NCERT Solutions for Class 11 Physics Chapter 11 Thermal Properties of Matter

NCERT Solutions for Class 11 Physics Chapter 11 Thermal Properties of Matter

Edited By Vishal kumar | Updated on Apr 29, 2025 03:32 PM IST

Did you ever think about why a metal spoon is colder than a wooden spoon even at the same temperature? Or why blacksmiths heat iron rings before placing them on wooden wheels? Thermal Properties of Matter Class 11 NCERT Solutions will provide you with answers to these questions. In this chapter, we learn about how heat moves, why the temperature sometimes does not change despite the addition of heat, and the physics involved in everyday processes such as sea breezes and boiling water. With step-by-step solutions, learning is a breeze and successful.

The NCERT solution for class 11 physics thermal properties of matter is created by experienced faculty to give precise and detailed solutions to each and every NCERT exercise problem. Students can practice important questions and learn the key concepts with the help of these thermal properties of matter NCERT solutions for class 11 prior to exams. These step-by-step solutions simplify the learning process and are free to access below.

This Story also Contains
  1. NCERT Solutions for Class 11 Physics Chapter 10 Thermal Properties of Matter: Download Solution PDF
  2. Access NCERT Solutions for Class 11 Physics Chapter 10 Thermal Properties of Matter - Exercise Solution
  3. Class 11 physics NCERT Chapter 10: Higher Order Thinking Skills (HOTS) Questions
  4. Approach to Solve Questions of Thermal Properties of Matter
  5. What Extra Should Students Study Beyond NCERT for JEE/NEET?
  6. NCERT Solutions for Class 11 Physics Chapter-Wise
  7. NCERT solutions for class 11 Subject wise

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NCERT Solutions for Class 11 Physics Chapter 10 Thermal Properties of Matter: Download Solution PDF

Free download thermal properties of matter class 11 exercise solution PDF for CBSE exam.

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Access NCERT Solutions for Class 11 Physics Chapter 10 Thermal Properties of Matter - Exercise Solution

Q. 10.1 The triple points of neon and carbon dioxide are $24.57\; K$ and $216.55\; K$ respectively. Express these temperatures on the Celsius and Fahrenheit scales.

Answer:

The relation between Kelvin and Celcius scale is T K = T C + 273.15

Triple Point of Neon in Kelvin T K = 24.57 K

Triple Point of Neon in Celcius T C = T K -273.15 = 24.57 -273.15 =-248.58 o C

Triple Point of carbon dioxide in Kelvin T K = 216.55 K

Triple Point of carbon dioxide in Celcius T C = T K -273.15 = 216.55 - 273.15 = -56.60 o C

The relation between Celcius and Fahrenheit scale is $T_{F}=\frac{9}{5}T_{C} + 32$

Triple Point of Neon in Fahrenheit is

$T_{F}=\frac{9}{5}\times (-248.58) + 32$

T F = -415.44 o C

Triple Point of carbon dioxide in Fahrenheit is

$T_{F}=\frac{9}{5}\times (-56.60) + 32$

T F = -69.88 o C

Q. 10.2 Two absolute scales $A$ and $B$ have triple points of water defined to be $200A$ and $350B$ . What is the relation between $T_{A}$ and $T_{B}$ ?

Answer:

200 A = 273 K

$T_{K}=\frac{273}{200}T_{A}$

350 B = 273 K

$T_{K}=\frac{273}{350}T_{B}$

Equating T K From the above two equations we have

$\frac{273}{200}T_{A}=\frac{273}{350}T_{B}$
$T_{A}=\frac{4}{7}T_{B}$

Q. 10.3 The electrical resistance in ohms of a certain thermometer varies with temperature according to the approximate law :

$R=R_{0}\left [ 1+\alpha (T-T_{0}) \right ]$

The resistance is $101.6\Omega$ at the triple-point of water $273.16\; K,$ and $165.5\; \Omega$ at the normal melting point of lead $(600.5\; K).$ What is the temperature when the resistance is $123.4\; \Omega$ ?

Answer:

$R=R_{0}\left [ 1+\alpha (T-T_{0}) \right ]$

R 0 = $101.6\Omega$ T 0 = $273.16 K$

R = $165.5\; \Omega$ R = $600.5 K$

Putting the above values in the given equation we have

$\\\alpha =\frac{165.5-101.6}{600.5-27316}\\ \alpha =1.92\times 10^{-2}\ K^{-1}$

For R = $123.4\; \Omega$

$\\T=T_{0}+\frac{1}{\alpha }\left ( \frac{R}{R_{0}}-1 \right )\\ $

$T=273.16+\frac{1}{1.92\times 10^{-3}}\left ( \frac{123.4}{101.6}-1 \right )\\ $

$T=384.75K$

Q. 10.4 (a) Answer the following:
(a) The triple-point of water is a standard fixed point in modern thermometry. Why ? What is wrong in taking the melting point of ice and the boiling point of water as standard fixed points (as was originally done in the Celsius scale)?

Answer:

Unlike the melting point of ice and boiling point of water, the triple point of water has a fixed value of 273.16 K. The melting point of ice and boiling point of water vary with pressure.

