Tag: temperature and heat

Questions Related to temperature and heat

The number of quanta of radiation of frequency $4.98 \times {10^{14}}{s^{ - 1}}$ required to melt 100 g of ice are (latent heat of melting of ice is 33 joule per g):

physics temperature and heat modes of heat transfer - conduction conduction heat and modes of heat transfer

  1. ${10^{20}}$

  2. ${10^{22}}$

  3. ${10^{24}}$

  4. $6.023 \times {10^{21}}$

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Correct Option: B
Explanation:

$1g$ requires $33J$. So, $100g$ will require $3300J$ heat.

Total quanta, 
E=hv
$=6.62\times { 10 }^{ -34 }\times 4.98\times { 10 }^{ 14 }\ =32.97\times { 10 }^{ -20 }$
$100g$ of ice will require=$\dfrac { 3300 }{ 32.97\times { 10 }^{ -20 } } =100.09$
$100$quantal=${ 10 }^{ 22 }J$

Two rods of the same length and diameter having thermal conductivities ${K _1}\,{K _2}$ are joined in parallel. The equivalent thermal conductivity of the combination is:

physics temperature and heat modes of heat transfer - conduction conduction heat and modes of heat transfer

  1. $\dfrac{{{K _1}{K _2}}}{{{K _1} + {K _2}}}$

  2. ${{K _1} + {K _2}}$

  3. $\dfrac{{{K _1} + {K _2}}}{2}$

  4. $\sqrt {{K _1}{K _2}} $

Show answer
Correct Option: A
Explanation:

$\dfrac{1}{{{K _{eq}}}} = \dfrac{1}{{{K _1}}} + \dfrac{1}{{{K _2}}}$

$\boxed{{K _{eq}} = \dfrac{{{K _1}{K _2}}}{{{K _1} + {K _2}}}}$

A cylinder of radius $R$ made of a material of thermal conductivity $K _1$ is surrounded by a cylindrical shell of inner radius $R$ and outer radius $2R$ made of a material of thermal conductivity $K _2$. The two ends of the combined system are maintained at two different temperatures. There is no loss of heat across the cylindrical surface and the system is in steady state. The effective thermal conductivity of the system is?

physics temperature and heat modes of heat transfer - conduction conduction heat and modes of heat transfer

  1. $K _1+K _2$

  2. $\dfrac{K _{1}+3K _{2}}{4}$

  3. $\dfrac{K _{1}+8K _{2}}{9}$

  4. $\dfrac{8K _{1}+K _{2}}{9}$

Show answer
Correct Option: A,C

In order that the heat flows one part of a solid to another part, what is required ?

physics temperature and heat modes of heat transfer - conduction conduction heat and modes of heat transfer

  1. uniform density

  2. temperature gradient

  3. density gradient

  4. uniform temperature

Show answer
Correct Option: B
Explanation:

As heat flows from higher temperature to lower temperature, so a temperature gradient is required.

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

Show answer
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

Show answer
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.

Show answer
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.

Show answer
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

Show answer
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. 

Substances which do not allow heat to easily pass through them are known as

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

  1. Conductors

  2. Insulators

  3. Semi Conductors

  4. None

Show answer
Correct Option: B
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.