Tag: heat and heat transfer

Questions Related to heat and heat transfer

State True or False :
Good conductors of heat are also good conductors of electricity. 

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

  1. True

  2. False

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Correct Option: B
Explanation:

Usually, good conductors of heat are also good conductors of electricity. However, this is not always true. One of the exceptions is mica. Mica is good conductor of heat but bad conductor of electricity.

Conductors become hot easily because they have:

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

  1. high specific capacity

  2. low specific heat capacity

  3. high freezing point

  4. low freezing point

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Correct Option: B

In general, metals have very low :

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

  1. Boiling Point

  2. Freezing Point

  3. Melting Point

  4. Specific Heat Capacity

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Correct Option: D
Explanation:

In conduction, heat is transferred by the vibrations of molecules. The density of conductors is large, it means molecules are close to each other, because of that they can easily transfer the heat quickly through the whole conductor, therefore unit mass of conductors require small heat to raise their temperature through $1^{o}$ i.e. conductors have very low specific heat. 

Specific heat capacity is ______ for conductors of heat and _______ for insulators of heat.

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

  1. low, low

  2. low, high

  3. high, high

  4. high, low

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Correct Option: B
Explanation:

$Q=ms\Delta T$,

where 
$Q: \text{the amount of heat delivered to a body}$
$m: \text{mass of the body}$
$s: \text{specific heat capacity of the body}$
$\Delta T: \text{Change in temperature of the body}$

If $Q\ \text{and}\ m$ are constant, 
$\Delta T \propto \dfrac{1}{s}$

So for small $s, \Delta T$ is more and hence it is better conductor of heat.

Conductors require __________ heat energy to get heated.

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

  1. More

  2. Same

  3. Less

  4. neutral

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Correct Option: C
Explanation:

Conductors have very low specific heat capacity (c) , therefore heat required (Q) to raise their temperature to a certain range is also less by the following relation: $Q\propto c$

Graphite is a conductor of electricity because

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

  1. it has free valence electrons.

  2. it is a non-metal form of Carbon.

  3. it is an allotrope of Carbon.

  4. Both A and B.

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Correct Option: A
Explanation:
Graphite is a conductor of electricity because it has free valence electrons.
Graphite displays the property of both metal and non-metal. Like a metal, graphite is good conductor of electricity due to mobility of electrons in outer valence shells.

Examples of non-conductors include

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

  1. sulphur.

  2. phosphorus.

  3. wood.

  4. all of these.

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Correct Option: D
Explanation:

Sulphur, Phosphorus, Wood are non-conductors of electricity due to no presence of free electrons in outermost shell.

Easy to shape materials like ceramics are used as

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

  1. conductors.

  2. insulators.

  3. electrodes.

  4. catalysts.

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Correct Option: B
Explanation:
Glass, tiles, pottery, porcelain, brick, cement etc. are ceramics.
They are obviously insulators of heat.

Overhead cables are insulated from pylons through

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

  1. plastic.

  2. ceramics and glass.

  3. rubber.

  4. PVC.

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Correct Option: B
Explanation:
Examples of ceramics are clay, bricks, tiles, glass, and cement.
Overhead cable is insulated from pylons through ceramics and glass.
The overhead power lines that are supported by pylons are not covered in insulating materials. However, ceramics or glass insulators are fitted between pylons and wires. This stops electricity flowing down the metal pylons to the ground, where it could hurt or even kill people or animals.

In conductors outer electrons :

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

  1. are not tightly bound to the nucleus

  2. are tightly bound to the nucleus

  3. never becomes free electrons

  4. are always free to move

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Correct Option: A
Explanation:

Conductors can easily conduct electricity because they are loosely bound to the nucleus and they are not engaged in chemical bonding. Conductors have free electrons.