Tag: heat and heat transfer

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Questions Related to heat and heat transfer

Multiple choice physics transfer of heat heat and heat transfer heat energy transfer heat energy transfers fundamentals of heat transfer conduction

The outermost electrons are __________ and are called conduction electrons :

  1. not free to move in the atom

  2. bound to the protons

  3. static

  4. able to go to nearby atoms
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
The outermost electrons are able to go to nearby atoms and are called conduction electrons.
Yes the outermost shell electrons are able to go to nearby atoms only during bond formation (ionic bond). They are free or mobile electrons because of that they conduct electricity so they are called conduction electrons.
Multiple choice physics transfer of heat heat and heat transfer heat energy transfer heat energy transfers fundamentals of heat transfer conduction

Which material is a best conductor?

  1. silver

  2. porcelain

  3. rubber

  4. gold
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
Out of silver, porcelain, rubber, and gold; porcelain and rubber are non-metals i.e. insulators. So
Now out of silver and gold conductivity of silver ($62.1\times 10^6 siemens/m$) is more than that of gold ($44.2\times 10^6 siemens/m$)
Multiple choice physics transfer of heat heat and heat transfer heat energy transfer heat energy transfers fundamentals of heat transfer conduction

Which metal is a good conductor of heat?

  1. Gold

  2. Mercury

  3. Lead

  4. Alloys
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
As metals contain free electrons, it transfers the energy given in the form of heat rapidly but in non-metals, it takes time to heat. Gold is metal so it is a good conductor of heat and mercury, lead, alloys are non-metals so they are poor conductors of heat.


Multiple choice physics transfer of heat heat and heat transfer heat energy transfer heat energy transfers fundamentals of heat transfer conduction

Mud houses are cooler in summer and warmer in winter because

  1. mud is a good conductor of heat

  2. mud is a superconductor of heat

  3. mud is a bad conductor of heat

  4. none of these
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Mud is a bad conductor of heat. It does not allow the heat to transfer from house to atmosphere in winter and atmosphere to house in summer.

Multiple choice physics transfer of heat heat and heat transfer heat energy transfer heat energy transfers fundamentals of heat transfer conduction

In case of conductors and insulators, if an electric field is applied then conduction current density$\vec{(J)}$ is:

  1. in the direction of electron flow.

  2. in the direction of proton flow.

  3. in the direction of electric field.

  4. against the direction of electric field.
Reveal answer Fill a bubble to check yourself
B,C Correct answer
Explanation
Current density, $\overrightarrow { J } =\cfrac { I }{ \overrightarrow { A }  } $
Current flows in direction of flow of protons. And the direction of electric field is in the direction of flow of electrons.
And the direction of current density is in the direction of proton flow, so from above statements, current density is also in the direction of electric field.
Multiple choice physics thermal physics heat and heat transfer transfer of heat fundamentals of heat transfer

A person takes hot tea by pouring it into the saucer (plate) when one is in a hurry because he knows that

  1. The latent heat of steam is high and the tea will become cold quickly

  2. The evaporation increases with the increase in surface area and cooling of tea is faster

  3. Part of heat will be absorbed by the saucer (plate) and the tea will become cold quickly

  4. The high specific heat of water makes the tea cold quickly
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Evaporation is a surface phenomenon. By pouring tea into a saucer, the surface area exposed to the air increases, which significantly accelerates the rate of evaporation and consequently cools the liquid faster.

Multiple choice physics thermal physics heat and heat transfer transfer of heat fundamentals of heat transfer

A copper ball of mass $100\ gm $ is at a temperature $T$. It is dropped in a copper calorimeter of mass $100\ gm$, filled with $170\ gm $ of water at room temperature. Subsequently, the temperature of the system is found to be $75^{o}C$. $T$ is given by : 

  1. $825^{o}C$

  2. $800^{o}C$

  3. $885^{o}C$

  4. $1250^{o}C$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
Heat given $=$ Heat taken
$\left(100\right)\left(0.1\right))\left(T–75\right))=\left(100\right))\left(0.1\right))\left(45\right))+\left(170\right))\left(1\right))\left(45\right))$
$ 10\left(T−75\right))=450+7650=8100$
$T−75=810$
$T={885}^{\circ}$C
Multiple choice physics thermal physics heat and heat transfer transfer of heat fundamentals of heat transfer

There are two lead spheres, the ratio c being $1 : 2$. If both are at the same tempe then ratio of heat contents is

  1. $1 : 1$

  2. $1 : 2$

  3. $1 : 4$

  4. $1 : 8$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

We know that the heat content is proportional to the mass and specific heat capacity of the substance as well as temperature. As both the spheres are of the same material and are at the same temperature, heat content will be dependent on mass only.

$ m = \rho \times v$

where $ \rho $ is the density of the sphere and $v$ the volume.

And $ v $ = $ \dfrac {4 \pi r^3}{3} $

The given radius ratio is $ 1:2 $.

Hence heat contents ratio is in the ratio $1:8$

Multiple choice physics temperature and heat heat and heat transfer transfer of heat fundamentals of heat transfer

From below which are the good conductors of heat?

  1. Metals

  2. Plastic

  3. Paper

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

In conduction, heat is transferred by the vibrations of molecules. The density of metals is large, it means molecules are close to each other, because of that they can easily transfer the heat quickly through the whole conductor, besides this metals have electron sea, due to smaller size of electrons compared to metal ions, electrons can easily pass through the space between ions, thus transfer the heat. Therefore are good conductors of heat.