Q. 10.4 (c) Answer the following :

(c) The absolute temperature (Kelvin scale) $T$ is related to the temperature $t_{c}$ on the Celsius scale by

$t_{c}=T-273.15$

Why do we have $273.15$ in this relation, and not $273.16?$

Answer:

This is because 0 o C on the Celcius scale corresponding to the melting point at standard pressure is equal to 273.15 K whereas 273.16 K is the triple point of water. The triple point of water is 0.01 0 C , not 0 0 C

Q. 10.4 (d) Answer the following :

(d) What is the temperature of the triple-point of water on an absolute scale whose unit interval size is equal to that of the Fahrenheit scale?

Answer:

Let at a certain temperature the reading on Fahrenheit and Kelvin Scale be T F and T K respectively

$T_{F}-32=\frac{9}{5}(T_{K}-273)$ $(i)$

Let at another temperature the reading on Fahrenheit and Kelvin Scale be T' F and T' K respectively

$T'_{F}-32=\frac{9}{5}(T'_{K}-273)$ $(ii)$

Subtracting equation (ii) from (i)

$T_{F}-T'_{F}=\frac{9}{5}(T_{K}-T'_{K})$

For T K - T' K = 1 K, T F - T' F = 9/5

Therefore corresponding to 273.16 K the absolute scale whose unit interval size is equal to that of the Fahrenheit scale

$\\T_{F}=\frac{9}{5}\times 273.16\\ $

$T_{F}=491.688$

Q. 10.5 (a) Two ideal gas thermometers A and B use oxygen and hydrogen respectively. The following observations are made :

Temperature
Pressure
Thermometer A
Pressure
Thermometer B
Triple-point of water
Normal melting point of sulphur

(a) What is the absolute temperature of normal melting point of sulphur as read by thermometers A and B?

Answer:

$\\PV=nRT\\$

$\frac{P}{T}=\frac{nR}{V}$

As the moles of oxygen and hydrogen inside the thermometers and the volume occupied by the gases remain constant P/T would remain constant.

The triple point of water(T 1 ) = 273.16 K

Pressure in thermometer A at a temperature equal to the triple point of water (P 1 ) = $1.250\times 10^{5}Pa$

Pressure in thermometer A at a temperature equal to Normal melting point of sulphur (P 2 ) = $1.797\times 10^{5}Pa$

The normal melting point of sulphur as read by thermometer A T 2 would be given as

$T_{2}=\frac{P_{2}T_{1}}{P_{1}}$

$\\T_{2}=\frac{1.797\times 10^{5}\times 273.16}{1.250\times 10^{5}}\\ $

$T_{2}=392.69\ K$

Pressure in thermometer B at a temperature equal to the triple point of water (P1' ) = $0.200\times 10^{5}Pa$

Pressure in thermometer B at a temperature equal to Normal melting point of sulphur (P2' ) = $0.287\times 10^{5}Pa$

The normal melting point of sulphur as read by thermometer B T2' would be given as

$\\T'_{2}=\frac{P'_{2}T_{1}}{P'_{1}}\\ $

$T'_{2}=\frac{0.287\times 10^{5}\times 273.16}{0.200\times 10^{5}}\\$

$ T'_{2}=391.98\ K$

Q. 10.5 (b) Two ideal gas thermometers A and B use oxygen and hydrogen respectively. The following observations are made :

Temperature
Pressure
Thermometer A
Pressure
Thermometer B
Triple-point of water
Normal melting point of sulphur

(b) What do you think is the reason behind the slight difference in answers of thermometers A and B? (The thermometers are not faulty). What further procedure is needed in the experiment to reduce the discrepancy between the two readings?

Answer:

The slight difference in answers of thermometers A and B occur because the gases used in the thermometers are not ideal gases. To reduce this discrepancy the experiments should be carried out at low pressures where the behaviour of real gases tend close to that of ideal gases.

Q. 10.6 A steel tape 1m long is correctly calibrated for a temperature of $27.0^{\circ}C.$ The length of a steel rod measured by this tape is found to be $63.0\; cm$ on a hot day when the temperature is $45.0^{\circ}C.$ What is the actual length of the steel rod on that day? What is the length of the same steel rod on a day when the temperature is $27.0^{\circ}C\; ?$ Coefficient of linear expansion of steel $=1.20\times 10^{-5}K^{-1}.$

Answer:

At 27 o C the 63 cm (l 1 ) mark on the steel tape would be measuring exactly 63 cm as the tape is calibrated at 27 o C

Coefficient of linear expansion of steel $=1.20\times 10^{-5}K^{-1}.$

Actual length when the scale is giving a reading of 63 cm on at 45 o C is l 2

$\\l_{2}=l_{1}(1+\alpha \Delta T)\\ =63\times (1+1.20\times 10^{-5}\times (45-27))\\ =63.013608cm$

The actual length of the steel rod on a day when the temperature is 45 o C is 63.013608 cm.

Length of the same steel rod on a day when the temperature is 63 cm.

Q. 10.7 A large steel wheel is to be fitted on to a shaft of the same material. At $27^{\circ}C$ , the outer diameter of the shaft is $8.70\; cm$ and the diameter of the central hole in the wheel is $8.69\; cm$ . The shaft is cooled using ‘dry ice’. At what temperature of the shaft does the wheel slip on the shaft? Assume coefficient of linear expansion of the steel to be constant over the required temperature range : $\alpha _{steel}=1.20\times 10^{-5}K^{-1}$ .

Answer:

Diameter of the steel shaft at 27 o C (T 1 ) d 1 = 8.70 cm

The diameter of the central hole in the wheel d 2 = 8.69 cm

Coefficient of linear expansion of the steel $\alpha _{steel}=1.20\times 10^{-5}K^{-1}$ .

