NCERT Exemplar Class 11 Physics Solutions Chapter 11 Thermal Properties Of Matter

# NCERT Exemplar Class 11 Physics Solutions Chapter 11 Thermal Properties Of Matter

Edited By Safeer PP | Updated on Aug 08, 2022 01:05 PM IST

NCERT exemplar Class 11 Physics solutions chapter 11 discusses the topic of matter in further detail. Temperature is one of the properties that decide the state in which the matter is and how it will change as the temperature rises or falls. Students in this chapter will see how temperature and heat correlate with each other, along with how to measure temperature. The NCERT exemplar Class 11 Physics solutions chapter 11 also explains some of the major principles and laws in the thermal properties like Stefan's law, ideal gas equation, absolute temperature, and Newton's law of cooling. Go through the NCERT Class 11 Physics Solutions. The very thing that makes this chapter more practical is heat capacity, thermal expansion etc, which have major real-world applications.

## NCERT Exemplar Class 11 Physics Solutions Chapter 11: MCQ I

Question:11.1

A bimetallic strip is made of aluminium and steel . On heating, the strip will
a) remain straight
b) get twisted
c) will bend with aluminium on concave side
d) will bend with steel on concave side

The answer is the option (d) Will bend with steel on concave side.
Explanation: Initially, Aluminium and Steel are fixed together in a bimetallic strip and when you heat them, the expansion in steel will be smaller than the expansion in aluminium. Hence, the steel strip will be on the concave side, whereas the aluminium strip will be on the convex side.

Question:11.2

A uniform metallic rod rotates about its perpendicular bisector with constant angular speed. If it is heated uniformly to raise its temperature slightly
a) its speed of rotation increases
b) its speed of rotation decreases
c) its speed of rotation remains same
d) its speed increases because its moment of inertia increases

When the rod is heated uniformly to raise its temperature slightly, the length of the rod will be increased due to heating. This leads to increase in its moment of inertia (I).
Since angular momentum,L=Iω
To maintain the angular momentum conserved, ω(angular speed ) decreases with an increase in moment of inertia.

Question:11.3

The graph between two temperature scales A and B is shown in the figure. Between upper fixed point and lower fixed point there are 150 equal division on scale A and 100 on scale B. The relationship for conversion between the two scales is given by

The answer is the option
Explanation: Now, from graph tA, we know that,
Lower fixed point (LFP) =
& upper fixed point (UFP) =
Similarly, in case of scale B,
UFP =
& LFP =
Thus, the formula,

Question:11.4

An aluminium sphere is dipped into water. Which of the following is true?
a) buoyancy will be less in water at than that in water at
b) buoyancy will be more in water at than that in water at
c) buoyancy in water at will be same as that in water at
d) buoyancy may be more or less in water at depending on the radius of the sphere

We know that,
Buoyant force (B.F.) =
Where, V’ = volume of displaced liquid by dipped body
= density if liquid
Now, at 40C, the density of water is maximum, thus, the density of water and buoyant force will also be maximum at 40C.

Thus,
$\frac{F_{A}}{F_{0}}= \frac{\rho _{A}}{\rho _{0}}, where, \rho_{A}> \rho _{0}$
$\frac{F_{A}}{F_{0}}>1$or
$F_{A}>F_{0}$

Question:11.5

As the temperature is increased, the time period of a pendulum
a) increases as its effective length increases even though its centre of mass still remains at the centre of the bob
b) decreases as its effective length increases even though its centre of mass still remains at the centre of the bob
c) increases as its effective length increases due to shifting of centre of mass below the centre of the bob
d) decreases as its effective length remains same but the centre of mass shifts above the centre of the bob

The answer is the option (a) increases as its effective length increases even though its centre of mass still remains at the centre of the bob.
Explanation: Due to linear expansion, the length will increase with temperature,

Hence, the effective length and T increases on increasing temperature.

