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 conduction in metals and non-metals thermal energy transfers physics

A semicircular rod is joined at its end to a straight rod of the same material and the same cross-sectional area. The straight rod forms a diameter of the other rod. The junctions are maintained at different temperatures. Find the ratio of the heat transferred through a cross-section of the semicircular rod of the heat transferred through a cross-section the straight rod in the given time.

  1. $\dfrac 2\pi$
  2. $\dfrac 1\pi$
  3. $\dfrac 1{2\pi}$
  4. $\dfrac \pi2$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Heat flow rate is proportional to cross-sectional area and inversely proportional to length. For a semicircular rod of radius R, the length is pi*R and area is A. For the straight diameter rod, length is 2R and area is A. The ratio of heat flow (H_semi / H_straight) = (K*A*dT / (pi*R)) / (K*A*dT / (2*R)) = 2/pi.

Multiple choice conduction in metals and non-metals thermal energy transfers physics

Bimetallic thermostat consists two metals of different thermal co-efficient thermostat always bends towards material having
(i)large thermal expansion on heating 
(ii)large thermal expansion on cooling
(iii)small thermal expansion on heating
(iv)small thermal expansion on cooling

  1. I only

  2. II only

  3. III and II only

  4. I and IV only
Reveal answer Fill a bubble to check yourself
C Correct answer
Multiple choice conduction in metals and non-metals thermal energy transfers physics

A heat engine takes steam at $200^oC$ and after doing work exhausts it directly into air at $100^oC$. Calculate the percentage of heat which is wasted.

  1. $58.86$
  2. $68.86$
  3. $48.86$
  4. $78.86$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The maximum theoretical efficiency of a heat engine is given by the Carnot efficiency formula: Efficiency = 1 - (T_sink / T_source). Converting temperatures to Kelvin: T_source = 200 + 273 = 473 K and T_sink = 100 + 273 = 373 K. Efficiency = 1 - (373 / 473) = 1 - 0.7886 = 0.2114 or 21.14 percent, meaning the percentage of heat wasted is 100 - 21.14 = 78.86 percent.

Multiple choice conduction in metals and non-metals thermal energy transfers physics

Two angular blocks A and B different metal have same length and same area of cross-section . they are kept in such a way that their cross-sectional area touch each other. the temperature at one end of A is $ 100^0 $ C and that of B at the other end is $0^0 C $ C . if the ratio of their conductivity is 1:3 then under steady state, the temperature of the junction in contact will be:-

  1. $ 25^0 C $
  2. $ 50^0 C $
  3. $ 75^0 C $
  4. $ 100^0 C $
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

In steady state, the rate of heat flow through block A equals that through block B. Using the conduction formula (K * A * deltaT / L), since lengths and areas are equal, K1 * (100 - T) = K2 * (T - 0). Given K1:K2 = 1:3, 1 * (100 - T) = 3 * (T - 0), which gives 100 - T = 3T, resulting in 4T = 100 and T = 25 degrees Celsius.

Multiple choice conduction in metals and non-metals thermal energy transfers physics

On heating one end of a rod, the temperature of the whole rod will be uniform when the :

  1. $k $ $ = 1$
  2. $k $ $ = 0$
  3. $k $ $ = 100$
  4. $k $ $ = \infty $
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

If temperature of whole rod is same, it means that heat is being conducted from one end to other infinitely fast. This is possible only when thermal conductivity is infinite.

Multiple choice conduction in metals and non-metals thermal energy transfers physics

A slab consists of two parallel layers of two difference materials of same thickness and having thermal conductivities $K _1$ and $K _2$. The equivalent thermal conductivity K of the slab is-

  1. $K _1+K _2$
  2. $\frac{2K _1K _2}{K _1+K _2}$
  3. $\frac{K _1+K _2}{K _1K _2}$
  4. $K _1K _2$
Reveal answer Fill a bubble to check yourself
A Correct answer
Multiple choice physics heat energy transfers heat energy heat, internal energy and work internal energy

The temperature inside a refrigerator is $t _2$ $^0C$ and the room temperature is $t _1$ $^0C$. The amount of heat delivered to the room for each joule of electrical energy consumed ideally will be   

  1. $\frac{t _1}{t _1 - t _2}$
  2. $\frac{t _1 + 273}{t _1 - t _2}$
  3. $\frac{t _2 + 273}{t _1 + t _2}$
  4. $\frac{t _1 + t _2}{t _1 + 273}$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The coefficient of performance (COP) for a heat pump is defined as Q_h / W. In terms of absolute temperatures (Kelvin), the heat delivered to the room for each unit of work is T_1 / (T_1 - T_2), where T_1 and T_2 are in Kelvin.

