Tag: transfer of heat

Questions Related to transfer of heat

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

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

  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.

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Correct Option: B,C
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.

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

physics thermal physics heat and heat transfer transfer of heat fundamentals of heat transfer

  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

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Correct Option: B

Heat flows as a result of difference in

physics thermal physics heat and heat transfer transfer of heat fundamentals of heat transfer

  1. Masses

  2. Weights

  3. Temperatures

  4. None of these

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Correct Option: C
Explanation:

Heat spontaneously flows from a hotter to a colder body. The rate at which energy is conducted as heat is a function of temperature. Hence heat flows as a result of temperature.

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 : 

physics thermal physics heat and heat transfer transfer of heat fundamentals of heat transfer

  1. $825^{o}C$

  2. $800^{o}C$

  3. $885^{o}C$

  4. $1250^{o}C$

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Correct Option: C
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

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

physics thermal physics heat and heat transfer transfer of heat fundamentals of heat transfer

  1. $1 : 1$

  2. $1 : 2$

  3. $1 : 4$

  4. $1 : 8$

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Correct Option: D
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 $1:8$

From below which are the good conductors of heat?

physics temperature and heat heat and heat transfer transfer of heat fundamentals of heat transfer

  1. Metals

  2. Plastic

  3. Paper

  4. Wood

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Correct Option: A
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.

Insulators have very high :

physics temperature and heat heat and heat transfer transfer of heat fundamentals of heat transfer

  1. boiling point

  2. melting point

  3. specific heat capacity

  4. freezing point

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Correct Option: C
Explanation:

The specific heat capacity of a substance is the amount of heat required to raise the temperature of unit mass of substance through $1^{o}$.

As the insulators don't allow the heat to pass through them easily, therefore a large amount of heat is required to raise their temperature through $1^{o}$ i.e. insulators have high specific heat capacity.

Define good conductors of heat.

physics temperature and heat heat and heat transfer transfer of heat fundamentals of heat transfer

  1. Substances that can easily melt are called good conductors of heat.

  2. Substances through which heat can pass easily are called good conductors of heat.

  3. Substances through which heat cannot pass easily are called good conductors of heat.

  4. Substances that cannot easily melt are called good conductors of heat.

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Correct Option: B
Explanation:

Good conductors of heat are substances through which heat can pass easily.

Why do insulators take larger time to heat up?

physics temperature and heat heat and heat transfer transfer of heat fundamentals of heat transfer

  1. They need more heat per every degree Celsius rise in temperature.

  2. They need more energy per every degree Celsius rise in temperature.

  3. They need more to perform more work per every degree Celsius rise in temperature.

  4. They need more heat per every degree Farenheit rise in temperature.

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Correct Option: A
Explanation:

Substances which don't allow heat to easily pass through them are known as insulators. Insulators have crystal structure of molecules, molecules are far from each other, compared to conductors. Hence, they cannot pass the heat easily through them, besides this insulators don't have free electrons to pass heat more quickly. Therefore, unit mass of an insulator requires more heat to raise its temperature by $1^{o}$ i.e. specific heat capacity of insulators is very high or we can say they need more heat per degree rise in temperature.

Substances which allow heat to pass through them easily are known as

physics temperature and heat heat and heat transfer transfer of heat fundamentals of heat transfer

  1. Insulators

  2. Conductors

  3. Semi Conductors

  4. None

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Correct Option: B
Explanation:

Substances which allows heat to pass through them easily are known as Conductors.

Substances which don't allow heat to pass through them easily are known as Insulators.
Substances which allows current to pass through them in some conditions are known as Semiconductors.