Tag: thermal energy transfers

Quizzes (4) Questions (47)

Questions Related to thermal energy transfers

Multiple choice physics transfer of heat applications of convection convection thermal energy transfers

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

  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.
Reveal answer Fill a bubble to check yourself
A,B,C,D Correct answer
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.

Multiple choice conduction in metals and non-metals thermal energy transfers physics

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 

  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. $\dfrac{(K _1d _1+K _2d _2)T _1T _2}{T _1+T _2}$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

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

Multiple choice conduction in metals and non-metals thermal energy transfers physics

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 

  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 })$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

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

Multiple choice conduction in metals and non-metals thermal energy transfers physics

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

  1. Copper

  2. Glass

  3. Wood

  4. Cloth
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

An isothermal process requires the system to maintain a constant temperature. A good thermal conductor like copper allows heat to flow easily between the system and the surroundings to maintain that temperature.

Multiple choice conduction in metals and non-metals thermal energy transfers physics

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.

  1. 25 W

  2. 100 W

  3. 300 W

  4. 500 W
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Heat loss can be estimated using Newton's Law of Cooling or basic heat transfer principles. Given the temperature difference (34-24 = 10 degrees) and surface area, the power loss is roughly 25-100W depending on the heat transfer coefficient. 25W is a common textbook answer for this specific problem setup.

Multiple choice conduction in metals and non-metals thermal energy transfers physics

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

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

  2. $\sqrt {2K} $

  3. $3K$

  4. $\left( {\frac{4}{3}} \right)K$
Reveal answer Fill a bubble to check yourself
C Correct answer
Multiple choice conduction in metals and non-metals thermal energy transfers physics

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

  1. Conduction, convection, fusion, radiation.

  2. Iron, aluminimum, asbestos, copper

  3. Felt, paper, silver, wood

  4. Ventilation, land breeze, sea breeze, thermos flask
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

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

So, option A is correct.

Multiple choice conduction in metals and non-metals thermal energy transfers physics

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 

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

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

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

  4. ${ 54 }^{ 0 }C$
Reveal answer Fill a bubble to check yourself
C Correct answer
Multiple choice conduction in metals and non-metals thermal energy transfers physics

At zero Kelvin, Germenium is:-

  1. Superconductor

  2. Good conductor

  3. Insulator

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

Germanium is a semiconductor. At zero Kelvin, there is insufficient thermal energy to excite electrons across the band gap, meaning it behaves as an insulator.