Question:11.6

Heat is associated with
a) kinetic energy of random motion of molecules
b) kinetic energy of orderly motion of molecules
c) total kinetic energy of random and orderly motion of molecules
d) kinetic energy of random motion in some cases and kinetic energy of orderly motion in other

The answer is the option (a) kinetic energy of random motion of molecules.
Explanation: Kinetic energy associated with random motion of molecules increases as vibration of molecules about their mean position increases on increasing temperature.

Question:11.7

The radius of a metal sphere at room temperature T is R, and the coefficient of linear expansion of the metal is . The sphere is heated a little by a temperature so that its new Temperature is $T+\Delta T$. The increase in the volume of the sphere is approximately

The answer is the option
Explanation: Here, we know that,
= coefficient of linear expansion
= ϒ = coefficient of cubical expansion
Now, $V_{0} = \frac{4}{3}\pi R^{3}$
$\gamma = \frac{\Delta V}{V\Delta T}$
Thus, $\Delta V=\gamma V\Delta T$
i.e.,$\Delta V=3\alpha .\frac{4}{3}\pi R ^{3}\Delta T$
$=4\pi R ^{3}\Delta T$
Hence, opt (d).

Question:11.8

A sphere, a cube, and a thin circular plate, all of the same material and same mass are initially heated to same high temperature.
a) plate will cool fastest and cube the slowest
b) sphere will cool fastest and cube the slowest
c) plate will cool fastest and sphere the slowest
d) cube will cool fastest and plate the slowest

The answer is the option (c) Plate will cool fastest and sphere the slowest.
Explanation: On cooling, loss of heat is directly proportional to surface area exposed to the surrounding, material of object & temperature difference between the surrounding and the body.
Here, opt (c) is verified as the surface area of the sphere is minimum and thus it will cool slowest, while the surface area of circular plate is maximum, and it will cool fastest.

## NCERT Exemplar Class 11 Physics Solutions Chapter 11: MCQ II

Question:11.9

Mark the correct options:
a) A system X is in thermal equilibrium with Y but not with Z. System Y and Z may be in thermal equilibrium with each other
b) A system X is in thermal equilibrium with Y but not with Z. Systems Y and Z are not in thermal equilibrium with each other
c) A system X is neither in thermal equilibrium with Y nor with Z. The systems Y and Z must be in thermal equilibrium with each other
d) A system X is neither in thermal equilibrium with Y nor with Z. The system Y and Z may be in thermal equilibrium with each other

The answer is the option (b) A system X is in thermal equilibrium with Y but not with Z. System Y and Z are not in thermal equilibrium with each other and option (d) A system X is neither in thermal equilibrium with Y nor with Z. The system Y and Z may be in thermal equilibrium with each other.
Explanation: (a) Here Y and Z are not in thermal equilibrium since,
& is not equal to .
Thus, hence, it is incorrect.
(b) System Y and Z are not in thermal equilibrium since,
and
Thus, . Thus, (b) is correct.
(c) Y and Z are not in thermal equilibrium because,
and
Thus, . Hence, opt (c) is incorrect.
(d) Here,
& $T_{x} \neq T_{z}$.
Here, may be equal to . Hence, opt (d) is correct.

Question:11.10

Gulab Jamuns’ (assumed to be spherical) are to be heated in an oven. They are available in two sizes, one twice bigger than the other. Pizzas (assumed to be discs) are also to be heated in oven. They are also in two sizes, one twice big in radius than the other. All four are put together to be heated to oven temperature. Choose the correct option from the following:
a) both size gulab jamuns will get heated in the same time
b) smaller gulab jamuns are heated before bigger ones
c) smaller pizzas are heated before bigger ones
d) bigger pizzas are heated before smaller ones

The answer is the option (b) Smaller gulab jamuns are heated before bigger ones and (c) Smaller pizzas are heated before bigger ones.
Explanation: Here, the smaller ones have a small thickness, through which heat to transfer up to depth gets heated before the bigger ones that have larger depth.
Hence, opt (b) & (c).

