Additional Questions - Chapter 8 Heat and Thermodynamics 11th Science Guide Samacheer Kalvi Solutions - SaraNextGen [2024-2025]

Updated On May 15, 2024

By SaraNextGen

Additional Questions Solved
I. Choose the correct answer from the following:
Question 1.
The coefficient of volume expansion of a solid is $\mathrm{x}$ times the coefficient of superficial expansion. Then $\mathrm{x}$ is
(a) 1.5
(b) 2
(c) 2.5
(d) 3
Answer:
(a) 1.5
Solution: $\alpha=\frac{\beta}{2}=\frac{\gamma}{3} \quad \gamma=x \beta$
$
\begin{aligned}
\therefore \quad \gamma & =\frac{3}{2} \beta \Rightarrow \gamma=1.5 \beta \\
x & =1.5
\end{aligned}
$
Question 2.
A solid metal ball has a spherical cavity. If the ball is heated, the volume of the cavity will

(a) increase
(b) decrease
(c) remain unaffected
(d) remain unaffected but the shape of the cavity will change.
Answer:
(a) increase
Question 3.
A metal sheet with a circular hole is heated. The hole will
(a) contract
(b) expand
(c) remain unaffected
(d) contract or expand depending on the value of the linear expansion coefficient.
Answer:
(b) expand
Question 4.
The length of a metal rod at $0^{\circ} \mathrm{C}$ is $0.5 \mathrm{~m}$. When it is heated, its length increases by $2.7 \mathrm{~mm}$. The final temperature of the rod is (coefficient of linear expansion of the metal $=90 \times 10^6 /{ }^{\circ} \mathrm{C}$ ) $\ldots \ldots$
(a) $20^{\circ} \mathrm{C}$
(b) $30^{\circ} \mathrm{C}$
(c) $40^{\circ} \mathrm{C}$
(d) $60^{\circ} \mathrm{C}$
Answer:
(d) $60^{\circ} \mathrm{C}$
$1_t=1_0(1+\alpha \mathrm{t})$
$\quad l_{\mathrm{t}}=l_0(1+\alpha t)$

$
\therefore \quad \quad t=\frac{l_t-l_0}{l_0 \alpha}=\frac{2.7 \times 10^{-3}}{0.5 \times 90 \times 10^{-6}} \quad ; t=60^{\circ}
$
Question 5.
A bimetal made of copper and iron strips welded together is straight at room temperature. It is held vertically with iron strip towards left and copper strip towards right. If this bimetal is heated, it will
(a) remain straight
(b) bend towards right
(c) bend towards left
(d) bend forward
Answer:
(c) bend towards left
Solution:
Since $\alpha_{\text {copper }}>\alpha_{\text {iron }}$, the bimetal will bend towards iron, i.e., towards left.
Question 6.
When water is heated from $0^{\circ} \mathrm{C}$ to $10^{\circ} \mathrm{C}$, its volume

(a) decreases
(b) increases
(c) first increase and then decrease
(d) first decreases and then increases.
Answer:
(d) first decreases and then increases.
Question 7.
A block of wood is floating on water at $0^{\circ} \mathrm{C}$ with a certain volume $\mathrm{V}$ above water level. The temperature of water is slowly raised to $20^{\circ} \mathrm{C}$. How does the volume $\mathrm{V}$ change with the rise of temperature?
(a) remain unchanged
(b) decrease continuously
(c) decrease till $4^{\circ} \mathrm{C}$ and then increase
(d) increase till $4^{\circ} \mathrm{C}$ and then decrease.
Answer:
(a) increase till $4^{\circ} \mathrm{C}$ and then decrease.
Solution:
The density of water increases from $0^{\circ}$ to $4^{\circ} \mathrm{C}$ and then decreases. Therefore, the volume $\mathrm{V}$ of the block above water level will increase till $4^{\circ} \mathrm{C}$ and then decrease.
Question 8.
An iron tyre is to be fitted on a wooden wheel $0.1 \mathrm{~m}$ in diameter. The diameter of the tyre is $6 \mathrm{~mm}$ smaller than that of the wheel. The tyre should be heated by a temperature of (coefficient of volume expansion of iron is $3.6 \times 10^{-5} /{ }^{\circ} \mathrm{C}$ )
(a) $167^{\circ} \mathrm{C}$
(b) $334^{\circ} \mathrm{C}$
(c) $500^{\circ} \mathrm{C}$
(d) $1000^{\circ} \mathrm{C}$
Answer:
(a) $167^{\circ} \mathrm{C}$

Solution:
$
\begin{aligned}
\Delta l & =l \alpha \Delta t \\
0.006 & =0.994 \times 3.6 \times 10^{-5} \times \Delta t \\
\Delta t & =\frac{0.006}{0.994 \times 3.6 \times 10^{-5}}=167^{\circ} \mathrm{C}
\end{aligned}
$
Question 9.
A steel rod of length $25 \mathrm{~cm}$ has a cross-sectional area of $0.8 \mathrm{~cm}^2$. The force required to stretch this rod by the same amount as the expansion produced by heating it through $10^{\circ} \mathrm{C}$ is (coefficient of linear expansion of steel is $1051^{\circ} \mathrm{C}$ and Young's modulus of steel is $\left.2 \times 10^{10} \mathrm{~N} / \mathrm{m}^2\right) \ldots \ldots$.
(a) $40 \mathrm{~N}$
(b) $80 \mathrm{~N}$
(c) $120 \mathrm{~N}$
(d) $160 \mathrm{~N}$
Answer:
(d) $160 \mathrm{~N}$
Solution:
The required force is given by

$
\begin{aligned}
& \mathrm{F}=\mathrm{YA} \alpha \Delta t=2 \times 10^{10} \times 0.8 \times 10^{-4} \times 10^{-5} \times 10 \\
& \mathrm{~F}=160 \mathrm{~N}
\end{aligned}
$
Question 10.
Which of the following will make the volume of an ideal gas four times?
(a) double the absolute temperature and double the pressure.
(b) Halve the absolute temperature and double the pressure.
(c) Quarter the absolute temperature at constant pressure.
(d) Quarter the pressure at constant temperature.
Answer:
(d) Quarter the pressure at constant temperature.
Question 11.
A perfect gas at $27^{\circ} \mathrm{C}$ is heated at constant pressure so as to double its volume. The temperature of the gas becomes.
(a) $54^{\circ} \mathrm{C}$
(b) $150 \mathrm{~K}$
(c) $327^{\circ} \mathrm{C}$
(d) $327 \mathrm{~K}$
Answer:
(c) $327^{\circ} \mathrm{C}$
Solution:
$
\frac{\mathrm{V}^{\prime}}{\mathrm{T}^{\prime}}=\frac{\mathrm{V}}{\mathrm{T}} \Rightarrow \mathrm{T}^{\prime}=\left(\frac{\mathrm{V}^{\prime}}{\mathrm{V}}\right) \mathrm{T}=\left(\frac{2 \mathrm{~V}}{\mathrm{~V}}\right)(273+27)=600 \mathrm{~K} \Rightarrow \mathrm{T}^{\prime}=327^{\circ} \mathrm{C}
$
Question 12.
An air bubble doubles in radius on rising from the bottom of a lake to its surface. If the atmospheric pressure is equal to that of a column of water of height $\mathrm{H}$, the depth of lake is
(a) $\mathrm{H}$

