Question 1

Tea pots are highly polished

Accepted Answer

B

Question 2

A shpere, a cube and a disc all of the same material, quality and volume are heated to 900K and left in air. Which of these will have the lowest rate of cooling

Accepted Answer

The sphere will have the lowest rate of cooling because it has the smallest surface area to volume ratio compared to the cube and the disc, leading to less heat loss through radiation.

Question 3

The overall co-efficient of heat transfer is expressed as

Accepted Answer

The overall coefficient of heat transfer is expressed in terms of energy per unit area, per unit time, per degree temperature difference, which is kcal/m^2/hr/°C.

Question 4

A fur coat on an animal will help the animal to be

Accepted Answer

A fur coat provides insulation, helping animals retain body heat and stay warm in cold winter conditions.

Question 5

The wagelength of X-rays is

Accepted Answer

The answer of The wagelength of X-rays is
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Question 6

There are two spheres of copper the ratio of their radii being 1 : 3 both at the same temperature. The ration of heat contents will be

Accepted Answer

The heat content of an object is directly proportional to its volume. Since the spheres are made of the same material (copper) and are at the same temperature, the ratio of their heat contents will be equal to the ratio of their volumes. The volume of a sphere is given by $V = \frac{4}{3}\pi r^3$, where $r$ is the radius. If the ratio of their radii is 1:3, then the ratio of their volumes (and thus their heat contents) will be $1^3 : 3^3 = 1:27$.

Question 7

Which dimensionless number can be used for convective heat transfer?

Accepted Answer

The Nusselt number is a dimensionless number used in convective heat transfer to characterize the convective heat transfer coefficient.

Question 8

Essential requirement for the transfer of heat from one body to another is

Accepted Answer

Heat transfer occurs when there is a temperature difference between two bodies, regardless of their state (solid, liquid, or gas), whether they are in contact, or if one has an internal heat source.

Question 9

The ratio of specific heats of a gas is 1.4 and the value of specific heat at constant pressure is 7.0 cal/mole °C. The difference between specific heat at constant presure and specific heat at constant volume will be

Accepted Answer

The difference between specific heat at constant pressure (Cp) and specific heat at constant volume (Cv) is given by Cp - Cv = R, where R is the gas constant. Given the ratio of specific heats (γ = Cp/Cv) is 1.4, and Cp is 7.0 cal/mole°C, we can find Cv using γ = Cp/Cv = 1.4, which gives Cv = Cp/1.4 = 5 cal/mole°C. Therefore, Cp - Cv = 7 - 5 = 2 cal/mole°C.

Question 10

The reflectance of a black body is

Accepted Answer

A black body is an idealized physical body that absorbs all incident electromagnetic radiation, regardless of frequency or angle of incidence. Therefore, it does not reflect any light, making its reflectance zero.

Question 11

A dimensionless heat transfer coefficient which gives a measure of the ratio of the heat transfer rate to the rate at which heat would be conducted within the fluid under a temperature gradient is known as

Accepted Answer

The Nusselt number is a dimensionless heat transfer coefficient that measures the ratio of convective to conductive heat transfer across a boundary.

Question 12

If thermal conductivity of a material of wall varies as ko (1 -t ). The temperature at the centre of the wall will be

Accepted Answer

The temperature at the centre of the wall will be less than that in case of constant thermal conductivity because the thermal conductivity of the material decreases with increasing temperature.

Question 13

Dynamic similarity is the similarity of

Accepted Answer

Dynamic similarity involves the similarity of forces, including inertial, viscous, gravitational, and surface tension forces, among others, in model testing and analysis.

Question 14

Which of the following is an example of absorption?

Accepted Answer

Absorption is the process of taking in or absorbing something. In the given options, the removal of moisture from gasoline is an example of absorption.

Question 15

The sensible heat of hot industrial gases can be recovered by a

Accepted Answer

Both regenerators and recuperators are types of heat exchangers used to recover sensible heat from hot industrial gases. A regenerator temporarily stores heat in a thermal storage medium and then transfers it, while a recuperator directly transfers heat from one fluid to another.

Question 16

For glass wool the thermal conductivity varies from sample to sample because of variations in

Accepted Answer

The thermal conductivity of glass wool can vary due to differences in its structure, composition, density, and porosity. Each of these factors can influence how well the material insulates by affecting the movement of heat through the material.

Question 17

Metals are good conductors of heat because

Accepted Answer

Metals are good conductors of heat primarily because they contain free electrons. These free electrons move easily between atoms, transferring thermal energy efficiently throughout the material.

Question 18

Which one of the following cannot be unit of thermal conductivity?

Accepted Answer

Thermal conductivity is measured in units of energy per time per distance per temperature. "Watt / m² K" is a unit of heat flux, not thermal conductivity.

Question 19

A body cools from 80°C to 70°C in 10 minutes. The time taken by the body for further cooling to 60°C will be

Accepted Answer

According to Newton's Law of Cooling, the rate of cooling is proportional to the temperature difference between the body and its surroundings. As the body cools, this temperature difference decreases, leading to a slower rate of cooling. Therefore, it will take more than 10 minutes to cool from 70°C to 60°C.

Question 20

Calorific value of Indian coal is

Accepted Answer

The calorific value of Indian coal typically ranges around 3300 kcal/kg, although it can vary depending on the specific type and grade of coal.

Quiz 15: Heat Transfer and Thermodynamics