Tag: temperature and heat

Quizzes (15) Questions (111)

Questions Related to temperature and heat

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

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 $Wm^{-1}$ $K^{-1}$

  1. $20^{\circ}C$

  2. $40^{\circ}C$

  3. $80^{\circ}C$

  4. $1000^{\circ}C$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Using H = kA(dT/L), 6000 = 200 * 0.75 * (dT/1). 6000 = 150 * dT, so dT = 40 C.

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

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:-

  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
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Rate of cooling dT/dt = (sigma * A * e * (T^4 - Ta^4)) / (m * c). For same mass and material, the body with the smallest surface area A cools the slowest. A sphere has the smallest surface area for a given volume/mass, so it takes the longest to cool.

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

The dimensional formula for coefficient of thermal conductivity is:

  1. $[MLTK]$

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

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

  4. $[ML{T^{ - 3}}{k^{ - 1}}]$
Reveal answer Fill a bubble to check yourself
D Correct answer
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.

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

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.....................

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

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

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

  4. $\cfrac { x }{ 7 } $
Reveal answer Fill a bubble to check yourself
A Correct answer
Multiple choice physics temperature and heat modes of heat transfer - conduction conduction heat and modes of heat transfer

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:

  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.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Rate of cooling dT/dt = (sigma * A * (T^4 - Ta^4)) / (m * c). For the same surface area A, the body with the smaller mass m will have a higher rate of temperature fall. A hollow sphere has less volume (and thus less mass) than a hollow cube of the same surface area.

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

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 

  1. $1:2$

  2. $2:1$

  3. $1:1$

  4. $1:4$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Thermal capacity is defined as mass * specific heat (m * c). Since both blocks have the same mass and are made of the same material (copper), their thermal capacities are identical, resulting in a 1:1 ratio.

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

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)-

  1. 100 calorie

  2. 0.01 kilocalorie

  3. 716 calorie

  4. 1 kilocaorie
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Heat = (m * L_fusion) + (m * c_water * dT) + (m * L_vaporization). For 1g: (1 * 80) + (1 * 1 * 100) + (1 * 536) = 80 + 100 + 536 = 716 calories.

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

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. 

  1. $80^oC$

  2. $444^oC$

  3. $333^oC$

  4. $171^oC$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Using PV = nRT, since P and V are constant, n1*T1 = n2*T2. If 1/4 escapes, n2 = 3/4 n1. So n1 * (60 + 273) = (3/4)n1 * (T + 273). 333 = 0.75 * (T + 273). 444 = T + 273, so T = 171 C.