(b) $2 \mathrm{H}$
(c) $7 \mathrm{H}$
(d) $8 \mathrm{H}$
Answer:
(c) $7 \mathrm{H}$
Solution:
Since the radius becomes double, the volume becomes eight times. Therefore, according to Boyle's law, the pressure becomes one-eighth. Now, the pressure at the surface Hpg. Therefore pressure at the bottom must be $8 \mathrm{H} g$. Hence the depth of the lake is $7 \mathrm{H}$.
Question 13.
The mass of 1 litre of helium under a pressure of $2 \mathrm{~atm}$ and at a temperature of $27^{\circ} \mathrm{C}$ is
(a) $0.16 \mathrm{~g}$
(b) $0.32 \mathrm{~g}$
(c) $0.48 \mathrm{~g}$
(d) $0.64 \mathrm{~g}$
Answer:
(b) $0.32 \mathrm{~g}$
Solution: No. of moles $(n)=\frac{\mathrm{PV}}{\mathrm{RT}}=\frac{2 \times 10^5 \times 10^{-3}}{8.3 \times 300}=0.08$

Mass of one mole of $\mathrm{He}=4 \mathrm{~g}$
$
\text { Mass of } n \text { moles }=(n \times 4)=(0.08 \times 4)=0.32 \mathrm{~g}
$
Question 14.
Pressure exerted by a perfect gas is equal to
(a) mean kinetic energy per unit volume
(b) half of mean kinetic energy per unit volume
(c) one-third of mean kinetic energy per unit volume
(d) two-thirds of mean kinetic energy per unit volume
Answer:
(d) two-thirds of mean kinetic energy per unit volume
Solution: $P=\frac{2}{3}$ K.E.
Question 15.
Two vessels A and $B$ contain the same ideal gas. The volume of $B$ is twice that of $A$, the pressure in $\mathrm{B}$ is twice that in $\mathrm{A}$ and the temperature of $\mathrm{B}$ is twice that of $\mathrm{A}$. The ratio of the number of gas molecules in $\mathrm{A}$ and $\mathrm{B}$ is
(a) $1: 2$
(b) $2: 1$
(c) $1: 4$
(d) $4: 1$
Answer:
(a) $1: 2$
Solution: Number of moles in $\mathrm{A}$ is, $n_{\mathrm{A}}=\frac{\mathrm{PV}}{\mathrm{RT}}$
Number of moles in $\mathrm{B}$ is, $\quad n_{\mathrm{B}}=\frac{(2 \mathrm{P})(2 \mathrm{~V})}{\mathrm{R}(2 \mathrm{~T})}=2 n_{\mathrm{A}}$

$
n_{\mathrm{A}}: n_{\mathrm{B}}=1: 2
$
Question 16.
According to Boyle's law, $\mathrm{PV}=\mathrm{C}$ when the temperature of the gas remains constant. The value of $\mathrm{C}$ depends on
(a) temperature of the gas
(b) nature of the gas
(c) quantity of the gas
(d) both temperature and quantity of the gas.
Answer:
(d) both temperature and quantity of the gas.
Question 17.
The pressure of a gas contained in a closed vessel is increased by $0.4 \%$ when heated by $1^{\circ} \mathrm{C}$. The initial temperature was
(a) $250 \mathrm{~K}$
(b) $250^{\circ} \mathrm{C}$
(c) $25 \mathrm{~K}$
(d) $25^{\circ} \mathrm{C}$

Answer:
(c) $25 \mathrm{~K}$
Solution:
$
\begin{aligned}
\frac{\mathrm{P}}{\mathrm{T}} & =\text { constant } \\
\frac{\Delta \mathrm{P}}{\mathrm{P}}-\frac{\Delta \mathrm{T}}{\mathrm{T}} & =0 \\
\mathrm{~T} & =\left(\frac{\mathrm{P}}{\Delta \mathrm{P}}\right) \Delta \mathrm{T}=\frac{100}{0.4} \times 1 ; \mathrm{T}=250 \mathrm{~K}
\end{aligned}
$
Question 18 .
A temperature difference of $25^{\circ} \mathrm{C}$ is equivalent to a temperature difference of
(a) $25^{\circ} \mathrm{F}$
(b) $45^{\circ} \mathrm{F}$
(c) $67^{\circ} \mathrm{F}$
(d) $77^{\circ} \mathrm{F}$
Answer:
(b) $45^{\circ} \mathrm{F}$
Solution: $\frac{\mathrm{F}-32}{9}=\frac{C}{5} \Rightarrow F_2-F_1=\frac{9}{5}\left(C_2-C_1\right)=\frac{9}{5} \times 25=45^{\circ} \mathrm{F}$
Question 19.
A temperature at which both the Fahrenheit and the centigrade scales have the same value is
(a) $40^{\circ}$
(b) $-40^{\circ}$
(c) 20
(d) $-20^{\circ}$
Answer:
(b) $-40^{\circ}$

Solution: Let the required temperature be $t$. then, $\frac{t}{5}=\frac{t-32}{9} \Rightarrow t=-40^{\circ}$
Question 20.
If the temperature of patient is $40^{\circ} \mathrm{C}$, his temperature on the Fahrenheit scale will be
(a) $72^{\circ} \mathrm{F}$
(b) $96^{\circ} \mathrm{F}$
(c) $100^{\circ} \mathrm{F}$
(d) $104^{\circ} \mathrm{F}$
Answer:
(d) $104^{\circ} \mathrm{F}$
Solution: $\frac{\mathrm{F}-32}{9}=\frac{40}{5} \Rightarrow \mathrm{F}=104^{\circ} \mathrm{F}$

Question 21.
The correct value of $0^{\circ} \mathrm{C}$ on the Kelvin scale is
(a) $273.15 \mathrm{~K}$
(b) $272.85 \mathrm{~K}$
(c) $273 \mathrm{~K}$
(d) $273.2 \mathrm{~K}$
Answer:
(a) $273.15 \mathrm{~K}$
Question 22.
When a gas in a closed vessel was heated so as to increase its temperature by $5^{\circ} \mathrm{C}$, there occurred an increase of $1 \%$ in its pressure, the original temperature of the gas was .......
(a) $50^{\circ} \mathrm{C}$
(b) $227^{\circ} \mathrm{C}$
(c) $273^{\circ} \mathrm{C}$
(d) $500^{\circ} \mathrm{C}$
Answer:
(b) $227^{\circ} \mathrm{C}$
Solution: $\frac{\mathrm{P}}{\mathrm{T}}=\frac{1.01 \mathrm{P}}{\mathrm{T}+5} \Rightarrow \mathrm{T}=500 \mathrm{~K}=227^{\circ} \mathrm{C}$
Question 23.
A perfect gas at $27^{\circ} \mathrm{C}$ is heated at constant pressure so as to double its volume. The temperature of the gas will be ......
(a) $600^{\circ} \mathrm{C}$
(b) $54^{\circ} \mathrm{C}$
(c) $327^{\circ} \mathrm{C}$
(d) $300^{\circ} \mathrm{C}$
Answer:
(c) $327^{\circ} \mathrm{C}$

