Physics · Science General

Heat Transfer Mechanisms

828 Questions

Heat Transfer Mechanisms deal with the movement of thermal energy through conduction, convection, and radiation. It involves practical applications like ocean heat storage and atmospheric heating. These fundamental physics concepts are frequently asked in general science sections.

Thermal conductionHeat convectionThermal radiationSpecific heatStates of matter

Heat Transfer Mechanisms Questions

Multiple choice stefan's law black body radiation heat transfer thermal properties physics

The amount of heat energy radiated per second by a surface depends upon:

  1. Area of the surface

  2. Difference of temperature between the surface and its surroundings

  3. Nature of the surface

  4. All the above
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Refer Stefan's Law of Radiation: $Q = \eta \sigma A \delta{T}^{4}$
where, $\sigma = conductivity\ A$  = area $T$ = difference of the temperature 

Multiple choice stefan's law black body radiation heat transfer thermal properties physics

All bodies emit heat energy from their surfaces by virtue of their temperature. This heat energy is called radiant energy of thermal radiation. The heat that we receive from the sun is transferred to us by a process which, unlike conduction orconvection, does not require the help of a medium in the intervening space which is almost free of particles. Radiant energy travels in space as electromagnetic spectrum. Thermal radiations travel through vacuum with the speed oflight. Thermal radiations obey the same laws of reflection and refraction as light does. They exhibit the phenomena of interference, diffraction and polarization as light does.
The emission of radiation from a hot body is expressed in terms of that emitted from a reference body (called the black body) at the same temperature. A black body absorbs and hence emits radiations of all wavelengts. The total energy E emitted by a unit area of a black bodyper second is given by $E =\sigma T^{4}$ where T is the absolute temperature of the body and $\sigma $ is a constant known as Stefans constant. If the body is not a perfect black body, then $E =\varepsilon \sigma  T^{4}$where $\varepsilon $ is the emissivity of the body.

Which of the following devices is used to detect thermal radiations?

  1. Constant volume air thermometer

  2. Platinum resistance thermometer

  3. Thermostat

  4. Thermopile
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Thermopile is a very sensitive device which converts thermal energy to electrical energy.
It is used to detect thermal radiations.

Multiple choice stefan's law black body radiation heat transfer thermal properties physics

All bodies emit heat energy from their surfaces by virtue of their temperature. This heat energy is called radiant energy of thermal radiation. The heat that we receive from the sun is transferred to us by a process which, unlike conduction or convection, does not require the help of a medium in the intervening space which is almost free of particles. Radiant energy travels in space as electromagnetic spectrum. Thermal radiations travel through vacuum with the speed of light. Thermal radiations obey the same laws of reflection and refraction as light does. They exhibit the phenomena of interference, diffraction and polarization as light does.
The emission of radiation from a hot body is expressed in terms of that emitted from a reference body (called the black body) at the same temperature. A black body absorbs and hence emits radiations of all wavelengths. The total energy E emitted by a unit area of a black body per second is given by $E =\sigma T^{4}$ where T is the absolute temperature of the body and $\sigma $ is a constant known as Stefans constant. If the body is not a perfect black body, then $E =\varepsilon \sigma  T^{4}$where $\varepsilon $ is the emissivity of the body.

From stefan-Boltzmann law, the dimensions of Stefans constant $\sigma $ are :

  1. $ML^{-2}T^{-2}K^{-4}$
  2. $ML^{-1}T^{-2}K^{-4}$
  3. $MLT^{-3}K^{-4}$
  4. $ML^{0}T^{-3}K^{-4}$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Stefan's law:
$E = \sigma T^{4}$ 
$\sigma = E/ T^{4}$
$E = energy/(area*time) = ( M L^{2} T^{-2} )/ ( L^{2} T)$
$\sigma =  M T^{-3} K^{-4}$

Multiple choice stefan's law black body radiation heat transfer thermal properties physics

All bodies emit heat energy from their surfaces by virtue of their temperature. This heat energy is called radiant energy of thermal radiation. The heat that we receive from the sun is transferred to us by a process which, unlike conduction or convection, does not require the help of a medium in the intervening space which is almost free of particles. Radiant energy travels in space as electromagnetic spectrum. Thermal radiations travel through vacuum with the speed of light. Thermal radiations obey the same laws of reflection and refraction as light does. They exhibit the phenomena of interference, diffraction and polarisation as light does.
The emission of radiation from a hot body is expressed in terms of that emitted from a reference body (called the black body) at the same temperature. A black body absorbs and hence emits radiations of all wavelengths. The total energy $E$ emitted by a unit area of a black body per second is given by $E =\sigma T^{4}$ where $T$ is the absolute temperature of the body and $\sigma $ is a constant known as Stefan's constant. If the body is not a perfect black body, then $E =\varepsilon \sigma  T^{4}$where $\varepsilon $ is the emissivity of the body.

In which region of the electromagnetic spectrum do thermal radiations lie?

