection. Stefan-Boltzmann Law deals with the thermal radiation.
10. Which is the slowest mode of heat transfer?
a) Conduction
b) Convection
c) Radiation
d) Both radiation and convection
View Answer
Explanation: Conduction is the slowest mode of heat transfer because it takes place from particle to particle. The fastest mode of heat transfer is radiation as it travels at the speed of light.
Sanfoundry Global Education & Learning Series – Food Processing Unit Operations.
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