Solution: $\frac{\mathrm{V}}{\mathrm{T}}=$ constant $\Rightarrow \frac{2 \mathrm{~V}}{\mathrm{~T}^{\prime}}=\frac{\mathrm{V}}{273+27} \Rightarrow \mathrm{T}^{\prime}=600 \mathrm{~K}=327^{\circ} \mathrm{C}$
Question 24.
Temperature can be expressed as a derived quantity in terms of
(a) length and mass
(b) mass and time
(c) length, mass and time
(d) none of these
Answer:
(d) none of these
Question 25.
The equation of state corresponding to $8 \mathrm{~g}$ of $\mathrm{O}_2$ is
(a) $\mathrm{PV}=8 \mathrm{RT}$
(b) $\mathrm{PV}=\mathrm{RT} / 4$
(c) $\mathrm{PV}=\mathrm{RT}$
(d) $\mathrm{PV}=\mathrm{RT} / 2$
Answer:
(b) $\mathrm{PV}=\mathrm{RT} / 4$

$8 \mathrm{~g}$ of $\mathrm{O}_2$ is $1 / 4$ of a mole of $\mathrm{O}_2$, which is $32 \mathrm{~g}$. Thus, the required equation of state is $\mathrm{PV}=\frac{1}{4} \mathbf{R T}$.
Question 26.
At a given volume and temperature, the pressure of a gas ....
(a) varies inversely as its mass
(b) varies inversely as the square of its mass
(c) varies linearly as its mass
(d) is independent of its mass
Answer:
(c) varies linearly as its mass
Question 27.
Oxygen boils at $-183^{\circ} \mathrm{C}$. This temperature in Fahrenheit scale is
(a) $-215.7^{\circ}$
(b) $-297.4^{\circ}$
(c) $-310.6^{\circ}$
(d) $-373.2^{\circ}$
Answer:
(b) $-297.4^{\circ}$
Solution:
$
\frac{\mathrm{F}-32}{9}=\frac{\mathrm{C}}{5} \Rightarrow \mathrm{F}=32+\frac{9}{5}(-183) \Rightarrow \mathrm{F}=-297.4^{\circ} \mathrm{F}
$
Question 28.
A centigrade and a Fahrenheit thermometer are dipped in boiling water. The water temperature is lowered until the Fahrenheit thermometer registers $140^{\circ}$. What is the decrease in temperature as registered by the centigrade thermometer?
(a) $80^{\circ}$
(b) $60^{\circ}$

(c) $40^{\circ}$
(d) $30^{\circ}$
Answer:
(c) $40^{\circ}$
Solution:
$
\frac{\Delta \mathrm{C}}{5}=\frac{\Delta \mathrm{F}}{9} \Rightarrow \Delta \mathrm{C}=\frac{5}{9} \Delta \mathrm{F}=\frac{5}{9}(212-140) \Rightarrow \Delta \mathrm{C}=40^{\circ} \mathrm{C}
$
Question 29.
The change in temperature of a body is $50^{\circ} \mathrm{C}$. The change on the kelvin scale is
(a) $50 \mathrm{~K}$
(b) $323 \mathrm{~K}$
(c) $70 \mathrm{~K}$
(d) $30 \mathrm{~K}$
Answer:
(a) $50 \mathrm{~K}$

Question 30 .
Mercury thermometers can be used to measure temperature up to ........
(a) $260^{\circ} \mathrm{C}$
(b) $100^{\circ} \mathrm{C}$
(c) $360^{\circ} \mathrm{C}$
(d) $500^{\circ} \mathrm{C}$
Answer:
(c) $360^{\circ} \mathrm{C}$
Question 31.
For an ideal gas the inter particle interaction is
(a) attractive
(b) repulsive
(c) very large
(d) zero
Answer:
(d) zero
Question 32.
Device used to measure very high temperature is .......
(a) Pyrometer
(b) Thermometer
(c) Bolometer
(d) calorimeter
Answer:
(a) Pyrometer
Question 33.
Two metal rods A and $\mathrm{B}$ are having their initial lengths in the ratio $2: 3$, and coefficients of linear expansion in the ratio $3: 4$. When they are heated through same temperature difference,the ratio of their linear expansions is ......
(a) $1: 2$

(b) $2: 3$
(c) $3: 4$
(d) $4: 3$
Answer:
(a) $1: 2$
Solution: $\Delta l_{\mathrm{A}}=l_{\mathrm{A}} \alpha_{\mathrm{A}} \Delta t ; \Delta l_{\mathrm{B}}=l_{\mathrm{B}} \alpha_{\mathrm{B}} \Delta t$
$
\frac{\Delta l_{\mathrm{A}}}{\Delta l_{\mathrm{B}}}=\frac{l_{\mathrm{A}} \alpha_{\mathrm{A}}}{l_{\mathrm{B}} \alpha_{\mathrm{B}}}=\frac{2}{3} \times \frac{3}{4}=\frac{1}{2} \Rightarrow \Delta l_{\mathrm{A}}: \Delta l_{\mathrm{B}}=1: 2
$
Question 34.
Boyles' law is applicable in ......
(a) isochoric process
(b) isothermal process
(c) isobaric process
(d) both (a) and (b)
Answer:
(b) isothermal process

Question 35.
A rod, when heated from $0^{\circ} \mathrm{C}$ to $50^{\circ} \mathrm{C}$, expands by $1.0 \mathrm{~mm}$. Another rod, twice as long as the first at $0^{\circ} \mathrm{C}$ and of the same material, is heated from $0^{\circ} \mathrm{C}$ to $25^{\circ} \mathrm{C}$. The second rod will expand by $\ldots \ldots$
(a) $0.5 \mathrm{~mm}$
(b) $1.0 \mathrm{~mm}$
(c) $2.0 \mathrm{~mm}$
(d) $4.0 \mathrm{~mm}$
Answer:
(b) $1.0 \mathrm{~mm}$
Solution: $\Delta l=l_o \alpha \Delta t$
$
\frac{\Delta l_2}{\Delta l_1}=\frac{2 l_o \Delta t_2}{l_o \Delta t_1} \Rightarrow \Delta l_2=\frac{2 \times 25}{50} \times 1.0 \Rightarrow \Delta l_2=1.0 \mathrm{~mm}
$
Question 36.
A container contains hydrogen gas at pressure $P$ and temperature $T$. Another identical container contains helium gas at pressure $2 \mathrm{P}$ and temperature $\mathrm{T} / 2$. The ratio of the number of molecules of the two gases is
(a) $1: 4$
(b) $4: 1$
(c) $1: 2$
(d) $2: 1$
Answer:
(a) $1: 4$
Solution:
The ratio of the number of molecules is same as the ratio of the number of moles.

