Tag: conduction in metals and non-metals

Quizzes (0) Questions (26)

Questions Related to conduction in metals and non-metals

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.

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

A solid sphere and a hollow sphere of same material and size are heated to some temperature and allowed to cool in the same surroundings.If the temperature difference between each sphere and its surrounding is T, then:-

  1. The hollow sphere will cool at a faster rate for all values of T

  2. The solid sphere will cool at a faster rate for all values of T

  3. Both spheres will coll at the same rate for all values of T

  4. Both spheres will coll at the same rate only for small values of T
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

According to Newton's law of cooling, the rate of cooling depends on the surface area and emissivity. Since the spheres have the same material, size, and surroundings, they have the same surface area and emissivity, resulting in the same rate of cooling.