Objective Physics for NEET

Abhay Kumar

Chapter 15

Calorimetry and Heat Transfer - all with Video Answers

Educators

+ 1 more educators

Chapter Questions

Problem 1

$5 \mathrm{gm}$ of steam at $100^{\circ} \mathrm{C}$ is passed into $6 \mathrm{gm}$ of ice at $0^{\circ} \mathrm{C}$. If the latent heats of steam and ice in cal per $\mathrm{gm}$ are 540 and 80 respectively, then the final temperature is
(a) $0^{\circ} \mathrm{C}$
(b) $100^{\circ} \mathrm{C}$
(c) $50^{\circ} \mathrm{C}$
(d) $30^{\circ} \mathrm{C}$

Akshaya Rs

Akshaya Rs

Numerade Educator

Problem 2

In Q.1, the mixture contains
(a) $11 \mathrm{gm}$ of water
(b) $8 \mathrm{gm}$ of water
(c) $6 \mathrm{gm}$ of water
(d) $5 \mathrm{gm}$ of water

Mahendra K

Numerade Educator

Problem 3

Three liquids with masses $m_{1}, m_{2}, m_{3}$ are thoroughly mixed. If their specific heats are $s_{1}, s_{2}, s_{3}$ and their temperatures $\theta_{1}, \theta_{2}, \theta_{3}$ respectively, then the temperature of the mixture is
(a) $\frac{s_{1} \theta_{1}+s_{2} \theta_{2}+s_{3} \theta_{3}}{m_{1} s_{1}+m_{2} s_{2}+m_{3} s_{3}}$
(b) $\frac{m_{1} s_{1} \theta_{1}+m_{2} s_{2} \theta_{2}+m_{3} s_{3} \theta_{3}}{m_{1} s_{1}+m_{2} s_{2}+m_{3} s_{3}}$
(c) $\frac{m_{1} s_{1} \theta_{1}+m_{2} s_{2} \theta_{2}+m_{3} s_{3} \theta_{3}}{m_{1} \theta_{1}+m_{2} \theta_{2}+m_{3} \theta_{3}}$
(d) $\frac{m_{1} \theta_{1}+m_{2} \theta_{2}+m_{3} \theta_{3}}{s_{1} \theta_{1}+s_{2} \theta_{2}+s_{3} \theta_{3}}$

Mahendra K

Numerade Educator

Problem 4

Three liquids of equal volumes are thoroughly mixed. If their specific heats are $s_{1}, s_{2}, s_{3}$ and their temperatures $\theta_{1}, \theta_{2}, \theta_{3}$ and their densities $d_{1}, d_{2}$ $d_{3}$ respectively, then the final temperature of the mixture is
(a) $\frac{s_{1} \theta_{1}+s_{2} \theta_{2}+s_{3} \theta_{3}}{d_{1} s_{1}+d_{2} s_{2}+d_{3} s_{3}}$
(b) $\frac{d_{1} s_{1} \theta_{1}+d_{2} s_{2} \theta_{2}+d_{3} s_{3} \theta_{3}}{d_{1} s_{1}+d_{2} s_{2}+d_{3} s_{3}}$
(c) $\frac{d_{1} s_{1} \theta_{1}+d_{2} s_{2} \theta_{2}+d_{3} s_{3} \theta_{3}}{d_{1} \theta_{1}+d_{2} \theta_{2}+d_{3} \theta_{3}}$
(d) $\frac{d_{1} \theta_{1}+d_{2} \theta_{2}+d_{3} \theta_{3}}{s_{1} \theta_{1}+s_{2} \theta_{2}+s_{3} \theta_{3}}$

Mahendra K

Numerade Educator

Problem 5

$250 \mathrm{gm}$ of water and equal volume of alcohol of mass $200 \mathrm{gm}$ are replaced successively in the same calorimeter and cool from $60^{\circ} \mathrm{C}$ to $55^{\circ} \mathrm{C}$ in 130 seconds and 67 seconds respectively. If the water equivalent of the calorimeter is $10 \mathrm{gm}$, then the specific heat of alcohol (in $\mathrm{cal} / \mathrm{gm}-{ }^{\circ} \mathrm{C}$ ) is
(a) $1.30$
(b) $0.67$
(c) $0.62$
(d) $0.985$

Mahendra K

Numerade Educator

Problem 6

A liquid of mass $m$ and specific heat $C$ is heated to a temperature $2 T$. Another liquid of mass $(m / 2)$ and specific heat $2 C$ is heated to a temperature $T$. If these two liquids are mixed, the resulting temperature of the mixture is
(a) $(2 / 3) T$
(b) $(8 / 5) T$
(c) $(3 / 5) T$
(d) $(3 / 2) T$

