Physics

Thermal Properties and Thermodynamics

431 Questions

Thermal properties and thermodynamics questions evaluate concepts of heat transfer, thermal efficiency, and temperature variations. Problems involve calculating heat content, conductivity, and the performance of heat engines. This subject is regularly tested in physics sections across multiple competitive platforms.

Heat transfer calculationsThermal efficiencyBlack body radiationTemperature variationsRefrigeration performance

Thermal Properties and Thermodynamics Questions

Multiple choice principal and molar specific heats of gases isothermal and adiabatic processes specific heat capacity heat and thermodynamics physics

A solid copper sphere(density $\rho$ and specific heat c) of radius r at an initial temperature $200$K is suspended inside a chamber whose walls are at almost $0$ K. The time required to the temperature of sphere to drop to $100$ K is _________?

  1. $\dfrac{9r\rho c}{72\times 10^6\sigma}$sec.
  2. $\dfrac{7r\rho c}{72\times 10^6\sigma}$sec.
  3. $\dfrac{7r\rho c}{82\times 10^6\sigma}$sec.
  4. $\dfrac{19r\rho c}{72\times 10^7\sigma}$sec.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

This involves Stefan-Boltzmann law for cooling. The time taken to cool from T1 to T2 is derived by integrating the rate of heat loss. The correct coefficient for the given parameters leads to option B.

Multiple choice principal and molar specific heats of gases isothermal and adiabatic processes specific heat capacity heat and thermodynamics physics

Thermal efficiency $=$ .........................   or
$\displaystyle \frac{Heat  Utilised}{Heat  Produced}$

  1. $\displaystyle \frac{Q _4}{Q _T}$
  2. $Q _4 \times Q _T$
  3. $Q _4 + Q _T$
  4. $Q _4 - Q _T$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Thermal efficiency is defined as the ratio of useful heat output (Heat Utilised) to the total heat input (Heat Produced).

Multiple choice principal and molar specific heats of gases isothermal and adiabatic processes specific heat capacity heat and thermodynamics physics

Consider a classroom that is roughly  $5 { m } \times 10  { m } \times 3  { m }.$  Initially   ${ t } = 20 ^ { \circ }  { C }$  and  $ { P } = 1$ atm. There are  $50$  people in an insulated class loosing energy to the room at the average rate of  $150$  watt per person. How long can they remain in class if the body temperature is  $37 ^ { \circ } \mathrm { C }$  and person feels uncomfortable above this temperature. Molar heat capacity of air  $= ( 7 / 2 ) R.$

  1. $4.34$ minutes
  2. $5.73$ minutes
  3. $6.86$ minutes
  4. $7.79$ minutes
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The room volume is 150 m^3. Using PV=nRT, calculate the number of moles of air. The total heat added by 50 people is 50 * 150 W = 7500 J/s. The heat required to raise the air temperature from 20 C to 37 C is Q = n * Cv * delta T. Solving for time t = Q / Power gives approximately 4.34 minutes.

Multiple choice principal and molar specific heats of gases isothermal and adiabatic processes specific heat capacity heat and thermodynamics physics

A sphere of density $\rho$, specific heat capacity c and radius r, is hung by a thermally insulated thread in an enclosure which is kept at a temperature slightly lower than that of the sphere. The rate of change of temperature for the sphere depends upon the temperature difference between the sphere and the enclosure, and is proportional to then

  1. $\dfrac{c}{r^3 \rho}$
  2. $\dfrac{r^3 \rho}{c}$
  3. $r^3 \rho c$
  4. $\dfrac{1}{r \rho c}$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

$P. \dfrac{4}{3} \pi r^3 . c. \dfrac{dT}{dt} = e . 4 \pi r^2 \sigma (T - T _0)$
$\dfrac{dT}{dt} \propto \dfrac{1}{Prc}$

Multiple choice chemistry matter around us measurement of properties effect of temperature and pressure on states of matter general introduction: importance and scope of chemistry

If $T _1$ and $T _2$ are two temperatures, which of the following expressions will yield the same value whether both temperatures are given in Celsius or Kelvin?

  1. $T _1+T _2$
  2. $T _1-T _2$
  3. $T _1\times T _2$
  4. $\dfrac{T _1}{T _2}$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Temperature differences are the same in both Celsius and Kelvin scales because the size of one degree Celsius is equal to the size of one Kelvin. Thus, T1 - T2 remains constant regardless of the scale used.

Multiple choice chemistry matter around us measurement of properties effect of temperature and pressure on states of matter general introduction: importance and scope of chemistry

$1^{\circ}C$ rise in temperature is equal to rise of:

  1. ${ 1 }^{ 0 }F$
  2. ${ 9/5 }^{ 0 }F$
  3. ${ 5/9 }^{ 0 }F$
  4. ${ 33 }^{ 0 }F$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Solution:- (B) $\cfrac{9}{5} ℉$

As we now that,
$F  = \cfrac{9}{5} C + 32$
As the temperature is risen by $1 ℃$-
$C' = C + 1$
Therefore,
$F' = \cfrac{9}{5} \left( C + 1 \right) + 32$
$F' = \cfrac{9}{5}C + \cfrac{9}{5} + 32$
$\Rightarrow F' = \left( \cfrac{9}{5}C + 32 \right) + \cfrac{9}{5}$
$\Rightarrow F' = F + \cfrac{9}{5}$
Hence $1 ℃$ rise in temperature is equal to the rise in $\cfrac{9}{5} ℉$.

Multiple choice

Pasteurization is heating at

  1. 120∘C for 60 minutes

  2. 60∘−63∘C for 30 minutes

  3. 70∘C for 60 minutes

  4. 80∘C for 30 minutes
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Pasteurization is a heat treatment process used to kill pathogens in food products. The classic 'low temperature long time' (LTLT) method involves heating to 60-63 degrees Celsius for 30 minutes.

Multiple choice

In what direction does thermal energy always transfer?

  1. Always moves up

  2. Always moves down

  3. Low to High

  4. High to Low
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Thermal energy naturally flows from a region of higher temperature to a region of lower temperature until thermal equilibrium is reached. This is a fundamental principle of thermodynamics.

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.