The wheel will slip on the shaft when the diameter of the steel shaft becomes equal to the diameter of the central hole in the wheel.

Let this happen at temperature T

$\\d_{2}=d_{1}(1+\alpha (T-T_{1}))\\ 8.69=8.7(1+1.2\times 10^{5}(T-27))\\ $

$T=-68.79\ ^{o}C$

Q. 10.8 A hole is drilled in a copper sheet. The diameter of the hole is $4.24\; cm$ at $27.0^{\circ}C.$ What is the change in the diameter of the hole when the sheet is heated to $227^{\circ}C\; ?$ Coefficient of linear expansion of copper $=1.70\times 10^{-5}K^{-1}.$

Answer:

Coefficient of linear expansion of copper $\alpha$ $=1.70\times 10^{-5}K^{-1}.$

Coefficient of superficial expansion of copper is $\beta$

$\beta =2\alpha \\ $

$\beta =2\times 1.7\times 10^{-5}\\ $

$\beta =3.4\times 10^{-5}K^{-1}$

Diameter of the hole at 27 o C (d 1 ) = 4.24 cm

Area of the hole at 227 o C is

$A_{2}=A_{1}(1+\beta \Delta T)\\ $

$A_{2}=\pi \left ( \frac{4.24}{2} \right )^{2}(1+3.4\times 10^{-5}(227-27))$
$A_{2}=14.215\ cm^{2}$

Let the diameter at 227 o C be d 2

$\\\pi \left ( \frac{d_{2}}{4} \right )^{2}=14.215\\$

$ d_{2}=4.254cm$

Change in diameter is d 2 -d 1 = 4.24 -4.254 = 0.014 cm.

Q. 10.9 A brass wire $1.8\; m$ long at $27^{\circ}C$ is held taut with little tension between two rigid supports. If the wire is cooled to a temperature of $-39^{\circ}C,$ what is the tension developed in the wire if its diameter is $2.0\; mm\; ?$ ? Co-efficient of linear $expansion\; of \; brass=2.0\times 10^{-5}K^{-1};$ $Young's\; modulus \; of\; brass=0.91\times 10^{11}Pa.$

Answer:

Youngs Modulus of Brass, $Y=0.91\times 10^{11}$

Co-efficient of linear expansion of Brass, $\alpha =2.0\times 10^{-5}K^{-1}$

The diameter of the given brass wire, d = 2.0 mm

Length of the given brass wire, l = 1.8 m

Initial Temperature T 1 = 27 o C

Final Temperature T 2 = -39 o C

$\\Y=\frac{Stress}{Strain}\\ $

$Y=\frac{\frac{F}{A}}{\frac{\Delta l}{l}}\\ $

$F=\frac{\Delta lAY}{l}\\ $

$F=\frac{(l\alpha \Delta T)AY}{l}\\ $

$F=\alpha \Delta TAY\\ $

$F=\alpha \Delta TY\pi \frac{d^{2}}{4}\\ $

$F=\frac{2.0\times 10^{-5}\times (-39-27)\times 0.91\times 10^{11}\times \pi \times (2\times 10^{-3})^{2}}{4}$

$F=-378N$

The tension developed in the wire is 378 N. The negative sign signifies this tension is inward.

Q. 10.10 A brass rod of length $50\; cm$ and diameter $3.0\; mm$ is joined to a steel rod of the same length and diameter. What is the change in length of the combined rod at $250^{\circ}C,$ if the original lengths are at $40.0^{\circ}C\; ?$ Is there a ‘thermal stress’ developed at the junction ? The ends of the rod are free to expand (Co-efficient of linear $expansion\; of\; brass=2.0\times 10^{-5}K^{-1},\; steel=1.2\times 10^{-5}K^{-1}$ ).

Answer:

Length of the rods l = 50 cm

Co-efficient of linear expansion of brass, $\\\alpha _{b}=2\times 10^{-5}K^{-1}$

Co-efficient of linear expansion of steel, $\\\alpha _{s}=1.2\times 10^{-5}K^{-1}$

Initial Temperature T 1 = 40.0 o C

Final Temperature T 2 = 250 o C

Change in length of brass rod is

$\\\Delta l_{t}=l_{t}\alpha_{b} \Delta T\\ $

$\Delta l_{t}=50\times 2.0\times 10^{-5}\times (250-40)\\ $

$\Delta l_{t}=0.21cm$

Change in length of the steel rod is

$\\\Delta l_{s}=l_{s}\alpha_{s} \Delta T\\ $

$\Delta l_{s}=50\times 1.2\times 10^{-5}\times (250-40)\\ $

$\Delta l_{s}=0.126cm$

Change in length of the combined rod is

$\\\Delta l=\Delta l_{s}+\Delta l_{b}\\ $

$\Delta l=0.126+0.21\\ $

$\Delta l=0.336cm$

Q. 10.11 The coefficient of volume expansion of glycerine is $49\times 10^{-5}K^{-1}.$ What is the fractional change in its density for a $30^{\circ}C$ rise in temperature?

Answer:

Coefficient of volume expansion of glycerine is $\gamma =49\times 10^{-5}K^{-1}$

Let initial volume and mass of a certain amount of glycerine be V and m respectively.

