Tag: physics

Questions Related to physics

The dimensions of coefficient of thermal conductivity is:

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

  1. $M \ L^{.2} T^{.2} K^{.1}$

  2. $M \ L \ T^{.-3} K^{.-1}$

  3. $M \ L \ T^{.2} K^{.1}$

  4. $M \ L \ T^{.3} K$

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Correct Option: B
Explanation:

The dimension of coefficient of thermal conductivity is ${M^1}{L^1}{T^{ - 3}}{K^{ - 1}}$ 

Hence,
option $B$ is correct answer.

A wall has two layers A and B, each made of different material. Both the layers have the same thickness. The thermal conductivity of the material of A is twice that of B. Under thermal equilibrium, the temperature difference across the wall is $36^o$C. The temperature difference across the layer A is?

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

  1. $6^o$C

  2. $12^o$C

  3. $18^o$C

  4. $24^o$C

Show answer
Correct Option: B

a wall has two layers $A$ and $B,$ each made of  a different material.Both the layers have the same thickness.The thermal conductivity of the material of $A$ is twice that of $B.$ Under thermal equilibrium, the temperature difference across the wall is ${36^ \circ }C$ The temperature difference across the layer $A$ is  

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

  1. ${6^ \circ }C$

  2. ${12^ \circ }C$

  3. ${18^ \circ }C$

  4. ${24^ \circ }C$

Show answer
Correct Option: C

An aluminium meter rod of area of cross section $4cm^2$ with K=0.5 cal $g^{-1}$ $^oC^{-1}$ is observed that at steady state 360 cal of heat flows per minute.
The temperature gradient along the rod is

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

  1. $3^oC/cm$

  2. $6^oC/cm$

  3. $12^oC/cm$

  4. $20^oC/cm$

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Correct Option: A

A conducting ring lies fixed on a horizontal plane. If a charged nonmagnetic particle is released from a point (on the axis) at some height from the plane, then :

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

  1. an induced current will flow in clockwise or anticlockwise direction in the loop depending upon the nature of the charge

  2. the acceleration of the particle will decrease as it comes down

  3. the rate of production of heat in the ring will increase as the particle comes down

  4. no heat will be produced in the ring

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Correct Option: D

Ratio of radius of curvature of cylindrical emitters of same type is $1:4$ and their temp. are in ration $2:1$. Then ration of amount of heat emitted by them is-(For Cylinder length = radius);-

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

  1. 2:1

  2. 1:1

  3. 4:1

  4. 1:4

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Correct Option: B

If the coefficient of conductivity of aluminium is $0.5cal/cm-sec-^oC,$ then in order to conduct $10cal/sec-cm^2$ in the steady state, the temperature gradient in aluminium must be

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

  1. $5^oC/cm$

  2. $10^oC/cm$

  3. $20^oC/cm$

  4. $10.5^oC/cm$

Show answer
Correct Option: C

a rod of length 1 m having cross-sectional area 0.75 $m^{2}$ conduts heat at 6000 $Js^{-1}$. Then the temperature difference across the rod is, if k=200 $Wm^{-1}$ $K^{-1}$

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

  1. $20^{\circ}C$

  2. $40^{\circ}C$

  3. $80^{\circ}C$

  4. $1000^{\circ}C$

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Correct Option: B

A sphere, a cube and a thin circular plate all made of same substance and all have same mass. These are heated to $200^{o}C$ and then placed in a room. Then the:-

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

  1. Temperature of sphere drops to room temperature at last.

  2. Temperature of cube drops to room temperature at last.

  3. Temperature of thin circular plate drops to room temperature at last.

  4. Temperature of all the three drops to room temperature at the same time

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Correct Option: A

The dimensional formula for coefficient of thermal conductivity is:

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

  1. $[MLTK]$

  2. $[MLT{K^{ - 1}}]$

  3. $[MLT^{-1}{K^{ - 1}}]$

  4. $[ML{T^{ - 3}}{k^{ - 1}}]$

Show answer
Correct Option: D
Explanation:

The for the coefficient of thermal conductivity is

$K _{th}=\dfrac{Q\Delta x}{A\Delta T t}$
Dimensional formula of $K _{th}$
$[K _{th}]=\dfrac{[Heat].[length]}{[Area].[Temperature].[time]}$
$[K _{th}]=\dfrac{[ML^2T^{-2}].[L]}{[L^2].[K].[T]}$
$[K _{th}]=[MLT^{-3}K^{-1}]$

The correct option is D.