Pk

Pankaj Kumawat

Numerade Educator

Problem 7

$10 \mathrm{gm}$ of ice cubes at $0^{\circ} \mathrm{C}$ are released in a tumbler containing water (water equivalent $55 \mathrm{gm}$ ) at $40^{\circ} \mathrm{C}$. Assuming that negligible heat is taken from the surrounding the temperature of water in the tumbler becomes nearly $(L=80 \mathrm{cal} / \mathrm{gm})$
(a) $31^{\circ} \mathrm{C}$
(b) $22^{\circ} \mathrm{C}$
(c) $19^{\circ} \mathrm{C}$
(d) $15^{\circ} \mathrm{C}$

Akshaya Rs

Numerade Educator

Problem 8

The temperatures of equal masses of three different liquids $A, B$ and $C$ are $12^{\circ} \mathrm{C}, 19^{\circ} \mathrm{C}$ and $28^{\circ} \mathrm{C}$ respectively. The temperature when $A$ and $B$ are mixed is $16^{\circ} \mathrm{C}$, when $B$ and $C$ are mixed is $23^{\circ} \mathrm{C}$; what is the temperature when $A$ and $C$ are mixed?
(a) $31^{\circ} \mathrm{C}$
(b) $20.26^{\circ} \mathrm{C}$
(c) $19.5^{\circ} \mathrm{C}$
(d) $28^{\circ} \mathrm{C}$

Mahendra K

Numerade Educator

Problem 9

10 litres of a liquid with specific heat $0.2 \mathrm{cal} / \mathrm{gm}-{ }^{\circ} \mathrm{C}$ has the same thermal capacity as that of 20 litres of liquid with specific heat $0.3 \mathrm{cal} / \mathrm{gm}-{ }^{\circ} \mathrm{C}$, find the ratio of their densities
(a) $3: 1$
(b) $1: 3$
(c) $1: 6$
(d) $6: 1$

Mahendra K

Numerade Educator

Problem 10

A stationary object at $4^{\circ} \mathrm{C}$ and weighing $3.5 \mathrm{~kg}$ falls from a height of 2000 metres on a snow mountain at $0^{\circ} \mathrm{C}$. If the temperature of the object just before hitting the snow is $0^{\circ} \mathrm{C}$ and the object comes to rest immediately (Take $\left.g=10 \mathrm{~m} / \mathrm{s}^{2}\right)$ and latent heat of ice is $3.5 \times 10^{5} \mathrm{~J} / \mathrm{kg}$, then the object will melt
(a) $2 \mathrm{gm}$ of ice
(b) $20 \mathrm{gm}$ of ice
(c) $200 \mathrm{gm}$ of ice
(d) $2 \mathrm{~kg}$ of ice

Akshaya Rs

Numerade Educator

Problem 11

A test tube containing water is placed in boiling water so that its mouth remains outside the boiling water. Choose the wrong statement.
(a) Water in the test tube will soon begin to boil
(b) Temperature of water inside the tube will rise
(c) Convection currents will be set up in the water inside the tube
(d) Volume of water inside the tube will increase.

Mahendra K

Numerade Educator

Problem 12

A ball of thermal capacity $10 \mathrm{cal} /{ }^{\circ} \mathrm{C}$ is heated to the temperature of furnace. It is then transferred into a vessel containing water. The water equivalent of vessel and the contents is $200 \mathrm{gm}$. The temperature of the vessel and its contents rises from $10^{\circ} \mathrm{C}$ to $40^{\circ} \mathrm{C}$. What is the temperature of furnace?
(a) $640^{\circ} \mathrm{C}$
(b) $64^{\circ} \mathrm{C}$
(c) $600^{\circ} \mathrm{C}$
(d) $100^{\circ} \mathrm{C}$

Mahendra K

Numerade Educator

Problem 13

Two spheres $A$ and $B$ have diameters in the ratio $1: 2$, densities in the ratio $2: 1$ and specific heats in the ratio $1: 3$; find the ratio of their thermal capacities
(a) $1: 6$
(b) $1: 12$
(c) $1: 3$
(d) $1: 4$

Mahendra K

Numerade Educator

Problem 14

The ratio of radii of two spheres of same material is $1: 4$. Then, the ratio of their heat capacity will be
(a) $1 / 64$
(b) $1 / 32$
(c) $1 / 2$
(d) $1 / 4$

Mahendra K

Numerade Educator

Problem 15

What extinguishes a fire most quickly?
(a) Cold water
(b) Boiling water
(c) Hot water
(d) Ice

Mahendra K

Numerade Educator

Problem 16

A beaker contains $200 \mathrm{gm}$ of water. The heat capacity of the beaker is equal to that of $20 \mathrm{gm}$ of water. The initial temperature of water in the beaker is $20^{\circ} \mathrm{C}$. If $440 \mathrm{gm}$ of hot water at $92^{\circ} \mathrm{C}$ is poured in it, the final temperature, neglecting radiation loss, will be nearest to
(a) $58^{\circ} \mathrm{C}$
(b) $68^{\circ} \mathrm{C}$
(c) $73^{\circ} \mathrm{C}$
(d) $78^{\circ} \mathrm{C}$