Question:11.11

Refer to the plot of temperature versus time showing the changes in the state of ice on heating. Which of the following is correct?

a) the region AB represents ice and water in thermal equilibrium
b) at B water starts boiling
c) at C all the water gets converted into steam
d) C to D represents water and steam in equilibrium at boiling point

The answer is the option (a) The region AB represents ice and water in thermal equilibrium and (d) C to D all represents water and steam in equilibrium at boiling point.
Explanation: If the temperature of a substance does not change on applying heat continuously, then its state changes.
Here, AB = & CD = , thus,
(i) AB, represents ice and water up to B &
(ii) CD represents water & steam.

Question:11.12

A glass full of hot milk is poured on the table. It begins to cool gradually. Which of the following is correct?
a) the rate of cooling is constant till milk attains the temperature of the surrounding
b) the temperature of milk falls off exponentially with time
c) while cooling, there is a flow of heat from milk to the surrounding as well as from surrounding to the milk but the net flow of heat is from milk to the surrounding and that is why it cools
d) all three phenomenon, conduction, convection, and radiation are responsible for the loss of heat from milk to the surroundings

The answer is the option (b) The temperature of milk falls off exponentially with time, (c) While cooling, there is a flow of heat from milk to the surrounding as well as from surrounding to the milk but the net flow of heat is from milk to the surrounding and that is why it cools and (d) All three phenomenon, conduction, convection and radiation are responsible for the loss of heat from milk to the surroundings.
Explanation:

1. Loss of heat is proportional to temperature difference with surrounding and body. As milk cools, rate of cooling decreases with time. Thus, opt (a) is incorrect.
2. The heat of milk falls exponentially by Newton’s law of cooling.
3. As compared to heat lost by milk to surrounding while cooling it, a very small amount of heat also flows from surrounding to milk. Hence, it is correct.
4. By conduction, convection, and radiation, when hot milk is spread on a table, it transfers, heat to the surroundings. Hence it is correct.

## NCERT Exemplar Class 11 Physics Solutions Chapter 11: Very Short Answer

Question:11.13

Is the bulb of a thermometer made of diathermic or adiabatic wall?
Diathermic walls are used in the bulb of thermometer as they allow to conduct heat through it into mercury of bulb, whereas adiabatic walls does not allow to pass heat through it.
A student records the initial length l, change in temperature and change in length of a rod as follows:

 S.No l (m) 1 2 10 2 1 10 3 2 20 4 3 10
If the first observation is correct, what can you say about observations 2, 3, and 4.

Here, it is given that there is a rod and a material that has linear expansion ‘’, remains same.
is same here.
Now, from observation no. 1

$\alpha=\frac{4 \times 10^{-4}}{2 \times 10}= 2 \times 10^{-5} /C^0$
Now, for observation no. 2,

viz. not equal to
Now, for observation no. 3,

viz. not equal to
Now, for the last observation, i.e., no. 4,

Question:11.14

A student records the initial length l, change in temperature and change in length of a rod as follows:

 S.No l (m) 1 2 10 2 1 10 3 2 20 4 3 10
If the first observation is correct, what can you say about observations 2, 3, and 4.

is same here.
Now, from observation no. 1

Now, for observation no. 2,

viz. not equal to
Now, for observation no. 3,

viz. not equal to
Now, for the last observation, i.e., no. 4,

Question:11.15

Why does a metal bar appear hotter than a wooden bar at the same temperature? Equivalently it also appears cooler than wooden bar if they are both colder than room temperature.

The rate of transferring heat in metal is larger than that in wood, as the conductivity of the metal bar is extremely high as compared to the wood.
Also, metal requires exceedingly small quantities of heat than wood to change temperature as the specific heat of metal is exceptionally low as compared to the wood.
Thus, due to larger conductivity and smaller specific heat metal becomes colder and hotter than wood when kept in cold and hot regions, respectively.

Question:11.16

Calculate the temperature which has same numerical value on Celsius and Fahrenheit scale.

Let us consider that the required temperature is,

Now, we know that,

Thus,
$\frac{x}{5}=\frac{x-32}{9}$
Thus,
-9x +5x = 160
-4x = 160x
Thus,
Thus,

Question:11.17

These days people use steel utensils with copper bottom. This is supposed to be good for uniform heating of food. Explain this effect using the fact that copper is the better conductor.