Now $\mathrm{n}=\frac{P V}{R T}$
$
\frac{n_{\mathrm{H}_2}}{n_{\mathrm{He}}}=\frac{\mathrm{PV}}{\mathrm{RT}} \times \frac{\mathrm{R}\left(\frac{\mathrm{T}}{2}\right)}{(2 \mathrm{P}) \mathrm{V}}=\frac{1}{4} \Rightarrow \quad n_{\mathrm{H}_2}: n_{\mathrm{He}}=1: 4
$
Question 37.
Density of water is maximum at the temperature of
(a) $32^{\circ} \mathrm{F}$
(b) $39.2^{\circ} \mathrm{F}$
(c) $42^{\circ} \mathrm{F}$
(d) $40^{\circ} \mathrm{F}$
Answer:
(b) $39.2^{\circ} \mathrm{F}$
Solution:
The density of water is maximum at $4^{\circ} \mathrm{C}$. Let $\mathrm{F}$ be the corresponding temperature on the Fahrenheit scale. Then using the equation
$
\frac{\mathrm{F}-32}{9}=\frac{\mathrm{C}}{5}=\frac{4}{5} \Rightarrow \mathrm{F}=39.2^{\circ} \mathrm{F}
$
Question 38 .
The equation of state for $5 \mathrm{~g}$ of oxygen at a pressure $P$ and temperature $T$, when occupying a volume $\mathrm{V}$, is ( $\mathrm{R}$ is the gas constant)
(a) $\mathrm{PV}=(5 / 32) \mathrm{RT}$
(b) $\mathrm{PV}=5 \mathrm{RT}$
(c) $\mathrm{PV}=(5 / 2) \mathrm{RT}$
(d) $\mathrm{PV}=(5 / 16) \mathrm{RT}$
Answer:
(a) $\mathrm{PV}=(5 / 32) \mathrm{RT}$

Solution:
Number of moles, $\mathrm{n}=\frac{5}{32}$
Question 39.
A bimetallic strip consists of metals $\mathrm{X}$ and $\mathrm{Y}$. It is mounted rigidly at the base as shown. The metal $\mathrm{X}$ has a higher coefficient of expansion compared to that for metal $\mathrm{Y}$. When the bimetallic strip is placed in a cold bath?

(a) it will bend towards the right
(b) it will bend towards the left
(b) it will not bend but shrink
(d) it will neither bend nor shrink
Answer:
(b) it will bend towards the left.
Solution:
In cold bath, the metal $\mathrm{X}$ will contract more than the metal $\mathrm{Y}$. Therefore, the strip will bend towards the left.
Question 40.
An ideal gas is expanding such that $\mathrm{PT}^2=$ constant the coefficient of volume expansion of the gas is
(a) $\frac{1}{\mathrm{~T}}$
(b) $\frac{2}{\mathrm{~T}}$
(c) $\frac{3}{\mathrm{~T}}$
(d) $\frac{4}{\mathrm{~T}}$
Answer:
$\frac{3}{\mathrm{~T}}$
Solution:
Coefficient of volume expansion $\alpha_{\mathrm{v}}=\frac{d \mathrm{~V}}{\mathrm{v} d \mathrm{~T}}$

$\mathrm{PT}^2=\mathrm{K}$ and $\mathrm{PV}=\mathrm{nRT}$
$
\frac{\mathrm{T}^2}{\mathrm{~V}}=\frac{\mathrm{K}}{n \mathrm{RT}} \Rightarrow \frac{\mathrm{KV}}{n \mathrm{R}}=\mathrm{T}^3
$
Differentiating, $\frac{\mathrm{T}^3}{\mathrm{~V}} d \mathrm{~V}=3 \mathrm{~T}^2 d \mathrm{~T} \Rightarrow \alpha_{\mathrm{V}}=\frac{d \mathrm{~V}}{d \mathrm{~T}}=\frac{3}{\mathrm{~T}}$
Question 41.
A metallic solid sphere is rotating about its diameter as axis of rotation. If the temperature is increased by $200^{\circ} \mathrm{C}$, the percentage increase in its moment of inertia is : (coefficient of linear expansion of the metal $=10^{-5} /{ }^{\circ} \mathrm{C}$ )
(a) 0.1
(b) 0.2
(c) 0.3
(d) 0.4
Answer:
(d) 0.4
Solution:
$
\begin{aligned}
\mathrm{I} & =\frac{2}{5} \mathrm{MR}^2 \\
\frac{\Delta \mathrm{I}}{\mathrm{I}} & =2 \frac{\Delta \mathrm{R}}{\mathrm{R}}=\frac{2 \mathrm{R} \alpha \Delta t}{\mathrm{R}}=2 \alpha \Delta t \\
\frac{\Delta \mathrm{I}}{\mathrm{I}} & =2 \times 10^{-5} \times 200=4 \times 10^{-3}
\end{aligned}
$
Percentage increase $=4 \times 10^{-3} \times 100=0.4$

Question 42.
The difference between volume and pressure coefficients of an ideal gas is
(a) $\frac{1}{273}$
(b) 273
(c) $\frac{2}{273}$
(d) zero
Answer:
(d) Zero
Question 43.
Which of the following instruments is used in the measurement of temperatures above $2000^{\circ} \mathrm{C}$ ?
(a) Gas thermometer
(b) Pyrometer
(c) Bolometer
(d) Thermo-electric Pile
Answer:
(b) Pyrometer
Question 44.
At $0^{\circ} \mathrm{C}$, Pressure measured by barometer is $760 \mathrm{~mm}$. What will be the pressure at $100^{\circ} \mathrm{C}$ ?
(a) 760
(b) 730
(c) 780
(d) none of these
Answer:
(d) none of these
Solution: $\frac{P_2}{T_2}=\frac{P_1}{T_1} \Rightarrow P_2=\frac{P_1 T_2}{T_1}=\frac{760 \times 373}{273} \Rightarrow P_2=1038 \mathrm{~mm}$
Question 45.
The temperature on the new scale, corresponding to a temperature of $39^{\circ} \mathrm{C}$ on the Celsius scale?
(a) $73^{\circ} \mathrm{W}$

(b) $117^{\circ} \mathrm{W}$
(c) $200^{\circ} \mathrm{W}$
(d) $139^{\circ} \mathrm{W}$
Answer:
(b) $117^{\circ} \mathrm{W}$
Solution:
Let $t$ be the required temperature. Then,
$
\frac{t-39}{239-39}=\frac{39-0}{100-0} \Rightarrow t=117^{\circ} \mathrm{W}
$
Question 46.
Two balloons are filled, one with pure He gas and the other with air. If the pressure and temperature in both the balloons are same the number of molecules per unit volume is
(a) more in the He filled balloon
(b) more in the air filled balloon.
(c) same in both the balloon.
(d) in the ratio $1: 4$.
Answer:
(c) same in both the balloons.

