Tag: conduction

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Questions Related to conduction

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

If $K$ denotes coefficient of thermal conductivity, $d$ the density and $C$ the specific heat, the unit of $X$, where $X = K/dc$, will be

  1. $cm\space sec$

  2. $cm^2\space sec^{-2}$

  3. $cm \space sec^{2}$

  4. $cm^2 \space sec^{-1}$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The Units of the respective quantities in SI are:

  • $[K] = J(mKs)^{-1}$
  • $[\rho] = kg(m)^{-3}$
  • $[c] = J(kgK)^{-1}$
$[X] = \dfrac{[K]}{[\rho] [c]} = \dfrac{J(mKs)^{-1}}{(kg(m)^{-3})(J(kgK)^{-1})}$
$[X] = m^{2}s^{-1}$ or in CGS $cm^{2}s^{-1}$

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

A body of length 1 m have an area of cross-section as 0.75 $m^{2}$. If rate of heat conduction of the body is 6000 J/s and coefficient of thermal conductivity is 200 $Jm^{-1}$ $K^{-1}$, then the temperature difference between the two ends of the body is

  1. $30^{\circ}C$

  2. $20^{\circ}C$

  3. $40^{\circ}C$

  4. $80^{\circ}C$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Using the formula Q/t = kA(dT/dx), where Q/t = 6000, k = 200, A = 0.75, and dx = 1. Rearranging gives dT = (Q/t * dx) / (kA) = (6000 * 1) / (200 * 0.75) = 6000 / 150 = 40 degrees C.

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

Equal temperature difference exists between the ends of two metallic rods $1 $ and $2$ of length. Their thermal conductivities are $K _1$ and $K _2$ and cross sectional areas represents $A _1$ and $A _2$. The condition for equal rate of heat transfer is:

  1. $K _1A _2=K _2A _1$

  2. $K _1A _1=K _2A _2$

  3. $K _1A _1^2=K _2A _2^2$

  4. $K _1^2A _2=K _2^2A _1$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
Equal temperature difference exists between the two metallic rods 1 and 2.
The heat transfer$=\dfrac{KA \Delta T}{l}$
For equal rate of heat transfer,
$\dfrac{K _1 A _1 \Delta T}{l}=\dfrac{K _2A _2 \Delta T}{l}$
$K _1A _1=K _2A _2$
The correct option is B.
Multiple choice physics temperature and heat modes of heat transfer - conduction conduction heat and modes of heat transfer

Conduction of heat is possible:

  1. when the bodies are apart from each other

  2. when the bodies have same temperature and in thermal contact

  3. when they have different temperatures maintaining distance between them

  4. bodies should be in contact and should have different temperatures
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Conduction is only possible when the bodies in contact have a temperature difference.

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

More energetic molecules of a body transfer some of their energy to other molecules, without any change in their position in:

  1. conduction

  2. convection

  3. radiation

  4. none of these
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Conduction is defined as the process of transferring heat from molecule to molecule, without the actual movement of molecules.

Here, more energetic molecules of a body transfer some of their energy to other molecules, without any change in their position.

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

The thermal conductivity of the plate depends upon

  1. the temperature difference between the two sides

  2. the thickness of the plate

  3. the area of the plate

  4. nature of the material
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Thermal conductivity of any object depends solely on the material of the object.
It is an intrinsic property and is independent on dimensions/mass/etc of the body.
For example, all iron rods will have same thermal conductivity.
All copper rods will have same thermal conductivity.
But, thermal conductivity of iron rod will be different from that of copper rod.

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

Which of the following qualities are best suited for handling a cooking utensil?

  1. high specific heat and low thermal conductivity

  2. high specific heat and high thermal conductivity

  3. low specific heat and low thermal conductivity

  4. low specific heat and high thermal conductivity
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

High specific heat means high energy required to increase temperature.
Hence for a given amount of energy, temperature would be less for high specific heat.
Low conductivity means heat is not conveyed to all portions of the conductor easily.
Hence, handling the instrument would be easy.