Copper base transfers heat quickly to food from the bottom and also needs a low quantity of heat as compared to steel because, as compared to steel, copper has higher conductivity and low specific heat. Thus, heat is supplied from burner to food in utensil quickly and in a large amount when the base is copper.

## NCERT Exemplar Class 11 Physics Solutions Chapter 11: Short Answer

Question:11.18

Find out the increase in moment of inertia I of a uniform rod about its perpendicular bisector when its temperature is slightly increased by .

Now, we know that moment of inertia (I) of a rod when its axis is along perpendicular bisector it is =

Now,
Thus,
$= \frac{1}{12} M (L ^{2}+\Delta L^{2}+2L \Delta L)^{2}$
Since is a very small term, we will neglect it,

$= \frac{ML^{2}}{12}+\frac{ML^{2}}{12}. \frac{2\Delta L}{L}$

Thus, the new moment of inertia will increase by .

Question:11.19

During summers in India, one of the common practice to keep cool is to make ice balls of crushed ice, dip it in flavoured sugar syrup and sip it. For this a stick is inserted into crushed ice and is squeezed in the palm to make it into the ball. Equivalently in winter, in those areas where it snows, people make snowballs and throw around. Explain the formation of ball out of crushed ice or snow in the light P-T diagram of water.

From the P-T graph, we know that at decreasing pressure in the liquid state at and 1 atm takes water to ice state & increasing pressure from to 1 atm takes water to ice state.
If we squeeze crushed ice, some parts of it melt into water at and fill the gap between ice flakes. Also, when we squeeze crushed ice, its melting point increases and the water present in the ice flakes freezes binding them together and making the ball more stable.

Question:11.20

100 g of water is supercooled to . At this point, due to some disturbance mechanised or otherwise some of it suddenly freezes to ice. What will be the temperature of the resultant mixture and how much mass would freeze?

Given: Mass of water = 100g
Ice mixes with water at Now, the heat required by - ice to ice $= ms\Delta t$

Thus, Q = 1000cal
Thus,

= 12.5 gm
Thus, there is 12.5 gm of water and ice in the mixture and hence its temperature remains .

Question:11.21

According to Newton’s law of cooling,
Rate of cooling(loss of heat) is proportional to Temperature difference of body & surrounding.
Thus, for option
1. Since the temperature of the surrounding and water is small, water should be kept warmer, thus, the amount of heat energy lost here is less.
2. Here a large amount of heat energy is lost since the temperature difference between water and surrounding is large.

## NCERT Exemplar Class 11 Physics Solutions Chapter 11: Long Answer

Question:11.22

We would like to prepare a scale whose length does not change with temperature. It is proposed to prepare a unit scale of this type whose length remains, say 10 cm. We can use a bimetallic strip made of brass and iron each of different length whose length would change in such a way that difference between their lengths remain constant. If and what should we take as the length of each strip?

We can use iron and brass to make the required scale. Here, one end will be connected with brass and the other end will be only of iron at a distance of 10 cm at any temperature. Let us consider the initial length of iron and brass to be-
&

Now, …… (i)
Thus,
Now, $L_{2} = L_{1} + L_{1}\alpha \Delta T$

If the rod is heated then, the length will become,

Now,

Thus, from (i),

Now, let and

3x – 2x = 10
Thus, x = 10.
Therefore, length of iron rod, (3x) = 30 & length of brass rod, (2x) = 20
Thus, the difference between the second ends will be 10 cm.

Question:11.23

We would like to make a vessel whose volume does not change with temperature. We can use brass and iron to create a volume of 100 cc. How do you think you can achieve this?