Solution: Assuming ideal gas behavior, the number of moles per unit volume is $\frac{n}{V}=\frac{P}{R T}$ Since $P$ and $\mathrm{T}$ are same in both the balloon, $\frac{n}{V}$ is also same in both.
Question 47.
Pressure of an ideal gas is increased by keeping temperature constant. What is the effect on the kinetic energy of molecules?
(a) increase
(b) no change
(c) decrease
(d) can't be determined
Answer:
(b) no change
Solution:
K.E of an ideal gas depends only on the temperature. Hence, it remains the same.
Question 48 .
One mole of gas occupies a volume of $200 \mathrm{ml}$. at $100 \mathrm{~mm}$ pressure. What is the volume occupied by two moles of this gas at $400 \mathrm{~mm}$ pressure and at same temperature?
(a) $50 \mathrm{ml}$
(b) $100 \mathrm{ml}$
(c) $200 \mathrm{ml}$
(d) $400 \mathrm{ml}$
Answer:
(b) $100 \mathrm{ml}$
Solution:
$
\begin{aligned}
& \mathrm{V}_2=\frac{\mathrm{P}_1 \mathrm{~V}_1}{\mathrm{P}_2}=\frac{100 \times 200}{400}=50 \mathrm{ml} \\
& \Rightarrow \text { Volume of } 2 \text { moles of the gas at } 400 \mathrm{~mm} \text { pressure }=2 \times 50=100 \mathrm{ml}
\end{aligned}
$

Question 49.
There is a change in length when a $33000 \mathrm{~N}$ tensile force is applied on a steel rod of area of cresssection $10^{-3} \mathrm{~m}^2$. The change of temperature required to produce the same elongation, if the steel rod is heated, is (modulus of elasticity of steel $=3 \times 10^{11} \mathrm{~N} / \mathrm{m}^2$, coefficient of linear expansion of steel $\left.=1.1 \times 10^{-5} /{ }^{\circ} \mathrm{C}\right)$
(a) $20^{\circ} \mathrm{C}$
(b) $15^{\circ} \mathrm{C}$
(c) $10^{\circ} \mathrm{C}$
(d) $0^{\circ} \mathrm{C}$
Answer:
(c) $10^{\circ} \mathrm{C}$
Solution:
$
\begin{aligned}
& \Delta l=\alpha l \Delta t=\frac{\mathrm{F} l}{\mathrm{AY}} \\
& \Delta t=\frac{\mathrm{F} l}{\alpha \mathrm{AY}}=\frac{33000}{1.1 \times 10^{-5} \times 10^{-3} \times 3 \times 10^{11}} \Rightarrow \Delta t=10^{\circ} \mathrm{C}
\end{aligned}
$

Question 50.
In the given $(\mathrm{V}-\mathrm{T})$ diagram, what is the relation between pressures $P_1$ and $P_2$ ?
(a) $P_2=P_1$
(b) $\mathrm{P}_2>\mathrm{P}_1$
(c) $\mathrm{P}_2<\mathrm{P}_1$
(d) cannot be predicted
Answer:
(c) $P_2

Solution: $\mathrm{PV}=n \mathrm{RT} \Rightarrow \mathrm{V}=\left(\frac{n \mathrm{R}}{\mathrm{P}}\right) \mathrm{T}$
This shows that slope of the graph $\propto \frac{1}{\mathrm{P}}$ Hence $\mathrm{P}_2<\mathrm{P}_1$
Question 51.
Boiling water is changing into steam. Under this condition the specific heat of water is
(a) zero
(b) one
(c) infinite
(d) less than one
Answer:
(c) infinite
Solution:
In order to change boiling water into steam, heat has to be given but there is no increase of temperature. Therefore, under this condition the specific heat of water is infinite.
Question 52.
The first law of thermodynamics is concerned with the conservation of
(a) number of molecules
(b) energy

(c) number of moles
(d) temperature
Answer:
(b) energy
Question 53.
The gas law $\frac{P V}{T}=$ constant is true for
(a) isothermal changes only
(b) adiabatic changes only
(c) both isothermal and adiabatic changes
(d) neither isothermal nor adiabatic changes
Answer:
(c) both isothermal and adiabatic changes
Question 54 .
The pressure-temperature relationship for an ideal gas undergoing adiabatic change is .....
(a) $\mathrm{P}^{1-\gamma} \mathrm{T}^\gamma=$ constant
(b) $\mathbf{P}^{\gamma-1} \mathrm{~T}^\gamma=$ constant
(c) $\mathrm{P}^\gamma \mathrm{T}^{1-\gamma}=$ constant
(d) $\mathrm{P}^\gamma \mathrm{T}^{\gamma-1}=$ constant
Answer:
(a) $\mathrm{p}^{1-\gamma} \mathrm{T}^\gamma=$ constant
Question 55.
For a certain gas the ratio of specific heats is given to be $\gamma=1.5$. For this gas .......
(a) $\mathrm{C}_{\mathrm{V}}=3 \mathrm{R}$
(b) $\mathrm{C}_{\mathrm{P}}=3 R$
(c) $\mathrm{C}_{\mathrm{V}}=5 \mathrm{R}$
(d) $C_P=5 R$
Answer:
(b) $C_P=3 R$
Solution:
$
\frac{C_P}{C_V}=\frac{3}{2} \Rightarrow C_V=\frac{2}{3} C_P
$
Now,
$
\mathrm{C}_{\mathrm{P}}-\mathrm{C}_{\mathrm{V}}=\mathrm{R} \Rightarrow \mathrm{C}_{\mathrm{P}}-\frac{2}{3} \mathrm{C}_{\mathrm{P}}=\mathrm{R} \Rightarrow \mathrm{C}_{\mathrm{P}}=3 \mathrm{R}
$
Question 56.
Cooking takes longest time
(a) at the sea level
(b) at Shimla
(c) at mount Everest (if tried)
(d) in a submarine $100 \mathrm{~m}$ below the surface of water.
Answer:
(c) at mount Everest (if tried)
Question 57.
A closed bottle containing water at room temperature is taken to the moon and then the lid is opened. The water will ......
(a) freeze

(b) boil
(c) decompose into hydrogen and oxygen
(d) not change at all.
Answer:
(b) boil
Solution:
There is no atmosphere on the moon and so there is no pressure
Quarter 58.
A gas receives an amount of heat equal to 110 joules and performs 40 joules of work. The change in the internal energy of the gas is ......
(a) $70 \mathrm{~J}$
(b) $150 \mathrm{~J}$
(c) $110 \mathrm{~J}$
(d) $40 \mathrm{~J}$
Answer:
(a) $70 \mathrm{~J}$
Question 59.
For a mono-atomic gas, the molar specific heat at constant pressure divided by the molar gas constant $R$, is equal to .....
(a) 2.5
(b) 1.5
(c) 5.0
(d) 3.5
Answer:
(a) 2.5
Question 60.
Heat capacity of a substance is infinite. It means .......
(a) infinite heat is given out

(b) infinite heat is taken in
(c) no change in temperature whether heat is taken in or given out
(d) all of these
Answer:
(c) no change in temperature whether heat is taken in or given out
Solution: Heat $\quad \mathrm{H}=m c \Delta \theta ; c=\frac{\mathrm{H}}{m \Delta \theta}$
If $\Delta \theta=0$ then $c=\infty$
Question 61
We consider a thermodynamic system. If $\Delta \mathrm{U}$ represent the increase in its energy and $\mathrm{W}$ the work done by the system, which of the following statements is true?
(a) $\Delta \mathrm{U}=-\mathrm{W}$ in an isothermal process
(b) $\Delta \mathrm{U}=-\mathrm{W}$ in an adiabatic process
(c) $\Delta \mathrm{U}=\mathrm{W}$ in an isothermal process
(d) $\Delta \mathrm{U}=\mathrm{W}$ in an adiabatic process
Answer:
(b) $\Delta \mathrm{U}=-\mathrm{W}$ in an adiabatic process
Solution:
According to the first law of thermodynamics $\Delta \mathrm{Q}=\mathrm{AU}+\mathrm{W}$

In an adiabatic process, $\Delta \mathrm{Q}=0$. Therefore, $\Delta \mathrm{U}=-\mathrm{W}$
Question 62.
The first operation involved in a carnot cycle is
(a) isothermal expansion
(b) adiabatic expansion
(c) isothermal compression
(d) adiabatic compression
Answer:
(a) isothermal expansion
Question 63.
During an adiabatic process, if the pressure of an ideal gas is proportional to the cube of its temperature, the ratio $\gamma=\frac{\mathrm{C}_{\mathrm{P}}}{\mathrm{C}_{\mathrm{V}}}$ is $\ldots$.
(a) 2
(b) $\frac{4}{3}$
(c) $\frac{5}{3}$
(d) $\frac{3}{2}$
Answer:
(d) $\frac{3}{2}$
Solution:
For an adiabatic process $\mathrm{P} \propto \frac{\gamma}{\frac{\gamma}{\gamma-1}}$
$
\frac{\gamma}{\gamma-1}=3 \Rightarrow \gamma=\frac{3}{2}
$
Question 64.
In a given process on an ideal gas, $\mathrm{dW}=0$ and $\mathrm{dQ}<0$. Then for the gas .......
(a) The temperature will decrease.
(b) the volume will decrease.