Multiple choice physics heat energy transfers heat energy heat, internal energy and work internal energy

A refrigerator has to transfer an average of $263J$ of heat per second from the temperature $-10^oC$ to $25^oC.$ The average power consumed, if no energy is lost is 

  1. $100W$
  2. $7.5W$
  3. $25W$
  4. $35W$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The coefficient of performance (COP) of a refrigerator is given by COP = T2 / (T1 - T2). Temperatures in Kelvin are T2 = -10 + 273 = 263 K and T1 = 25 + 273 = 298 K, so T1 - T2 = 35 K. Thus, COP = 263 / 35. Power = Q2 / COP = 263 / (263 / 35) = 35 W.

Multiple choice physics heat energy transfers heat energy heat, internal energy and work internal energy

Hailstone at $0^{o}C$ falls from a height of $1\ km$ on an insulating surface converting whole of its kinetic energy into heat. What part of it will melt ? $(g=10\ m/s^{2}$)

  1. $\dfrac{1}{33}$
  2. $\dfrac{1}{8}$
  3. $\dfrac{1}{33}\times 10^{-4}$

  4. All of it will melt
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Given:

The height from which the Hailstone falls is $1\ km$.

The energy lost by the hailstone is the potential energy and as it falls, this energy converts into heat energy. This heat energy is utilized in melting the hailstone.

So, the part of the hailstone melted is given by equating the potential energy to the latent heat of fusion.
$mgh=KmL$
$\because$ Latent heat of ice $=3.36\times 10^{5}J/kg$

$\Rightarrow K=\dfrac{gh}{L}$

$=\dfrac{10\times 1000}{3.36\times 10^{5}}$

$=\dfrac{1}{33}$

Multiple choice physics heat energy transfers heat energy heat, internal energy and work internal energy

Two blocks of steel A and B of the same shape and size, A being two times heavier than B, are at $40^{\circ}C$. 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

The correct answer is option(C).

We know,
$Q=mC\Delta T$
Here Specific heat and raise in temperatures are equal.
And, given $2m _A=m _B$
So, the ratio of heat content can be,
$\dfrac {Q _1}{Q _2}=\dfrac {m _AC\Delta T}{m _BC\Delta T}=\dfrac {m _A}{m _B}=\dfrac 21=2$

Multiple choice physics measurement and effects of heat sources of heat introduction to heat measuring temperature

Out of the metal balls of same diameter one is solid and other is hollow. Both are heated to the same temperature at $300^{0}C$ and then allowed to cool in the same surroundings then rate of loss of heat will be:

  1. More for hollow sphere

  2. More for solid sphere

  3. Same for both

  4. None of the above
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The rate of loss of heat depends on the surface area and the emissivity. For a hollow sphere and a solid sphere of the same diameter, the surface area is identical. However, the hollow sphere has less mass, meaning it has a lower heat capacity and will cool faster.

Multiple choice evs - i methods of preserving food food spoilage and food preservation food poisoning and food preservation methods food spoilage, adulteration and preservation

Pasteurization is heating at

  1. $120^{0}$C for 60 minutes
  2. 60-$70^{0}$C for 30 minutes
  3. $70^{0}$'C for 60 minutes
  4. $80^{0}$C for 30 minutes
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

In the classic pasteurization treatment of milk, the milk was exposed to a temperature of about $63^{0}$C for 30 minutes. Most milk pasteurization today uses higher temperatures, at least $72^{0}$C, but for only 15 seconds. 


Multiple choice evs sources of water conservation of natural and energy resources energy conservation and sources reduce, recycle, reuse importance of the conservation of natural resources

How much radiant energy will an object emit if its temperature is at absolute zero?

  1. The maximum theoretical amount

  2. None

  3. The same as it would at any other temperature

  4. Depends on the chemical composition of the object
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

According to the third law of thermodynamics, at absolute zero, all molecular motion ceases, and therefore an object emits no radiant energy (thermal radiation).

Multiple choice zoology frog circulatory system in frog frog - digestive system, circulatory system, excretory system and reproductive system animal diversity - ii (phylum: chordata)

When a frog is transferred from $20^{o}$C to $30^{o}$C, its body temperature ________________.

  1. Falls to $15^{o}$C
  2. Rises to $30^{o}$C
  3. Falls to $12^{o}$C

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

Frogs are ectothermic (poikilothermic) animals, meaning their body temperature fluctuates with the ambient temperature of their environment.

Multiple choice physics heat and temperature anomalous expansion of water thermal expansion in solids, liquids and gases thermal expansion

There are two spherical balls A and B of the samematerial with same surface, but the diameter of A is half that of B. If Aand B are heated to the sametemperature and then allowed to cool, then 

  1. Rate of cooling is same in both

  2. Rate of cooling of A is four times that of B
  3. Rate of cooling of A is twice that of $\mathrm { B }$
  4. Rate of cooling of A is 1$/ 4$ times that of $\mathrm { B }$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Rate of cooling is proportional to Surface Area / Volume. For a sphere, SA/V = 3/r. Since diameter of A is half of B, radius of A is half of B, so SA/V for A is twice that of B.