For, the above situation, we need to make a double container whose volume difference will be 100cc.
Let us consider & as the initial volumes of the iron and brass container, i.e., .
After heating by the difference will be the same, but the new volumes will be V2i &V2b.
Now,

Therefore,

$= V_{1} (1 + \gamma \Delta T)$

&

Now, let
&
Thus, 120x – 71x = 100
49x = 100

= 2.04
Thus,

Question:11.24

Calculate the stress developed inside a tooth cavity filled with copper when hot tea at temperature of is drunk. You can take body temperature to be and 1.7 x 10-5 0C, bulk modulus for copper =$140 \times 10^9 N/m^{2}.$

Let be the change in temperature,
Let be linear expansion of body,
& ϒ be the cubical expansion

Let V be the volume of the cavity and be the increase in its volume which is a result of increase in temperature by .

Now, we know that,
Thermal stress production = B x Volumetric strain

$= 140 \times 10^9 \times 5.1 \times 10^{-5} \times 20$

Thus, the stress is , viz., times of atmospheric pressure.

Question:11.25

A rail track made of steel having length 10 m is clamped on a railway line at its two ends. On a summer day due to rise in temperature by , it is deformed as shown in the figure. Find x if .

Given data:

L0 = 10m
&
Now, by using Pythagoras theorem,
$x^{2} = \left [(L + \Delta L){\frac{1}{2}} \right ]^{2} - \left (\frac{L}{2} \right )^{2}$

Thus, ……… (neglecting )

Thus,

Thus,

Thus,

Question:11.26

A thin rod having length Lo at and coefficient of linear expansion α has its two ends maintained at temperatures and , respectively. Find its new length.

From one end to another end the temperature of rod varies from to
Mean temperature of rod= $\frac{\theta _{1} + \theta _{2}}{2 ^{\circ}C}$

Here, the rate of flow of heat from A to C to B is equal
Thus,
Thus,

Here K is the coefficient of thermal conductivity.
Therefore,

Thus,
$= L_{0} \left [1 + \alpha \left (\frac{ \theta _{1} +\theta _{2}}{2} \right ) \right ]$

Question:11.27

According to Stefan’s law of radiation, a black body radiates energy from its unit surface area every second where T is the surface temperature of the black body and is known as Stefan’s constant. A nuclear weapon may be thought of as a ball of radius 0.5 m. When denoted, it reaches temperature of 106K and can be treated as a black body.
a) estimate the power it radiates
b) if surrounding has water at , how much water can 10% of the energy produced evaporate in 1 sec?
c) if all this energy U is in the form of radiation, corresponding momentum is . How much momentum per unit time does it impart on unit area at a distance of 1 km?

Given: E = per sec per sq. m
Thus, total E is equal to radiated from all surface area A per second will be power radiated by nuclear weapon
Thus, P =
Now, &

…. (R = 0.5m, T = 106K)

Thus,
…… (i)
(b) from (i)
Now, for evaporation of water 10% of this power is required.
Thus,

Now, energy required by m kg of water at to evaporate at = E required to heat up water from + E required to evaporate water into vapour

Thus,
$18 \times 10^{16 }= m [ 4180 (100-30) + 22.6 \times 10^{5}]$

(c) Now, we know that,
Momentum per unit time
$= \frac{18 \times 10^{16}}{3 \times 10^{8}}$

Thus,

Required momentum per unit time
$=\frac{6 \times 10^{8}}{4 \times 3.14 \times (10^{3})^{2}}$

## Introduction to NCERT Class 11 Exemplar Physics Solutions Chapter 11

We here provide our students with the best NCERT exemplar Class 11 Physics solutions chapter 11 PDF download that they can get for the NCERT questions. NCERT is the major part of entrance exam preparation. Therefore, being well acquainted with the NCERT questions and their solutions can give a major boost to the chapter's prep. We have here detailed NCERT exemplar Class 11 Physics chapter 11 solutions, which can be studied both online and offline by downloading the same in PDF format.