Initial density is

$\rho =\frac{m}{V}$

Change in volume for a 30 o C rise in temperature will be

$\\\Delta V=V(\gamma \Delta T)\\ $

$\Delta V=V(49\times 10^{-5}\times 30)\\ $

$\Delta V=0.0147V$

Final Density is

$\\\rho' =\frac{m}{V+\Delta V}\\ $

$\rho'=\frac{m}{1.0147V}\\ $

$\rho'=\frac{0.986m}{V}$

Fractional Change in density is

$\\\frac{\rho'-\rho}{\rho}\\ =\frac{\frac{0.986m}{v}-\frac{m}{v}}{\frac{m}{v}}\\ =-0.014$

The negative sign signifies with an increase in temperature density will decrease.

Q. 10.12 A $10\; kW$ drilling machine is used to drill a bore in a small aluminium block of mass $8.0\; kg.$ How much is the rise in temperature of the block in $2.5$ minutes, assuming $50^{o}/_{o}$ of power is used up in heating the machine itself or lost to the surrounding. $Spcific\; heat\; of\; aluminium=0.91\; j\; g^{-1}K^{-1}.$

Answer:

Power of the drilling machine, P = 10 kW

Time. t = 2.5 min

Total energy dissipated E is

$\\E=Pt\\$

$ E=10\times 10^{3}\times 2.5\times 60\\ $

$E=1.5\times 10^{6}J$

Thermal energy absorbed by aluminium block is

$\\\Delta Q=\frac{E}{2}\\$

$ \Delta Q=\frac{1.5\times 10^{6}}{2}\\ $

$\Delta Q=7.5\times 10^{5}J$

Mass of the aluminium block, m = 8.0 kg

Specific heat of aluminium, c = 0.91 J g -1 K -1

Let rise in temperature be $\Delta T$

$\\mc\Delta T=\Delta Q\\ $

$\Delta T=\frac{\Delta Q}{mc}\\ $

$\Delta T=\frac{7.5\times 10^{5}}{0.91\times 8\times 10^{3}}\\ $

$\Delta T=103.02\ ^{o}C$

Q. 10.13 A copper block of mass $2.5 \; kg$ is heated in a furnace to a temperature of $500^{\circ}C$ and then placed on a large ice block. What is the maximum amount of ice that can melt? (Specific heat of copper $=0.39\; j\; g^{-1}K^{-1};$ heat of fusion of water $=335\; j\; g^{-1}$ ).

Answer:

Mass of copper block m = 2.5 kg

Initial Temperature of the copper block, T 1 = 500 o C

Final Temperature of Copper block, T 2 = 0 o C

Specific heat of copper, c = 0.39 J g -1 K -1

Thermal Energy released by the copper block is $\Delta Q$

$\\\Delta Q=mc\Delta T\\ $

$\Delta Q=2.5\times 10^{3}\times 0.39\times 500\\ $

$\Delta Q=487500\ J$

Latent heat of fusion of water, L = 335 j g -1

Amount of ice that can melt is

$\\w=\frac{\Delta Q}{L}\\ $

$w=\frac{487500}{335}\\$

$ w=1455.22g$

1.455 kg of ice can melt using the heat released by the copper block.

Q. 10.14 In an experiment on the specific heat of a metal, a $0.20\; kg$ block of the metal at 150 °C is dropped in a copper calorimeter (of water equivalent $0.025\; kg$ ) containing $150\; cm^{3}$ of water at $27^{\circ}C.$ The final temperature is $40^{\circ}C.$ Compute the specific heat of the metal. If heat losses to the surroundings are not negligible, is your answer greater or smaller than the actual value for specific heat of the metal?

Answer:

Let the specific heat of the metal be C.

Mass of metal block m = 200 g

Initial Temperature of metal block = 150 o C

Final Temperature of metal block = 40 o C

The heat released by the block is

$\\\Delta Q=mc\Delta T\\ $

$\Delta Q=200\times c\times (150-40)\\ $

$\Delta Q=22000c$

Initial Temperature of the calorimeter and water = 27 o C

Final Temperature of the calorimeter and water = 40 o C

Amount of water = 150 cm

Mass of water = 150 g

Water equivalent of calorimeter = 25 g

Specific heat of water = 4.186 J g -1 K -1

Heat absorbed by the Calorimeter and water is $\\\Delta Q'$

$\\\Delta Q'=(150+25)\times 4.186\times (40-27)\\ $

$\Delta Q'=9523.15J$

The heat absorbed by the Calorimeter and water is equal to the heat released by the block

$\\\Delta Q=\Delta Q'\\ 22000c=9523.15\\ c=0.433\ J\ g^{-1}\ K^{-1}$

The above value would be lesser than the actual value since some heat must have been lost to the surroundings as well which we haven't accounted for.

Q. 10.15 Given below are observations on molar specific heats at room temperature of some common gases.

Gas Molar specific heat (Cv )

$(cal\; mol^{-1}K^{-1})$

Hydrogen 4.87

Nitrogen 4.97

Oxygen 5.02

Nitric oxide 4.99

Carbon monoxide 5.01

Chlorine 6.17

The measured molar specific heats of these gases are markedly different from those for monatomic gases. Typically, molar specific heat of a monatomic gas is $2.92\; cal/mol\; K.$ Explain this difference. What can you infer from the somewhat larger (than the rest) value for chlorine?

Answer:

Monoatomic gases have only translational degree of freedom but diatomic gases have rotational degrees of freedom as well. The temperature increases with increase in the spontaneity of motion in all degrees. Therefore, to increase the temperature of diatomic gases more energy is required than that required to increase the temperature of monoatomic gases by the same value owing to higher degrees of freedom in diatomic gases.

