Tag: heat and heat transfer

Questions Related to heat and heat transfer

Name a metal among the following having highest heat conductivity .

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

  1. Silver

  2. Copper

  3. Aluminium

  4. Brass

Show answer
Correct Option: A
Explanation:
Following are the thermal conductivities of the following metals and alloys: ( in $wK/m$ )
$Silver-430 \\ Copper-400 \\ Aluminium-235 \\ Brass-109$
Order of thermal (heat) conductivity:
$Silver \gt Copper \gt Aluminium \gt Brass$
So, Silver has highest thermal conductivity

When we touch a steel rod and a paper simultaneously, we feel that the rod is colder because:

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

  1. iron being a good conductor conducts more heat from our body

  2. paper being a good conductor conducts more heat from our body

  3. more heat flows from the iron to our body

  4. more heat flows from the paper to our body

Show answer
Correct Option: A
Explanation:

When we touch a steel rod and a paper simultaneously in winter, we feel the rod is comparatively colder because steel being a good conductor of heat, heat from our hand flows to steel but there is no transfer of heat from our hand to paper as it is an insulator of heat. So we don't feel cold when we touch a paper but we do when we touch a steel rod.

A good insulator of heat is

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

  1. copper

  2. mercury

  3. trapped air

  4. iron

Show answer
Correct Option: C
Explanation:

A thermal conductor is a material that allows energy in the form of heat, to be transferred within the material, without any movement of the material itself. Eg. Metals.

An insulator is a material that does not allow a transfer of electricity or energy. Materials that are poor thermal conductors can also be described as being good thermal insulators.Eg. trapped air

Which of the following statement is true?

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

  1. Metals are bad conductors of heat

  2. In gases, heat is transferred by conduction

  3. In conduction, molecules move from hotter to colder parts transmitting energy

  4. Metals conduct heat better than the gases.

Show answer
Correct Option: D
Explanation:
Metals conduct heat better than gases.
Order of conduction of heat
Solid $\gt$ Liquid $\gt$ Gas

Which of the following are good conductors of heat?

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

  1. Metals

  2. Glass

  3. Water

  4. Wood

Show answer
Correct Option: A
Explanation:

Metals are generally good conductors of heat.
Non - metals are poor conductors of heat.

Which of the following is the very poor conductor of heat ?

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

  1. Water

  2. Metals

  3. Liquid other than water

  4. Steam

Show answer
Correct Option: A
Explanation:

Water is the poor conductor among all. As it is liquid and liquids generally have low heat conductivity than solids. Tighter the molecules are held, more the vibrational energy can transfer between them, heat is no more than vibrating molecules. If we talk about steam, its molecules are less tightly held. But it's important to note that we are talking here of heat conductivity not convection or radiation and contact surface area with heat source.

Assertion (A): Woolen clothes keep the body warm in winter
Reason (R): Air is bad conductor of heat

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

  1. Both A and R are true,

  2. Both A and R are false

  3. Both A and R are true, R is correct explanation of A

  4. Both A and R are true, R is not correct explanation of A

Show answer
Correct Option: C
Explanation:

Woollen clothes effectively separate the body from surrounding air by entrapping a layer of air.
Since both wool and air are bad conductors of heat on varying levels, it creates separation that keeps bodies warm.

Substances which allow heat to pass through them are called:

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

  1. Conductors

  2. Insulators

  3. Moderators

  4. None of these

Show answer
Correct Option: A
Explanation:

Conductors allow heat to pass through them through vibration of the molecules.

A coin is dipped in the molten wax in a glass tube. When we heat the upper part of the glass tube, the wax around the coil will not melt because:

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

  1. Wax has a very high melting point

  2. Wax is a good conductor of heat

  3. Glass is a good conductor of heat

  4. Wax or glass are bad conductors

Show answer
Correct Option: D
Explanation:

Glass is a bad conductor of heat hence the heat from the upper part of the glass tube will not transfer easily to the lower part. Having said that, even wax is a bad conductor of heat and won't melt easily. 

Mercury is a good conductor of heat.State true or false.

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

  1. True

  2. False

Show answer
Correct Option: A
Explanation:
Mercury is good conductor of heat. (True)
Thermal conductivity of mercury is $8.30W/mK$. This is the fact why it was used in classical, thermometers for measuring temperature.