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## Topics in NCERT Exemplar Class 11 Physics Solutions Chapter 11

• 1. Introduction
• 2. Temperature and heat
• 3. Measurement of heat
• 4. Ideal gas equation and absolute temperature
• 5. Thermal expansion
• 6. Specific heat capacity
• 7. Calorimetry
• 8. Change of state
• 9. Heat transfer
• 10. Newton’s law of cooling

## What Will The Students Learn From NCERT Exemplar Class 11 Physics Solutions Chapter 11?

When your back is hurting, one can use a hot bag to heat the back muscles. The heat travels from the heat bag to the muscles and makes them relaxed. This is what thermal conductivity is. The heat or temperature can travel through one matter, only if the matter is a conductor. It depends on the matter’s physical properties, gradient, the path of heat, etc., understanding the thermal conductivity, and how it changes from one matter to another, is crucial for various real-world applications.

In this chapter and NCERT exemplar Class 11 Physics solutions chapter 11, the students will get a detailed view of how to measure temperature and heat. One will learn about heat capacity, that is how much heat is required to make the temperature change by +1 or -1 degree. Also, the learners will learn from Class 11 Physics NCERT exemplar solutions chapter 11, that when the temperature is passed through any matter, they tend to expand and increase in volume. The material that is expanding also undergoes stress, which is called thermal stress. The learner will also get an idea about Newton's law of cooling, which is; temperature change is proportional to the difference of temperature between surrounding and matter itself.

## NCERT Exemplar Class 11 Physics Solutions Chapter-Wise

 Chapter 2 Units and Measurement Chapter 3 Motion in a Straight Line Chapter 4 Motion in a Plane Chapter 5 Laws of Motion Chapter 6 Work, Energy, and Power Chapter 7 Systems of Particles and Rotational Motion Chapter 8 Gravitation Chapter 9 Mechanical Properties of Solids Chapter 10 Mechanical Properties of Fluids Chapter 12 Thermodynamics Chapter 13 Kinetic Theory Chapter 14 Oscillations Chapter 15 Waves

## NCERT Exemplar Class 11 Solutions

 NCERT Exemplar Class 11 Mathematics Solutions NCERT Exemplar Class 11 Chemistry Solutions NCERT Exemplar Class 11 Physics Solutions NCERT Exemplar Class 11 Biology Solutions

### Important Topics To Cover From NCERT Exemplar Class 11 Physics Solutions Chapter 11

· The students will learn how matters can change their physical and molecular due to heat. One will learn about the expansion of matter, insulation, the conductivity of matter, etc. in terms of heat and what factors affect these properties.

· One of the topics that are highly crucial for exam point of view is Newton's law of cooling in Class 11 Physics NCERT exemplar solutions chapter 11. From the statement of the law to the theorem and how to solve questions based on the theorem are clearly defined and discussed in the chapter.

· Lastly, students will learn about the applications of thermal expansions and thermal conductivity in both real-world scenarios and laboratory scenarios. NCERT exemplar Class 11 Physics solutions chapter 11 will help in understanding the topic in a much more practical way.

### Check Class 11 Physics Chapter-wise Solutions

 Chapter 1 Physical world Chapter 2 Units and Measurement Chapter 3 Motion in a straight line Chapter 4 Motion in a Plane Chapter 5 Laws of Motion Chapter 6 Work, Energy and Power Chapter 7 System of Particles and Rotational motion Chapter 8 Gravitation Chapter 9 Mechanical Properties of Solids Chapter 10 Mechanical Properties of Fluids Chapter 11 Thermal Properties of Matter Chapter 12 Thermodynamics Chapter 13 Kinetic Theory Chapter 14 Oscillations Chapter 15 Waves

### Frequently Asked Question (FAQs)

1. Are thermal properties crucial for JEE mains?

Yes, this chapter is one of the most crucial physics chapters as, every year, questions are asked from these topics.

2. How many questions are solved in this chapter?

We have solved all 22 questions from the main exercise that is mentioned in the NCERT exemplar class 11 physics solutions chapter 11.

3. How are these questions solved?

The questions are solved in the most detailed way for the students. We have made sure to add both theory and numerical in a way that is both CBSE accepted and is easy to retain.

4. Are these solutions helpful?

Yes, these solutions are highly helpful to clear both theoretical understandings of the chapter, and also get an idea of how to solve numerical questions in an exam.

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