  1. Visible region

  2. Infrared region

  3. Ultraviolet region

  4. Microwave region
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Stefan's law states:
$E = \sigma T^{4}$ 
Normally temperature of a body never exceeds more than 1000K. 
As the temperature is quite less compared to the sun's temperature. Photons of this radiation have less energy and hence greater wavelength and fall into infrared region.
Alternately by Wein's displacement law
$ \lambda _{max} T = constant$
By applying above law on sun and normal body, wavelength of normal thermal radiation falls in infrared region.

Multiple choice stefan's law black body radiation heat transfer thermal properties physics

All bodies emit heat energy from their surfaces by virtue of their temperature. This heat energy is called radiant energy of thermal radiation. The heat that we receive from the sun is transferred to us by a process which, unlike conduction or convection, does not require the help of a medium in the intervening space which is almost free of particles. Radiant energy travels in space as electromagnetic spectrum. Thermal radiations travel through vacuum with the speed of light. Thermal radiations obey the same laws of reflection and refraction as light does. They exhibit the phenomena of interference, diffraction and polarization as light does.
The emission of radiation from a hot body is expressed in terms of that emitted from a reference body (called the black body) at the same temperature. A black body absorbs and hence emits radiations of all wavelengths. The total energy E emitted by a unit area of a black body per second is given by $E =\sigma T^{4}$ where T is the absolute temperature of the body and $\sigma $ is a constant known as Stefan's constant. If the body is not a perfect black body, then $E =\varepsilon \sigma  T^{4}$where $\varepsilon $ is the emissivity of the body.

What is the SI unit of Stefan's constant?

  1. $Js^{-1}K^{-4}$
  2. $Wm^{-1}K^{-4}$
  3. $Wm^{-2}K^{-4}$
  4. $Jm^{-2}K^{-4}$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Stefan's law:
$E = \sigma T^{4}$ 
$\sigma = E/ T^{4}$
$E = energy/(area*time) = W m^{-2}$
$\sigma =  W m^{-2} K^{-4}$

Multiple choice evs sources of water the lithosphere and the hydrosphere first aid safety and first aid

Transfer of heat within water is by

  1. Conduction

  2. Convection

  3. Radiation

  4. None of the above
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The water is a poor conductors of heat so do not heated by conduction.  When water is heated, the water became lighter. Hot water rises up. The cold water from the sides moves  down towards the source of heat. This water also gets hot and rises and water from the sides moves down.  This process continues till the whole water gets heated. This mode of heat transfer is known as convection.

So, the correct answer is 'Convection'.

Multiple choice

What is the primary mechanism by which permeable pavements reduce the heat island effect?

  1. Evaporation of infiltrated water

  2. Reflection of solar radiation

  3. Convection of heat from the pavement surface

  4. All of the above
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Permeable pavements reduce the heat island effect primarily through the evaporation of infiltrated water, which cools the pavement surface and surrounding air.

Multiple choice

The dimensionless number that characterizes the ratio of heat transfer by convection to heat transfer by conduction is:

  1. Reynolds Number

  2. Mach Number

  3. Prandtl Number

  4. Nusselt Number
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Nusselt Number is used to characterize the heat transfer between a surface and a fluid.

Multiple choice

Which partial differential equation governs the diffusion of heat?

  1. Poisson's Equation

  2. Laplace's Equation

  3. Heat Equation

  4. Wave Equation
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The Heat Equation is a partial differential equation that describes the diffusion of heat in a medium. It is a second-order linear partial differential equation.

Multiple choice

Which partial differential equation governs the steady-state temperature distribution in a two-dimensional region?

  1. Poisson's Equation

  2. Laplace's Equation

  3. Heat Equation

  4. Wave Equation
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Laplace's Equation is a partial differential equation that governs the steady-state temperature distribution in a two-dimensional region. It is a second-order linear partial differential equation.

Multiple choice

The thermal conductivity of a material is a measure of its ability to:

  1. Conduct heat

  2. Store heat

  3. Generate heat
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Thermal conductivity is a measure of a material's ability to transfer heat through conduction. It is defined as the amount of heat transferred through a unit area of the material per unit time per unit temperature gradient.

Multiple choice

The specific heat capacity of a substance is the amount of heat required to:

  1. Raise the temperature of one gram of the substance by one degree Celsius

  2. Raise the temperature of one kilogram of the substance by one degree Celsius

  3. Raise the temperature of one mole of the substance by one degree Celsius
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Specific heat capacity is a measure of the amount of heat required to raise the temperature of a unit mass of a substance by one degree Celsius. It is a characteristic property of the substance and is used to calculate the amount of heat required to change the temperature of a given mass of the substance.

Multiple choice

What is the role of buoyancy in convection?

  1. It causes warm air to rise and cool air to sink.

  2. It causes cool air to rise and warm air to sink.

  3. It causes air to move horizontally.

  4. It causes air to move vertically.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Buoyancy causes warm air to rise and cool air to sink.