(c) the pressure will remain constant.
(d) the temperature will increase.
Answer:
(a) The temperature will decrease.
Solution:
According to the first law of thermodynamics, the internal energy decreases. Hence the temperature will decrease.
Question 65.
In a carnot heat engine $8000 \mathrm{~J}$ of heat is absorbed from a source at $400 \mathrm{~K}$ and $6500 \mathrm{~J}$ of heat is
rejected to the sink. The temperature of the sink is
(a) $325 \mathrm{~K}$
(b) $100 \mathrm{~K}$
(c) $200 \mathrm{~K}$
(d) $273 \mathrm{~K}$
Answer:
(a) $325 \mathrm{~K}$
Solution: We have, $\frac{T_2}{T_1}=\frac{Q_2}{Q_1} \Rightarrow T_2=\frac{Q_2}{Q_1} T_1=\frac{6500}{8000} \times 400 \Rightarrow T_2=325 \mathrm{~K}$

Question 66 .
$2 \mathrm{Kg}$ of water of $60^{\circ} \mathrm{C}$ is mixed with $1 \mathrm{~kg}$ of water at $30^{\circ} \mathrm{C}$ kept in a vessel of heat capacity $220 \mathrm{~J} \mathrm{~K}^{-}$ 1 . The specific heat of water is $4200 \mathrm{~J} \mathrm{Kg}-1 \mathrm{~K}$. Then the final temperature is nearly.
(a) $35^{\circ} \mathrm{C}$
(b) $45^{\circ} \mathrm{C}$
(c) $55^{\circ} \mathrm{C}$
(d) $50^{\circ} \mathrm{C}$
Answer:
(d) $50^{\circ} \mathrm{C}$
Solution:
According to the principle of calorimetry,
$
2 \times 4200 \times(60-\theta)=(1 \times 4200+200)(\theta-30) \Rightarrow \theta=50^{\circ} \mathrm{C}
$
Question 67.
A carnot engine absorbs heat at $127^{\circ} \mathrm{C}$ and rejects heat at $87^{\circ} \mathrm{C}$. The efficiency of engine is
(a) $10 \%$
(b) $30 \%$
(c) $50 \%$
(d) $70 \%$
Answer:
(a) $10 \%$
Solution:
$
\eta=1-\frac{\mathrm{T}_2}{\mathrm{~T}_1}=1-\frac{360}{400}=\frac{1}{10}=10 \%
$

Question 68 .
The first law of thermodynamics confirms the law of
(a) conservation of momentum
(b) conservation of energy
(c) flow of heat in a particular direction
(d) conservation of heat energy and mechanical energy
Answer:
(b) conservation of energy
Question 69.
The internal energy of an ideal gas depends on
(a) only pressure
(b) only volume
(c) only temperature
(d) none of these
Answer:
(c) only temperature

Question 70.
An ideal gas heat engine operators in a carnot's cycle between $227^{\circ} \mathrm{C}$ and $127^{\circ} \mathrm{C}$. It absorbs $6 \times 10^4 \mathrm{~J}$ at high temperature. The amount of heat converted into work is
(a) $2.4 \times 10^4 \mathrm{~J}$
(b) $4.8 \times 10^4 \mathrm{~J}$
(c) $1.2 \times 10^4 \mathrm{~J}$
(d) $6 \times 10^4 \mathrm{~J}$
Answer:
(c) $1.2 \times 10^4 \mathrm{~J}$
Solution:
$
\begin{aligned}
& \frac{W}{Q}=1-\frac{T_2}{T_1} \\
& W=\left(1-\frac{273+127}{273+227}\right) \times 6 \times 10^4=1.2 \times 10^4 \mathrm{~J}
\end{aligned}
$
Question 71.
In an isochoric process
(a) $\Delta \mathrm{U}=\Delta \mathrm{Q}$
(b) $\Delta \mathrm{Q}=\Delta \mathrm{W}$
(c) $\Delta \mathrm{U}=\Delta \mathrm{W}$
(d) None of these
Answer:
(a) $\Delta \mathrm{U}=\Delta \mathrm{Q}$
Solution:
In an isochoric process, volume remains constant. Therefore, no work is done by or on the system. So, $\Delta \mathrm{W}=0$ Hence $\Delta \mathrm{U}=\Delta \mathrm{Q}$.

Question 72.
The molar specific heat at constant pressure of an ideal gas is $(7 / 2) \mathrm{R}$. The ratio specific heats at constant pressure to that at constant volume is ........
(a) $8 / 7$
(b) $5 / 7$
(c) $9 / 7$
(d) $7 / 5$
Answer:
(d) $7 / 5$
Solution:
$
\mathrm{C}_{\mathrm{P}}=\frac{7}{2} \mathrm{R} ; \mathrm{C}_{\mathrm{V}}=\frac{7}{2} \mathrm{R}-\mathrm{R}=\frac{5}{2} \mathrm{R} ; \gamma=\frac{\mathrm{C}_{\mathrm{P}}}{\mathrm{C}_{\mathrm{V}}}=\frac{7}{5}
$
Question 73.
If energy dQ is supplied to a gas isochorically, increase in internal energy is dU. Then ....
(a) $\mathrm{dQ}>\mathrm{dU}$
(b) $\mathrm{dQ}<\mathrm{dU}$
(c) $\mathrm{dQ}=\mathrm{dU}$
(d) $\mathrm{dQ}=-\mathrm{dU}$

Answer:
(c) $\mathrm{dQ}=\mathrm{dU}$
Question 74.
A diatomic ideal gas is used in a camot engine as the working substance. If during the adiabatic expansion part of the cycle, the volume of the gas increases from $\mathrm{V}$ to $32 \mathrm{~V}$, the efficiency of the engine is .....
(a) 0.25
(b) 0.5
(c) 0.75
(d) 0.99
Answer:
(c) 0.75
Solution: $\quad \mathrm{TV}^{\gamma-1}=$ constant
$
\begin{aligned}
& \Rightarrow \quad \frac{T_2}{T_1}=\left(\frac{V_1}{V_2}\right)^{\gamma-1}=\left(\frac{1}{32}\right)^{\frac{7}{5}-1} \\
& \frac{\mathrm{T}_2}{\mathrm{~T}_1}=\left(\frac{1}{2^5}\right)^{\frac{2}{5}}=\frac{1}{4} \\
&
\end{aligned}
$
Efficiency $\quad \eta=1-\frac{T_2}{T_1}=1-\frac{1}{4}=0.75$
Question 75.
The mechanical equivalent of heat $\mathrm{J}$ is:
(a) a constant
(b) a physical quantity
(c) a conversion factor

