Tag: temperature and heat

Questions Related to temperature and heat

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

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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.

Conduction is not possible in

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

  1. iron

  2. water

  3. vacuum

  4. aluminium

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Correct Option: C

A spherical black body of radius $(R)$ when heated to certain temperature and left in vaccum. cools at a rate $'x' $ Now a caity of radius $(R/2)$ is made concentrically from this sphere. The rate of cooling of the remaining sphere will be.....................

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

  1. $\cfrac { x }{ 8 } $

  2. $\cfrac { 7x }{ 8 } $

  3. $\cfrac { 8x }{ 8 } $

  4. $\cfrac { x }{ 7 } $

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Correct Option: A

A hollow copper sphere and a hollow copper cube, of same surface area and negligible thickness, are filled with warm water of same temperature and placed in an enclosure of constant temperature, a few degrees below that of the bodies. Then in the beginning:

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

  1. the rate of energy lost by the sphere is greater than that by the cube

  2. the rate of fall of temperature for sphere is greater than that for the cube.

  3. the rate of energy lost by the sphere is less than that by the cube

  4. the rate of fall of temperature for sphere is less than that for the cube.

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Correct Option: B

A spherical body of radius n. If its rate of cooling is R, then

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

  1. $R \propto \frac{1}{n}$

  2. $R \propto \frac{1}{n^2}$

  3. $R \propto n$

  4. $R \propto n^2$

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Correct Option: C

A copper block of mass $500gm$ and $Sp.$ Heat $0.1 cal/gm/^{o}{C}$ is heated from ${30}^{o}C$ to ${40}^{o}C$. Another identical copper block $B$ of same mass is heated from ${35}^{o}C$ to ${40}^{o}C$. The ratio of their thermal capacities is 

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

  1. $1:2$

  2. $2:1$

  3. $1:1$

  4. $1:4$

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Correct Option: C

Heat required to convert one gram of ice at $0^{ _-^0}C$ into steam at $100^{ _-^0}C$ is (given $L _{steam}$ = 536 cal/gm)-

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

  1. 100 calorie

  2. 0.01 kilocalorie

  3. 716 calorie

  4. 1 kilocaorie

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Correct Option: C

Air is filled at $60^o$C in a vessel of open mouth. The vessel is heated at temperature T so that $\dfrac{1}{4}$ th part of air escapes. Assuming volume of container remaining constant, find value of T. 

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

  1. $80^oC$

  2. $444^oC$

  3. $333^oC$

  4. $171^oC$

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Correct Option: D