Tag: modes of heat transfer - conduction

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Questions Related to modes of heat transfer - conduction

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

Three rods of identical cross-sectional area and made from the same metal from the sides of an isosceles triangles ABC, right-angled at B. The point A and B are maintained at temperatures T and $(\sqrt{2})$T respectively. In the steady state, the temperature of the point C is $T _C$. Assuming that only heat conduction takes place, $T _C/T$ is?

  1. $\dfrac{1}{2\left(\sqrt{2}-1\right)}$

  2. $\dfrac{3}{\sqrt{2}+1}$

  3. $\dfrac{1}{\sqrt{3}\left(\sqrt{2}-1\right)}$

  4. $\dfrac{1}{\sqrt{2}+1}$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Using the steady-state heat flow condition (sum of heat currents at junction C is zero), the heat currents from A to C and B to C must balance. Given the geometry and thermal resistance, the calculation leads to the ratio 3/(sqrt(2)+1).

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.