If we only consider rotational modes of freedom the molar specific heat of the diatomic gases would be given as

$\\c=\frac{fR}{2}\\ c=\frac{5}{2}\times 1.92\\ c=4.95\ cal\ mol^{-1}\ K^{-1}$

The number of degrees of freedom = 5 (3 translational and 2 rotational)

The values given in the table are more or less in accordance with the above calculated one. The larger deviation from the calculated value in the case of chlorine is because of the presence of vibrational motion as well.

Q. 10.16 A child running a temperature of $101^{\circ}F$ is given an antipyrin (i.e. a medicine that lowers fever) which causes an increase in the rate of evaporation of sweat from his body. If the fever is brought down to $98^{\circ}F$ in 20 minutes, what is the average rate of extra evaporation caused, by the drug. Assume the evaporation mechanism to be the only way by which heat is lost. The mass of the child is $30\; kg.$ . The specific heat of human body is approximately the same as that of water, and latent heat of evaporation of water at that temperature is about $580\; cal\; g^{-1}$ .

Answer:

Initial Temperature of the boy = 101 o F

Final Temperature of the boy = 98 o F

Change in Temperature is

$\\\Delta T=3\ ^{o}F\\ $

$\Delta T=3\times \frac{5}{9}\\ $

$\Delta T=1.67\ ^{o}C$

Mass of the child is m = 30 kg

Specific heat of human body = 1000 cal kg -1 o C -1

Heat released is $\\\Delta Q$

$\\\Delta Q=mc\Delta T\\$

$\Delta Q=30\times 1000\times 1.67\\ $

$\Delta Q=50000\ cal$

Latent heat of evaporation of water = 580 cal g -1

The amount of heat lost by the body of the boy has been absorbed by water.

Let the mass of water which has evaporated be m'

$\\\Delta Q=m'L\\ $

$ m'=\frac{Q}{L}\\ $

$m'=\frac{50000}{580}\\$

$ m'=86.2\ g$
Time in which the water has evaporated, t = 20 min.

The rate of evaporation is m'/t

$\\\frac{m'}{t}=\frac{86.2}{20}\\ $

$\frac{m'}{t}=4.31\ g\ min^{-1}$

Q. 10.17 A ‘thermacole’ icebox is a cheap and an efficient method for storing small quantities of cooked food in summer in particular. A cubical icebox of side 30 cm has a thickness of $5.0\; cm.$ If $4.0\; kg$ of ice is put in the box, estimate the amount of ice remaining after 6 h. The outside temperature is $45^{\circ}C.$ and co-efficient of thermal conductivity of thermacole is $0.01\; j\; s^{-1}m^{-1}K^{-1}.$ $[Heat\; of\; fusion\; of\; water=335\times 103\; j\; kg^{-1}]$

Answer:

Side of the box s = 30 cm

Area available for conduction A

A = 6s 2

A=6(30) 2

A=5400 cm 2 = 0.54 m 2

Temperature difference = 45 o C

Co-efficient of thermal conductivity of thermacole is k = 0.01 J s -1 m -1 K -1

Width of the box is d = 5 cm

Heat absorbed by the box in 6 hours is $\Delta Q$

$\\\Delta Q=\frac{kA\Delta T}{l}\\ $

$\Delta Q=\frac{0.01\times 0.54\times 45\times 6\times 60\times 60}{0.05}\\ $

$\Delta Q=104976\ J$

The heat of fusion of water is $L=335\times 10^{3}\ J\ kg^{-1}$

The amount of ice which has melted is m'

$\\m'=\frac{\Delta Q}{L}\\ $

$m'=\frac{104976}{335\times 10^{3}}\\ $

$m'=0.313\ kg$

Amount of ice left after 6 hours = 4 - 0.313 = 3.687 kg

Q. 10.18 A brass boiler has a base area of $0.15\; m^{2}$ and thickness $1.0\; cm.$ It boils water at the rate of $6.0 \; kg/min$ when placed on a gas stove. Estimate the temperature of the part of the flame in contact with the boiler. Thermal conductivity of brass $=109\; j\; s^{-1}m^{-1}K^{-1};$ Heat of vaporisation of water $=2256\times 103\; j\; kg^{-1}.$

Answer:

The rate at which water boils, R = 6.0 kg min -1

The heat of vaporisation of water, $L=2256\times 10^{3}\ J\ kg^{-1}$

The rate at which heat enters the boiler

$\\\frac{dQ}{dT}=RL\\ $

$\frac{dQ}{dT}=\frac{6\times 2256\times 10^{3}}{60}\\ $

$\frac{dQ}{dT}=2.256\times 10^{5}Js^{-1}$

The base area of the boiler, A = 0.15 m 2

Thickness, l = 1.0 cm

Thermal conductivity of brass $=109\; j\; s^{-1}m^{-1}K^{-1};$

The temperature inside the boiler = Boiling point of water = 100 o C

Let the temperature of the flame in contact with the boiler be T

The amount of heat flowing into the boiler is

$\\\frac{dQ}{dt}=\frac{KA\Delta T}{l}\\ 2.256\times 10^{5}=\frac{109\times 0.15\times (T-100)}{1\times 10^{-2}}\\ T-100=137.98\\ T=237.98\ ^{o}C$

The temperature of the flame in contact with the boiler is 237.98 o C

Q. 10.19 (a) Explain why :

(a) a body with large reflectivity is a poor emitter

Answer:

A body with a large reflectivity is a poor absorber. As we know a body which is a poor absorber will as well be a poor emitter. Therefore, a body with large reflectivity is a poor emitter.