(d) none of the above
Answer:
(c) a conversion factor
Question 76.
Which of the following process is reversible?
(a) transfer of heat by radiation
(b) Transfer of heat by conduction
(c) Electrical heating of nichrome wire
(d) Isothermal compression
Answer:
(d) Isothermal compression
Question 77.
An ideal gas heat engine operates in camot cycle between $227^{\circ} \mathrm{C}$ and $127^{\circ} \mathrm{C}$. It absorbs $6 \times 10^4 \mathrm{cal}$ of heat converted to work is .....
(a) $1.2 \times 10^4 \mathrm{cal}$
(b) $4.8 \times 10^4 \mathrm{cal}$

(c) $6 \times 10^4 \mathrm{cal}$
(d) $2.4 \times 10^4 \mathrm{cal}$
Answer:
(a) $1.2 \times 10^4 \mathrm{cal}$
Solution: $\quad$ Efficiency $=\frac{\mathrm{W}}{\mathrm{Q}}=1-\frac{\mathrm{T}_2}{\mathrm{~T}_1}=1-\frac{(273+127)}{(273+227)}=\frac{1}{5}$
$
\mathrm{W}=\frac{1}{5} \times 6 \times 10^4=1.2 \times 10^4 \mathrm{Cal}
$
Question 78.
Ten moles of an ideal gas at constant temperature $600 \mathrm{~K}$ is compressed from 1001 to $10 \mathrm{~L}$. The work done in the process is .....
(a) $4.11 \times 10^4 \mathrm{~J}$
(b) $-4.11 \times 10^4 \mathrm{~J}$
(c) $11.4 \times 10^4 \mathrm{~J}$
(d) $-11.4 \times 10^4 \mathrm{~J}$
Answer:
(d) $-11.4 \times 10^4 \mathrm{~J}$
Solution:
The process is isothermal. The work done is,
$
\mathrm{W}=n \mathrm{RT} \ln \left(\frac{\mathrm{V}_2}{\mathrm{~V}_1}\right)=2.3026 \times 10 \times 8.3 \times 600 \times \log _{10}\left(\frac{10}{100}\right) \Rightarrow \mathrm{W}=-11.4 \times 10^4 \mathrm{~J}
$
Question 79.
A gas is compressed at a constant pressure of $50 \mathrm{~N} / \mathrm{m}^2$ from a volume $4 \mathrm{~m}^3$. Energy of $100 \mathrm{~J}$ is then added to the gas by heating. Its internal energy is .....
(a) increased by $400 \mathrm{~J}$

(b) increased by $200 \mathrm{~J}$
(c) increased by $100 \mathrm{~J}$
(d) decreased by $200 \mathrm{~J}$
Answer:
(a) increased by $400 \mathrm{~J}$
Solution:
$
\Delta \mathrm{U}=\Delta \mathrm{Q}-\Delta \mathrm{W}=\Delta \mathrm{Q}-\mathrm{P} \Delta \mathrm{V}=100-50(4-10)=400 \mathrm{~J}
$
Question 80 .
If $\mathrm{Q}, \mathrm{E}$ and $\mathrm{W}$ denote respectively the heat added, change in internal energy and the work done in a closed cyclic process, then ......
(a) $\mathrm{W}=0$
(b) $\mathrm{Q}=\mathrm{W}=\mathrm{O}$
(c) $\mathrm{E}=0$
(d) $\mathrm{Q}=0$
Answer:
(c) $\mathrm{E}=0$
Solution:
In a cyclic process, a system starts in one state and comes back to the same state. Therefore, the change in internal energy is zero.

Question 81.
A carnot engine takes heat from a reservoir at $627^{\circ} \mathrm{C}$ and rejects heat to a sink at $27^{\circ} \mathrm{C}$. Its efficiency is
(a) $3 / 5$
(b) $1 / 3$
(c) $2 / 3$
(d) 200/209
Answer:
(c) $2 / 3$
Question 82.
A carnot engine operates with source at $127^{\circ} \mathrm{C}$ and sink at $27^{\circ} \mathrm{C}$. If the source supplies $40 \mathrm{KJ}$ of heat energy, the work done by the engine is
(a) $1 \mathrm{KJ}$
(b) $4 \mathrm{KJ}$
(c) $10 \mathrm{KJ}$
(d) $30 \mathrm{KJ}$
Answer:
(c) $10 \mathrm{KJ}$
Solution:
$
\frac{W}{Q_1}=1-\frac{T_2}{T_1} \Rightarrow W=\left(1=\frac{300}{400}\right) \times 40=10 \mathrm{~kJ}
$
Question 83.
The ratio of the specific heat $\frac{\mathrm{C}_{\mathrm{p}}}{\mathrm{C}_v}=\gamma$ in term of degrees of freedom $(\mathrm{n})$ is given by:

(a) $\left(1+\frac{n}{3}\right)$
(b) $\left(1+\frac{2}{n}\right)$
(c) $\left(1+\frac{n}{2}\right)$
(d) $\left(1+\frac{1}{n}\right)$
Answer:
(b) $\left(1+\frac{2}{n}\right)$
Solution:
$
\mathrm{C}_{\mathrm{V}}=\frac{n}{2} \mathrm{R} ; \mathrm{C}_{\mathrm{P}}=\left(\frac{n}{2}+1\right) \mathrm{R} \Rightarrow \frac{\mathrm{C}_{\mathrm{P}}}{\mathrm{C}_{\mathrm{V}}}=\left(1+\frac{2}{n}\right)
$
Question 84.
The heat required to increase the temperature of 4 moles of a mono-atomic ideal gas from $273 \mathrm{~K}$ to $473 \mathrm{~K}$ constant volume is ....
(a) $200 \mathrm{R}$
(b) $400 \mathrm{R}$
(c) $800 \mathrm{R}$
(d) $1200 \mathrm{R}$
Answer:
(d) $1200 \mathrm{R}$
Solution:
Heat required $=n \mathrm{C}_{\mathrm{v}} \Delta \mathrm{T}=4 \times \frac{3}{2} \mathrm{R} \times(473-273)=1200 \mathrm{R}$
Question 85 .
The coefficient of performance of a refrigerator is 5 . If the temperature inside freezer is $-20^{\circ} \mathrm{C}$, the temperature of the surroundings to which it rejects heat is
(a) $21^{\circ} \mathrm{C}$
(b) $31^{\circ} \mathrm{C}$
(c) $41^{\circ} \mathrm{C}$

(d) $11^{\circ} \mathrm{C}$
Answer:
(b) $31^{\circ} \mathrm{C}$
Solution: Coefficient of performance, $K=\frac{T_2}{T_1-T_2}$
$
\begin{aligned}
\mathrm{T}_1 & =\left(\frac{\mathrm{K}+1}{\mathrm{~K}}\right) \mathrm{T}_2=\frac{6}{5} \times 253=303.6 \mathrm{~K} \\
\mathrm{~T}_1 & =30.6^{\circ} \mathrm{C}
\end{aligned}
$
II. Write brief answer to the following questions:
Question 1.
What is meant by 'heat'?
Answer:
When an object at higher temperature is placed in contact with another object at lower temperature, there will be a spontaneous flow of energy from the object at higher temperature to the one at lower temperature. This energy is called heat.

