Physics

Thermal Properties and Thermodynamics

380 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 physics heat energy transfers heat and heat transfer heat energy transfer transfer of heat

A metal cylinder of mass 0.5 kg is heated electrically by a 12 W heater in a room and cylinder temperature rises uniformly to $ 25^oC in 5 min $ excess temperature surroundings,

  1. The rate of loss of heat of the cylinder to surrounding at $ 20^oC $ is 2 W
  2. The rate of loss heat of the cylinder to surrounding at $ 45^oC $ is 12 W
  3. Specific heat capacity of metal is $ \frac {240}{Ib(3/2)} $

  4. None of these
Reveal answer Fill a bubble to check yourself
B Correct answer
Multiple choice physics heat energy transfers heat and heat transfer heat energy transfer transfer of heat

In the Ingen Hausz's experiment, the wax melts up to lengths $10cm$ and $25cm$ on two identical rods of different materials. The ratio of thermal conductivities of the two materials is

  1. $1:6.25$
  2. $6.25:1$
  3. $1: $$\sqrt{2.5}$
  4. $1:2.5$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

In the Ingen Hauszs experiment, as rate of heat transfer is constant
$\dfrac { { K } _{ 1 } }{ { K } _{ 2 } } =\dfrac { { l } _{ 1 } }{ { { l } _{ 2 } } } $
So, putting the value in above formula's we find
$\dfrac{{K} _{1}}{{K} _{2}}=\dfrac{10}{25}=\dfrac{1}{2.5}$

Multiple choice physics heat energy transfers heat and heat transfer heat energy transfer transfer of heat

Two blocks of steel A and B, A being two times heavier than B, are at 40$^o$C. The ratio of heat content of A to B is:

  1. 1

  2. 4

  3. 2
  4. $\displaystyle \frac{1}{2}$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
Let the mass of block B be $m$.
So, mass of block A is $2m$
Both are made of steel, so, both has same specific heat capacity (let 'S')

So, $\cfrac{Heat\;Capacity\;(A)}{Heat\;Capacity\;(B)}=\cfrac{2ms}{1ms}=2$
Multiple choice chemistry chemical thermodynamics system and surroundings introduction to thermodynamics basics of thermodynamics

Temperatures of two hot bodies $B _{1}$ and $B _{2}$ are $100^{\circ}C$ and $80^{\circ}C$ respectively. The temperature of surrounding is $40^{\circ}C$. At $t = 0$, the ratio of rates of cooling of the two bodies (liquid) $R _{1} : R _{2}$ will be:

  1. $3 : 2$
  2. $5 : 4$
  3. $2 : 1$
  4. $4 : 5$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Rate of cooling=$\cfrac { dQ }{ dt } \propto \quad \Delta T$ 

$\therefore \cfrac { { R } _{ 1 } }{ { R } _{ 2 } } =\cfrac { { \Delta T } _{ 1 } }{ { \Delta T } _{ 2 } } =\cfrac { 100-40 }{ 80-40 } =\cfrac { 60 }{ 40 } =\cfrac { 3 }{ 2 } $

Multiple choice chemistry chemical thermodynamics system and surroundings introduction to thermodynamics basics of thermodynamics

The work done in an open vessel at $300$K, when $112g$ iron reacts with dilute $HCl$ to give $FeCl _2$, is nearly:

  1. $1.1$ kcal
  2. $0.6$ kcal
  3. $0.3$ kcal
  4. $0.2$ kcal
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
The reaction involved is:
$Fe+2HCl \rightarrow FeCl _2+H _2$
Atomic mass of $Fe=56 g/mol $
Thus, 56 g of Iron reacts with 2 moles of HCl to give one mole of Hydrogen gas.
Initial volume of $H _2$ gas = $V _1 = 0$
Final volume of $H _2$ gas=$ V _2$
Using ideal gas law:$PV = n R T$
where n=mass/molar mass, R=8314 J/K/mol and given that T=300 K
$PV _2 = (112/56) \times 8.314 \times 300 = 4988.4J$
Work done $= -P \Delta V=-P(V _2 - V _1) =-P V _2 = -4988.4J$
negative work done is work of expansion.
since 4184 J=1 kcal
thus $4988.4 J=1.19 kcal$ of work is done by the system.
Multiple choice chemistry chemical thermodynamics system and surroundings introduction to thermodynamics basics of thermodynamics

An open vessel containing air is heated from 300 K to 400 K. The fraction of air originally present which goes out of it is:

  1. 3/4

  2. 1/4

  3. 2/3

  4. 1/8
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
 
According to ideal gas equation
$PV = nRT$
$\Rightarrow \; n \propto \cfrac{1}{T}$
$\Rightarrow \; \cfrac{{n} _{1}}{{n} _{2}} = \cfrac{{T} _{2}}{{T} _{1}}$
Given that:-
${n} _{1} = 1$ 
${T} _{1} = 300K$, 
${T} _{2} = 400K$ 
${n} _{2} = ?$
$\therefore \; \cfrac{1}{{n} _{2}} = \cfrac{400}{300}$
${n} _{2} = \cfrac{3}{4}$
The fraction of air present in the vessel after heating ${n} _{2} = \cfrac{3}{4}$
The fraction of air which goes out of the vessel $= 1 - \cfrac{3}{4} = \cfrac{1}{4}$
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.