Q .10.19 (b) Explain why :

(b) a brass tumbler feels much colder than a wooden tray on a chilly day

Answer:

Brass is a good conductor of heat. Therefore once someone touches brass heat from their body flows into it and it feels cold, in case of a wooden tray, no such conduction of heat from the body takes place as wood is a very poor conductor of heat.

Q. 10.19 (c) Explain why :

(c) an optical pyrometer (for measuring high temperatures) calibrated for an ideal black body radiation gives too low a value for the temperature of a red hot iron piece in the open but gives a correct value for the temperature when the same piece is in the furnace

Answer:

An optical pyrometer relates the brightness of a glowing body with its temperature. In the open because of other sources of light the sensor in the optical pyrometer does not detect the true brightness of a red hot piece of iron and thus does not predict its temperature correctly whereas in the furnace the piece of iron is the only source of light and the sensor detects its brightness correctly thus giving the correct value of the temperature.

Q. 10.19 (d) Explain why :

(d) the earth without its atmosphere would be inhospitably cold

Answer:

The sun rays contain infrared radiations. These are reflected back by the lower part of the atmosphere after being reflected by the surface of the earth and are trapped inside the atmosphere thus maintaining the Earth's temperature at a hospitable level. Without these rays being trapped the temperature of the earth will go down severely and thus the Earth without its atmosphere would be inhospitably cold.

Q. 10.19 (e) Explain why :

(e) heating systems based on circulation of steam are more efficient in warming a building than those based on circulation of hot water

Answer:

Heating systems based on the circulation of steam are more efficient in warming a building than those based on the circulation of hot water because the same amount of steam at 100 o C contains more energy available for heat dissipation than the same amount of water at 100 o C in the form of latent heat of vaporization.

Q. 10.20 A body cools from $80^{\circ}C$ to $50^{\circ}C$ in 5 minutes. Calculate the time it takes to cool from $60^{\circ}C$ to $30^{\circ}C.$ The temperature of the surroundings is $20^{\circ}C.$

Answer:

Let a body initially be at temperature T 1

Let its final Temperature be T 2

Let the surrounding temperature be T 0

Let the temperature change in time t.

According to Newton's Law of cooling

$\\-\frac{dT}{dt}=K(T-T_{0})\\ $

$\frac{dT}{T-T_{0}}=-Kdt\\$

$ \int_{T_{1}}^{T_{2}}\frac{dT}{T-T_{0}}=-K\int_{0}^{t}dt\\$
$ \left [ ln(T-T_{0}) \right ]_{T_{1}}^{T_{2}}=-K[t]_{0}^{t}\\ $
$ln\left ( \frac{T_{2}-T_{0}}{T_{1}-T_{0}} \right )=-Kt$

where K is a constant.

We have been given that the body cools from 80 o C to 50 o C in 5 minutes when the surrounding temperature is 20 o C.

T 2 = 50 o C

T 1 = 80 o C

T 0 = 20 o C

t = 5 min = 300 s.

$\\ln\left ( \frac{50-20}{80-20} \right )=-K\times 300\\ K=\frac{ln(2)}{300}\\$

For T 1 = 60 o C and T 2 = 30 o C we have

$\\ln\left ( \frac{30-20}{60-20} \right )=-\frac{ln2}{300}t\\ $
$t=\frac{ln(4)\times 300}{ln(2)} \\$
$t=\frac{2ln(2)\times 300}{ln(2)}\\ $
$t=600\ s\\ $
$t= 10\ min$

The body will take 10 minutes to cool from 60 o C to 30 o C at the surrounding temperature of 20 o C.

Class 11 physics NCERT Chapter 10: Higher Order Thinking Skills (HOTS) Questions

Q1:

When 100 g of liquid A at 100oC is added to 50 g of liquid B at a temperature of 75oC, the temperature of the mixture becomes 90oC. The temperature of the mixture (in oC), if 100 g of liquid A at 100oC is added to 50 g of liquid B at 50oC, will be :

Answer:

Specific Heat -

$
\begin{aligned}
& C=\frac{Q}{m \cdot \Delta \theta} \\
& \text { - wherein } \\
& \mathrm{C}=\text { specific heat } \\
& \Delta \theta=\text { Change in temperature } \\
& \mathrm{m}=\text { Amount of mass } \\
& \text { For (I) } \\
& 100 \times S_A \times(100-90)=50 \times S_B \times(90-75) \\
& S_A=\frac{1.5}{2} S_B=\frac{3}{4} S_B \cdots(1) \\
& \text { now for }(\mathrm{II}) \\
& 100 \times S_A \times(100-T)=50 \times S_B \times(T-50) \\
& \Rightarrow 2 S_A(100-T)=S_B(T-50) \cdots(2)
\end{aligned}
$
From (1) & (2)

$
\begin{aligned}
& 2 \times \frac{3}{4} \times(100-T)=(T-50) \\
& 3(100-T)=2(T-50) \\
& 300-3 T=2 T-100 \\
& 400=5 T \\
& T=80^{\circ} \mathrm{C}
\end{aligned}
$


Q2:

If the length of cylinder on heating increases by 2% then the area of base of cylinder will increase by