Question 2.
What is meant by 'temperature'? Give its unit.
Answer:
Temperature is the degree of hotness or coolness of a body. Hotter the body higher is its temperature. The temperature will determine the direction of heat flow when two bodies are in thermal contact. The SI unit of temperature is kelvin (K).
Question 3.
Define Avogadro's number $\mathrm{N}_{\mathrm{A}}$ ?
Answer:
The Avogadro's number $\mathrm{N}_{\mathrm{A}}$ is defined as the number of carbon atoms contained in exactly $12 \mathrm{~g}$ of ${ }^{12} \mathrm{C}$
Question 4.
Define heat capacity (or) thermal capacity?
Answer:
The heat capacity of a body is defined as the amount of heat required to raise its temperature through one degree.
Question 5.
What is meant by 'Triple point of a substance'?
Answer:
The triple point of a substance is the temperature and pressure at which the three phases (gas, liquid and solid) of that substance coexist in thermodynamic equilibrium.
Question 6.
What do you meant by change of state of a substance?
Answer:
The transition of a substance from one state to another by heating or cooling it is called change of state.

Question 7.
Define coefficient of linear expansion. Give its unit.
Answer:
The coefficient of linear expansion of the material of a solid rod is defined as the increase in length per unit original length per degree rise in its temperature.
The unit of $\alpha_{\mathrm{L}}$ is ${ }^{\circ} \mathrm{C}^{-1}$ (or $\mathrm{KT}^{-1}$ )
Question 8 .
Define coefficient of area expansion? Give its unit.
Answer:
The coefficient of area expansion of a metal sheet is defined as the increase in its surface area per
unit original surface area per degree rise in its temperature.
The unit of $\alpha_{\mathrm{A}}$ is ${ }^{\circ} \mathrm{Ca}^{-1}$ (or) $\mathrm{KT}^{-1}$
Question 9.
Define coefficient of Volume expansion? Give its unit.
Answer:
The coefficient of Volume expansion of a substance is defined as the increase in volume per unit original volume per degree rise in its temperature.
The unit of $\alpha_{\mathrm{v}}$ is ${ }^{\circ} \mathrm{C}^{-1}$ (or) $\mathrm{KT}^{-1}$
Question 10.
What is meant by conduction?
Answer:
Conduction is the process of direct transfer of heat through matter due to temperature difference. When two objects are in direct contact with one another, heat will be transferred from the hotter object to the colder one. The objects which allow heat to travel easily through them are called conductors.
Question 11.
What is meant by Convection?
Answer:
Convection is the process in which heat transfer is by actual movement of molecules in fluids such as liquids and gases. In convection, molecules move freely from one place to another.
Question 12.
What is meant by Radiation? Give example.
Answer:
Radiation is a form of energy transfer from one body to another by electromagnetic waves.
Example:
1. Solar energy from the Sun.
2. Radiation from room heater.
Question 13.
State Newton's Law of cooling.
Answer:
Newton's law of cooling states that the rate of loss of heat of a body is directly proportional to the difference in the temperature between that body and its surroundings.

Question 14.
What do you meant by absolute zero of temperature?
Answer:
The lowest temperature of $0 \mathrm{~K}$ at which a gas is supposed to have zero volume (and zero pressure) and at which entire molecular motion stops is called absolute zero of temperature.
Question 15.
State Prevost theory of heat exchange.
Answer:
Prevost theory states that all bodies emit thermal radiation at all temperatures above absolute zero irrespective of the nature of the surroundings.
Question 16.
What is meant by 'Mechanical equilibrium'?
Answer:
A system is said to be in mechanical equilibrium if no unbalanced force acts on the thermo dynamic system or on the surrounding by thermodynamic system.

Question 17.
What is meant by 'chemical equilibrium'?
Answer:
Chemical equilibrium: If there is no net chemical reaction between two thermodynamic systems in contact with each other then it is said to be in chemical equilibrium.
Question 18.
What is meant by 'thermodynamic equilibrium'.
Answer:
In a state of thermodynamic equilibrium the macroscopic variables such as pressure, volume and temperature will have fixed values and do not change with time.
Question 19.
Briefly explain how such a quasi-static process can be carried out.
Answer:
Quasi-static process: Consider a system of an ideal gas kept in a cylinder of volume $\mathrm{V}$ at pressure $\mathrm{P}$ and temperature $T$. When the piston attached to the cylinder moves outward the volume of the gas will change. As a result the temperature and pressure will also change because all three variables $\mathrm{P}, \mathrm{T}$ and $\mathrm{V}$ are related by the equation of state $\mathrm{PV}=\mathrm{NkT}$. If a block of some mass is kept on the piston, it will suddenly push the piston downward. The pressure near the piston will be larger than other parts of the system. It implies that the gas is in non-equilibrium state. We cannot determine pressure, temperature or internal energy of the system until it reaches another equilibrium state. But if the piston is pushed very slowly such that at every stage it is still in equilibrium with surroundings, we can use the equation of state to calculate the internal energy, pressure or temperature. This kind of process is called quasi-static process.
A quasi-static process is an infinitely slow process in which the system changes its variables $(\mathrm{P}, \mathrm{V}, \mathrm{T})$ so slowly such that it remains in thermal, mechanical and chemical equilibrium with its surroundings throughout. By this infinite, slow variation, the system is always almost close to equilibrium state.

Question 20.
Define specific heat capacity at constant pressure.
Answer:
Specific heat capacity at constant pressure $\left(s_{\mathrm{p}}\right.$ ): The amount of heat energy required to raise the temperature of one $\mathrm{kg}$ of a substance by $1 \mathrm{~K}$ or $1^{\circ} \mathrm{C}$ by keeping the pressure constant is called specific heat capacity of at constant pressure.
Question 21.
Define specific heat capacity at constant volume.
Answer:
Specific heat capacity at constant volume $\left.\mathrm{s}_{\mathrm{V}}\right)$ : The amount of heat energy required to raise the temperature of one $\mathrm{kg}$ of a substance by $1 \mathrm{~K}$ or $1^{\circ} \mathrm{C}$ by keeping the volume constant is called specific heat capacity at constant volume.
Question 22.
Define molar specific heat capacity at constant volume.
Answer:
The amount of heat required to rise the temperature of one mole of a substance by $1 \mathrm{~K}$ or $1{ }^{\circ} \mathrm{C}$ at constant volume is called molar specific heat capacity at constant volume.

Question 23.
Define molar specific heat capacity at constant pressure.
Answer:
The amount of heat required to rise the temperature of one mole of a substance by $1 \mathrm{~K}$ or $1^{\circ} \mathrm{C}$ at constant pressure is called molar specific heat capacity at constant pressure.
Question 24.
What is a isobaric process?
Answer:
It is a thermodynamic process which occurs at a constant pressure.
Question 25.
What is a isochoric process?
Answer:
It is a thermodynamic process which occurs at a constant volume.