1. Thermal energy is transported through the molecules due to _______and _______
a) lattice waves, free electrons
b) lattice waves, free protons
c) free protons, free electrons
d) lattice waves, longitudinal waves
Discussion
Explanation: Thermal energy is transported through the molecules due to lattice waves and free electrons. In pure metals, the conduction of heat is based on the flow of free electrons and the effect of lattice waves is considered as negligible. In alloys and nonmetallic solids, since they are only few free electrons, conduction of heat is due to lattice vibrations in between the molecules.
2. ________ is the heat content in a system per unit mass.
a) Specific heat
b) Enthalpy
c) Entropy
d) Latent heat
Discussion
Explanation: Enthalpy is the heat content in a system per unit mass. Its unit is J/kg in the SI system. It is a thermodynamic property that is governed by the state of the system and it is expressed as H=U+PV, where H is the enthalpy, U is internal energy, and P is pressure and V is volume.
3. The effect of ______on the system is seen only as a phase change like the melting of ice.
a) Specific heat
b) Enthalpy
c) Entropy
d) Latent heat
Discussion
Explanation: Latent heat is the also known as hidden energy. It can be defined as the heat that is released or absorbed by a system during constant temperature process is called latent heat. The effect is seen only as a phase change like boiling of water or the melting of ice.
4. Are these statements about the specific heat true?
Statement 1: Specific heat of ice is double the specific heat of water.
Statement 2: Specific heat of foods decreases during freezing.
a) True, False
b) True, True
c) False, True
d) False, False
Discussion
Explanation: Specific heat of ice is 2.1 kJ/kg K and specific heat of water. 4.218 kJ/kg K. Therefore the specific heat of ice is half of the specific heat of water. Specific heat of foods decreases during freezing as there is a continuous phase change from water to ice.
5. Which of the following is not a thermal property in foods?
a) Surface heat transfer coefficient
b) Thermal diffusivity
c) Specific volume
d) Entropy
Discussion
Explanation: The surface heat transfer coefficient is not a thermal property. It is required to design heat transfer equipment for processing foods where convection is involved. It depends on the fluid velocity, product size and shape, surface roughness, arrangement and packaging.
6. ______ is the ability of a material to transmit a thermal disturbance.
a) Specific heat
b) Thermal diffusivity
c) Entropy
d) Latent heat
Discussion
Explanation: Thermal diffusivity is the ability of a material to transmit a thermal disturbance. It determines heat propagation and diffusion through a material. It helps in estimating the process time of canning, cooking and cooling. Water content, composition, temperature and porosity affect thermal diffusivity.
7. Who discovered latent heat?
a) Joseph Black
b) Josiah Willard Gibbs
c) Henri Becquerel
d) Stephen Gray
Discussion
Explanation: Joseph Black discovered latent heat. Josiah Willard Gibbs discovered enthalpy. Henri Becquerel discovered radiation. Stephen Gray discovered electrical conduction.
8. Which liquid has highest latent heat of vaporization?
a) Water
b) Alcohol
c) Oil
d) Mecury
Discussion
Explanation: Water has highest latent heat of vaporization. It is determined bythe extent of the latent heat on the molecules and molecular bonding in liquid and solid states.
9. Which describes the level of microbial destruction obtained by thermal treatment?
a) F0 value
b) Thermal death time
c) D value
d) Z value
Discussion
Explanation: The level of microbial destruct that is obtained by thermal treatment is known as sterilizing value (F0) of the given food product. The results are calculated at 121.1°C temperature. The unit is minutes.
10. ________ relates the resistance of an organism to differing temperatures.
a) F0 value
b) Thermal death time
c) D value
d) Z value
Discussion
Explanation: Z- value is defined as the temperature (in degree) at which a tenfold reduction in D-value is attained. The main application of Z- value is in the calculating the thermal death time of a microorganism.