Answer: Assuming the initial length of the cylinder is $\ell_1$, the linear expansion coefficient is $\alpha$, and the temperature rise is $\Delta t^{\circ} \mathrm{C}$, $$ \begin{aligned} & \Delta \ell=\ell \alpha \Delta t \Rightarrow \frac{\Delta \ell}{\ell} \times 100=\alpha \Delta t \times 100 \\ & \therefore 2=\alpha \Delta t \times 100 \end{aligned} $$ Now, for area $$ \begin{aligned} & \Delta \mathrm{A}=\mathrm{A} \beta \Delta \mathrm{t} \Rightarrow \frac{\Delta \mathrm{~A}}{\mathrm{~A}}=\beta \Delta \mathrm{t} \\ & \Rightarrow \frac{\Delta \mathrm{~A}}{\mathrm{~A}} \times 100=\beta \Delta \mathrm{t} \times 100 \\ & \% \text { change in area }=\beta \Delta \mathrm{t} \times 100 \\ & =\beta \Delta \mathrm{t} \times 100 \end{aligned} $$ We know that $2 \times \alpha \times \Delta t=\beta \times \Delta t$ $$ \begin{aligned} & =2 \alpha \Delta t \times 100 \\ & =2(\alpha \Delta t \times 100) \\ & =2 \times 2 \\ & =4 \% \end{aligned} $$


Q3: A cylindrical metal rod of length L0 is shaped into a ring with a small gap as shown in Figure. On heating the system,

A. x will decrease, R will increase

B. Both x and R will decrease

C. Both x and R will increase

D. R will increase, x will remain same

Answer:

Linear Expansion - When a solid is heated and its length increases, then the Expansion is called linear Expansion.
On the heating, the system x and R both will increase since the expansion of isotropic solids is similar to true photographic enlargement.


Q4:

The coefficient of thermal expansion of a rod varies with temperature as $\alpha=\alpha_0+\alpha_0 \frac{T}{T_0}$ where T is the temperature of the body and all others are positive constants. If the temperature of the rod of length $\ell_0$ is changed from $T_0 / 2$ to $T_0$ uniformly with time, then what is the ratio of rate of fractional change of length initially and finally?

Answer:

We know coefficient of thermal expansion is given as

$
\begin{gathered}
\quad \frac{\mathrm{d} L}{L \mathrm{~d} T}=\alpha \\
\Rightarrow \frac{\mathrm{d} L}{L \mathrm{dt}}=\alpha \frac{\mathrm{d} T}{\mathrm{~d} t} \\
\frac{\left(\frac{d L}{L d t}\right)_1}{\left(\frac{d L}{L d t}\right)_2}=\frac{\alpha_1 \frac{d T}{d t}}{\alpha_2 \frac{d T}{d t}} \\
\Rightarrow \\
\frac{\left(\frac{d L}{L d}\right)_1}{\left(\frac{d L}{L d t}\right)_2}=\frac{\alpha_1}{\alpha_2} \\
\Rightarrow
\frac{\alpha_0+\alpha_0 \frac{T_0 / 2}{T_0}}{\alpha_0+\alpha_0 \frac{T_0}{T_0}}=\frac{3 / 2}{2}=\frac{3}{4}
\end{gathered}
$


Q5:

A red hot iron (mass 25 g) has a temperature of 100ºC. It is immersed in a mixture of ice and water at thermal equilibrium. The volume of the mixture is found to be reduced by $0.15 \mathrm{~cm}^3$with the temperature of the mixture remains constant. Find the specific heat (in cal gm ${ }^0 \mathrm{C}$) of the metal.

Given specific gravity of ice = 0.92, specific gravity of water at $0^{\circ} \mathrm{C}=1.0$, latent heat of fusion of ice $=80 \mathrm{calg}^{-1}$.

Answer:

As the ice melts its density changes which causes change in volume. Let m g of ice melt.

$\begin{aligned} & \frac{m}{\rho_{i c e}}-\frac{m}{\rho_{\mathrm{H}_2 \mathrm{O}}}=0.15 \\ & m=\frac{0.15 \times 0.92}{0.08} \\ & \therefore \quad H_{\text {lost }}=H_{\text {gaired }} \\ & \Rightarrow \quad 25 \times S \times 100=\frac{0.15 \times 0.92}{0.08} \times 80 \\ & S=0.06 \mathrm{cal} \mathrm{gm}^{\circ} \mathrm{C}\end{aligned}$


Approach to Solve Questions of Thermal Properties of Matter

  • Understand heat and temperature:-
  1. Temperature: Measure of hotness
  2. Heat: Energy transferred due to temperature difference
  3. Units: Heat (Q) in joules (J), Temperature in °C/K
  • Use formula for specific heat capacity:- \begin{aligned}
    &Q=m c \Delta T\\
    &\text { Where } Q=\text { heat, } m=\text { mass, } c=\text { specific heat, } \Delta T=\text { change in temperature }
    \end{aligned}
  • Know about heat transfer methods:- Conduction, convection, and radiation – learn the simple difference
  • Apply Newton's Law of Cooling:-
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\begin{aligned}
&\frac{d T}{d t}=-k\left(T-T_{\text {env }}\right)\\
&\text { Used for cooling rate problems }
\end{aligned}

  • Learn phase change (latent heat):-
  1. At melting/boiling, temperature is constant
  2. Q = mL (L = latent fusion/vaporization heat)
  • Apply thermal expansion equations:-
  1. Linear expansion: $\Delta L=L \alpha \Delta T$
  2. Areal expansion: $\Delta A=A \beta \Delta T$
  3. Volumetric expansion: $\Delta V=V \gamma \Delta T$
  • Understand calorimetry (principle of heat exchange):-
  1. Heat lost = Heat gained
  2. Set up equations based on heat transfer and solve
  • Apply Stefan-Boltzmann Law (for radiation):-
  1. $
    P=\sigma A T^4
    $

  2. Power radiated by a body depends on its temperature

  • Be consistent with units:- Temperature in Kelvin, mass in kg, heat in Joules

  • Practice diagrams & graphs:-

  1. Cooling curves, temperature vs time, phase change graphs

  2. Visuals serve to address theory and concept-type questions


What Extra Should Students Study Beyond NCERT for JEE/NEET?

