Tag: thermal energy transfers

Questions Related to thermal energy transfers

Which of the following process(es) occur(s) during the convective transfer of heat within a large volume of air? 

physics transfer of heat applications of convection convection thermal energy transfers

  1. A continuous flow of warmer and cooler parts of air is established.

  2. The flow of air molecules results in flow of heat.

  3. The cooler portion of the air surrounding a warmer part exerts a buoyant force on it.

  4. As the warmer part of the air moves, it is replaced by cooler air that is subsequently warmed up.

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Correct Option: A,B,C,D
Explanation:

A continuous flow of warmer and cooler parts of air is established in which the air molecules are responsible for flow of heat. As the warmer air molecules move up, they are replaced bu cooler air molecules.

For cooking the food, which of the following type of utensil is most suitable 

conduction in metals and non-metals thermal energy transfers physics

  1. High specific heat and low conductivity

  2. High specific heat and high conductivity

  3. Low specific heat and low conductivity

  4. Low specific heat and high conductivity

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Correct Option: C

Two walls of thickness $d _1$ and $d _2$, thermal conductivities $K _1$ and $K _2$ are in contact. In the steady state if the temperature at the outer surfaces are $T _1$ and $T _2$, the temperature are the common wall will be 

conduction in metals and non-metals thermal energy transfers physics

  1. $\dfrac{K _1T _1+K _2T _2}{d _1d _2}$

  2. $\dfrac{K _1T _1d _2+K _2T _2d _1}{K _1d _2+K _2d _1}$

  3. $\dfrac{K _1d _1T _1+K _2d _2T _2}{K _1d _1+K _2d _2}$

  4. $\dfrac{(K _1d _1+K _2d _2)T _1T _2}{T _1+T _2}$

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Correct Option: B
Explanation:

$\begin{array}{l} { k _{ 1 } }\dfrac { { { T _{ 1 } }-{ T _{ c } } } }{ { { d _{ 1 } } } } ={ k _{ 2 } }\dfrac { { { T _{ c } }-{ T _{ 2 } } } }{ { { d _{ 2 } } } }  \ where\, { T _{ c } }\, is\, \, common\, \, wall\, temperature,\, solving\, for\, \, { T _{ c } }\, we\, \, will\, get \ { T _{ C } }=\dfrac { { { T _{ 1 } }+\alpha { T _{ 2 } } } }{ { \alpha +1 } }  \ u\sin  g\, \, \alpha =\dfrac { { { d _{ 1 } } } }{ { { d _{ 2 } } } } \dfrac { { { k _{ 2 } } } }{ { { k _{ 1 } } } }  \ { T _{ c } }=\dfrac { { { T _{ 1 } }+\dfrac { { { d _{ 1 } } } }{ { { d _{ 2 } } } } \dfrac { { { k _{ 2 } } } }{ { { k _{ 1 } } } } { T _{ 2 } } } }{ { \dfrac { { { d _{ 1 } } } }{ { { d _{ 2 } } } } \dfrac { { { k _{ 2 } } } }{ { { k _{ 1 } } } } +1 } }  \ =\dfrac { { { T _{ 1 } }\left( { { d _{ 2 } }{ k _{ 1 } } } \right) +{ T _{ 2 } }{ d _{ 1 } }{ k _{ 2 } } } }{ { { d _{ 1 } }{ k _{ 2 } }+{ d _{ 2 } }{ k _{ 1 } } } }  \ Hence,\, the\, option\, B\, is\, the\, \, correct\, answer. \end{array}$

The area of cross - section of rod is given by $ A = a _0 (1 + \alpha x )  $ where $  A _{ 0 }\quad & \quad \alpha  $ are constant and x is the distance from one end If thermal conductivity of material is K. What is the thermal resistance of the rod if its length is 

conduction in metals and non-metals thermal energy transfers physics

  1. $ KA _{ 0 }\alpha \quad to\quad (1+a\ell _{ 0 }) $

  2. $ \frac { 1 }{ Ka _{ 0 }\alpha } \quad \ell n \quad (1+\alpha\ell _{ 0 })$

  3. $ \frac { \alpha }{ KA _{ 0 } } \quad \ell n\quad (1+a\ell _{ 0 }) $

  4. $ \frac { KA _{ 0 } }{ \alpha } \ell n(1+\alpha \ell _{ 0 })$

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Correct Option: B
Explanation:

$\begin{array}{l} A={ a _{ 0 } }\left( { 1+\alpha x } \right)  \ dR=\dfrac { { dx } }{ { KA } }  \ =\dfrac { { dx } }{ { K{ \alpha _{ 0 } }\left( { 1+\alpha x } \right)  } }  \ =R=\dfrac { 1 }{ { K{ a _{ 0 } } } } \int _{ 0 }^{ { l _{ 0 } } }{ \dfrac { { dx } }{ { 1+\alpha x } }  }  \ =\dfrac { 1 }{ { \alpha K{ a _{ 0 } } } } \ln { \left( { 1+\alpha { l _{ 0 } } } \right)  }  \ =\dfrac { 1 }{ { K{ a _{ 0 } }\alpha  } } \ln { \left( { 1+\alpha { l _{ 0 } } } \right)  }  \ Hence, \ option\, \, B\, \, is\, correct\, \, answer. \end{array}$

a container that suits the occurrence of an isothermal process should be made of 

conduction in metals and non-metals thermal energy transfers physics

  1. Copper

  2. Glass

  3. Wood

  4. Cloth

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Correct Option: A

The temperature of skin is $T _{skin} = 34^0C$ (somewhat less than the body temperature, $T _{body} = 37^0C$) and the ambient tempreature is $T _{room} = 24^0C$. The surface area of an adult is A $\simeq$ 1.85 $m^2$. Calculate the net heat loss of the person.

conduction in metals and non-metals thermal energy transfers physics

  1. 25 W

  2. 100 W

  3. 300 W

  4. 500 W

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Correct Option: A

Consider a compound slab consisting of two different materials having equal thickness and thermals conductivities K and $2K$ in series. The equilvalent conductivity of  the slab is

conduction in metals and non-metals thermal energy transfers physics

  1. $\frac{2}{3}K$

  2. $\sqrt {2K} $

  3. $3K$

  4. $\left( {\frac{4}{3}} \right)K$

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Correct Option: C

Pick the odd one out. Give scientifc reason for your answer:

conduction in metals and non-metals thermal energy transfers physics

  1. Conduction, convection, fusion, radiation.

  2. Iron, aluminimum, asbestos, copper

  3. Felt, paper, silver, wood

  4. Ventilation, land breeze, sea breeze, thermos flask

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Correct Option: A
Explanation:

Conduction, convection and radiation are the mode of heat transfer whereas fusion is the nuclear reaction.

So, option A is correct.

It is required to double the pressure of a gas contained in steel cylinder by heating. If the initial temperature of the gas is ${ 27 }^{ 0 }C$, the temperature upto which it the gas is to be heated is 

conduction in metals and non-metals thermal energy transfers physics

  1. ${ 327 }^{ 0 }C$

  2. ${ 273 }^{ 0 }C$

  3. ${ 108}^{ 0 }C$

  4. ${ 54 }^{ 0 }C$

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Correct Option: C

At zero Kelvin, Germenium is:-

conduction in metals and non-metals thermal energy transfers physics

  1. Superconductor

  2. Good conductor

  3. Insulator

  4. Semiconductor

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Correct Option: C