Tag: conduction in metals and non-metals

Questions Related to conduction in metals and non-metals

A slab consists of two parallel layers of two difference materials of same thickness and having thermal conductivities $K _1$ and $K _2$. The equivalent thermal conductivity K of the slab is-

conduction in metals and non-metals thermal energy transfers physics

  1. $K _1+K _2$

  2. $\frac{2K _1K _2}{K _1+K _2}$

  3. $\frac{K _1+K _2}{K _1K _2}$

  4. $K _1K _2$

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Correct Option: A

Which of the following represent practical uses each of good conductors of heat?

conduction in metals and non-metals thermal energy transfers physics

  1. Cooking vessels are coated with copper at the base so as to readily absorb heat energy and get the food cooked quickly, thus saving time and fuel

  2. Mercury is used as a thermometric liquid as it is a good conductor of heat

  3. Cooling coils of refrigerators and air-conditioners are made of copper as they easily conduct away the heat 

  4. None of the above

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Correct Option: A,B,C
Explanation:
Cooking vessel are coated with copper at base, so as to readily absorb heat and get food cooked quickly thus saving the fuel and time as copper is good conductor of heat and it has comparatively more thermal conductivity.

Mercury is used in thermometer as it is good conductor of heat; it expands on heating accordingly.

Cooling coils of refrigerators and air-conditioners are mode of copper as they easily conduct away the heat. As copper has high thermal conductivity; it absorbs heat more quickly and in that coils, coolants are present to absorb heat.

On a cold morning, a metal surface in touching is felt colder than a wooden surface, because the metal has:

conduction in metals and non-metals thermal energy transfers physics

  1. low thermal condutivity

  2. high thermal conductivity

  3. high specific heat

  4. low specific heat

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Correct Option: B
Explanation:

Metal appears cool on touching because heat flows from body (at higher temperature) to iron (at lower temperature). This can happen only when metal conducts heat. Wooden surface does not feel cool as it is non-conductor of heat.

On a cold morning, a metal surface will feel colder to touch than a wooden surface, because:

conduction in metals and non-metals thermal energy transfers physics

  1. metal has high specific heat

  2. metal has high thermal conductivity

  3. metal has low specific heat

  4. metal has low thermal conductivity

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Correct Option: B
Explanation:

The metal has high thermal conductivity, i.e., they conduct heat faster. and also metal is a good conductor of heat. Hence, it takes away your body heat as you touch it and which makes your body temperature to drop, therefore you feel the coldness when you touch a piece of metal.

Statement-1
On a chilly day, the metallic cap of a pen feels much colder than the plastic body although both are at the same (room) temperature.
Statement-2
Metal has a higher coefficient of thermal conductivity than plastic.

conduction in metals and non-metals thermal energy transfers physics

  1. Statement-1 is true, Statement-2 is true and Statement-2 is the correct explanation for Statement- 1

  2. Statement-1 is true, Statement-2 is true but Statement-2 is not the correct explanation for Staement-1

  3. Statement-1 is true, Statement-2 is false.

  4. Statement-1 is false, Statement-2 is true.

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Correct Option: A
Explanation:

On the chilly day the room temperature is lower than our body temperature.Since metal is better conductor than plastic when we touch the metal cap and the plastic body of a pen,heat from our finger will flow more to the metal body as compare to plastic body. Hence option (A) is correct.

Metals are good conductors of heat because.

conduction in metals and non-metals thermal energy transfers physics

  1. They contain large number of free electrons

  2. Their atoms are relatively apart.

  3. Their atoms collide frequently.

  4. They have reflecting surfaces.

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Correct Option: C