NCERT Solutions for Class 11 Physics Chapter-Wise

NCERT solutions for class 11 Subject wise

Also Check NCERT Books and NCERT Syllabus here

Subject wise NCERT Exemplar solutions

Frequently Asked Questions (FAQs)

1. How important is the chapter Thermal Properties of Matter for NEET

One question can be expected for NEET exam from the chapter Thermal Properties of Matter. Students can practice more questions from previous year NEET papers.

2. How important is Thermal Properties of Matter Class 11 for JEE Main

One question may be asked from Class 11 Physics chapter 10 Thermal Properties of Matter  for JEE Main exam. This is one important chapter for KVPY and NSEP exms. Students can get more problems on the chapter from the NCERT Exemplar.

3. What are the important topics of the chapter Thermal Properties of Matter

Topics covered in NCERT book Class 11 chapter Thermal Properties of Matter are-

  • Temperature and heat   
  • Measurement of temperature   
  • Ideal-gas equation and absolute temperature   
  • Thermal expansion   
  • Specific heat capacity   
  • Calorimetry   
  • Change of state   
  • Heat transfer   
  • Newton’s law of cooling   

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Upcoming School Exams

Application Date:16 May,2025 - 25 May,2025

Application Date:16 May,2025 - 25 May,2025

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A block of mass 0.50 kg is moving with a speed of 2.00 ms-1 on a smooth surface. It strikes another mass of 1.00 kg and then they move together as a single body. The energy loss during the collision is

Option 1)

0.34\; J

Option 2)

0.16\; J

Option 3)

1.00\; J

Option 4)

0.67\; J

A person trying to lose weight by burning fat lifts a mass of 10 kg upto a height of 1 m 1000 times.  Assume that the potential energy lost each time he lowers the mass is dissipated.  How much fat will he use up considering the work done only when the weight is lifted up ?  Fat supplies 3.8×107 J of energy per kg which is converted to mechanical energy with a 20% efficiency rate.  Take g = 9.8 ms−2 :

Option 1)

2.45×10−3 kg

Option 2)

 6.45×10−3 kg

Option 3)

 9.89×10−3 kg

Option 4)

12.89×10−3 kg

 

An athlete in the olympic games covers a distance of 100 m in 10 s. His kinetic energy can be estimated to be in the range

Option 1)

2,000 \; J - 5,000\; J

Option 2)

200 \, \, J - 500 \, \, J

Option 3)

2\times 10^{5}J-3\times 10^{5}J

Option 4)

20,000 \, \, J - 50,000 \, \, J

A particle is projected at 600   to the horizontal with a kinetic energy K. The kinetic energy at the highest point

Option 1)

K/2\,

Option 2)

\; K\;

Option 3)

zero\;

Option 4)

K/4

In the reaction,

2Al_{(s)}+6HCL_{(aq)}\rightarrow 2Al^{3+}\, _{(aq)}+6Cl^{-}\, _{(aq)}+3H_{2(g)}

Option 1)

11.2\, L\, H_{2(g)}  at STP  is produced for every mole HCL_{(aq)}  consumed

Option 2)

6L\, HCl_{(aq)}  is consumed for ever 3L\, H_{2(g)}      produced

Option 3)

33.6 L\, H_{2(g)} is produced regardless of temperature and pressure for every mole Al that reacts

Option 4)

67.2\, L\, H_{2(g)} at STP is produced for every mole Al that reacts .

How many moles of magnesium phosphate, Mg_{3}(PO_{4})_{2} will contain 0.25 mole of oxygen atoms?

Option 1)

0.02

Option 2)

3.125 × 10-2

Option 3)

1.25 × 10-2

Option 4)

2.5 × 10-2

If we consider that 1/6, in place of 1/12, mass of carbon atom is taken to be the relative atomic mass unit, the mass of one mole of a substance will

Option 1)

decrease twice

Option 2)

increase two fold

Option 3)

remain unchanged

Option 4)

be a function of the molecular mass of the substance.

With increase of temperature, which of these changes?

Option 1)

Molality

Option 2)

Weight fraction of solute

Option 3)

Fraction of solute present in water

Option 4)

Mole fraction.

Number of atoms in 558.5 gram Fe (at. wt.of Fe = 55.85 g mol-1) is

Option 1)

twice that in 60 g carbon

Option 2)

6.023 × 1022

Option 3)

half that in 8 g He

Option 4)

558.5 × 6.023 × 1023

A pulley of radius 2 m is rotated about its axis by a force F = (20t - 5t2) newton (where t is measured in seconds) applied tangentially. If the moment of inertia of the pulley about its axis of rotation is 10 kg m2 , the number of rotations made by the pulley before its direction of motion if reversed, is

Option 1)

less than 3

Option 2)

more than 3 but less than 6

Option 3)

more than 6 but less than 9

Option 4)

more than 9

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