Mahendra K

Numerade Educator

Problem 17

Two liquids $A$ and $B$ are at temperatures of $75^{\circ} \mathrm{C}$ and $15^{\circ} \mathrm{C}$. Their masses are in the ratio of $2: 3$ and their specific heats in the ratio $3: 4$. What is the resulting temperature?
(a) $90^{\circ} \mathrm{C}$
(b) $70^{\circ} \mathrm{C}$
(c) $35^{\circ} \mathrm{C}$
(d) $60^{\circ} \mathrm{C}$

Akshaya Rs

Numerade Educator

Problem 18

70 calories are required to raise the temperature of 2 moles of an ideal gas at constant pressure from $30^{\circ} \mathrm{C}$ to $35^{\circ} \mathrm{C}$. The amount of heat required (in calories) to raise the temperature of the same gas through the same range $\left(30^{\circ} \mathrm{C}\right.$ to $\left.35^{\circ} \mathrm{C}\right)$ at constant volume is
(a) 30
(b) 50
(c) 70
(d) 90

Mahendra K

Numerade Educator

Problem 19

In a pressure cooker, the cooking is fast, because
(a) the boiling point of water is raised by the increased pressure inside the cooker
(b) the boiling point of water is lowered by pressure
(c) more steam is available to cook the food at $100^{\circ} \mathrm{C}$
(d) more pressure is available to cook the food at $100^{\circ} \mathrm{C}$

Mahendra K

Numerade Educator

Problem 20

A steel ball of mass $m_{1}=1 \mathrm{~kg}$ moving with velocity $50 \mathrm{~m} / \mathrm{s}$ collides with another ball of mass $\mathrm{m}_{2}=200 \mathrm{gm}$ lying on the ground. During the collision their internal energies change equally and $T_{1}$ and $T_{2}$ are the rise in temperatures of masses $m_{1}$ and $m_{2}$ respectively. If specific heat of steel is $0.105$ and $J=4.18 \mathrm{~J} / \mathrm{cal}$, then
(a) $T_{1}=7.1{ }^{\circ} \mathrm{C}$ and $T_{2}=1.47^{\circ} \mathrm{C}$
(b) $T_{1}=1.47^{\circ} \mathrm{C}$ and $T_{2}=7.1^{\circ} \mathrm{C}$
(c) $T_{1}=3.4 \mathrm{~K}$ and $T_{2}=17.0 \mathrm{~K}$
(d) $T_{1}=7.1 \mathrm{~K}$ and $T_{2}=1.4 \mathrm{~K}$

Mahendra K

Numerade Educator

Problem 21

A lead ball moving with velocity $v$ strikes a wall and stops. If $50 \%$ of its energy is converted into heat, then what will be the increase in temperature? (Specific heat of lead is $s$ )
(a) $\frac{2 v^{2}}{J s}$
(b) $\frac{v^{2}}{4 J s}$
(c) $\frac{v^{2} s}{J}$
(d) $\frac{v^{2} s}{2 J}$

Mahendra K

Numerade Educator

Problem 22

Heat required to melt $1 \mathrm{gm}$ of ice is 80 cal. A man melts $60 \mathrm{gm}$ of ice by chewing in one minute. His power is
(a) $4800 \mathrm{~W}$
(b) $336 \mathrm{~W}$
(c) $1.33 \mathrm{~W}$
(d) $0.75 \mathrm{~W}$

Akshaya Rs

Numerade Educator

Problem 23

If mass-energy equivalence is taken into account, when water is cooled to form ice, the mass of water should be
(a) increase
(b) remain unchanged
(c) decrease
(d) first increase then decrease

Akshaya Rs

Numerade Educator

Problem 24

It takes 15 minutes to raise a certain amount of water from $0^{\circ} \mathrm{C}$ to the boiling point using a heater. Then, it takes 1 hour and 20 minutes more to convert all the water into vapour. Then, the latent heat of vaporisation of water is
(a) $545 \mathrm{cal}$
(b) $540 \mathrm{cal}$
(c) $533 \mathrm{cal}$
(d) $513 \mathrm{cal}$

Akshaya Rs

Numerade Educator

Problem 25

A body of specific heat $0.2 \mathrm{kcal} / \mathrm{kg}^{\circ} \mathrm{C}$ is heated through $100^{\circ} \mathrm{C}$. the percentage increase in its mass is
(a) $9 \%$
(b) $9.3 \times 10^{-11 \%}$
(c) $10 \%$
(d) none of these

Akshaya Rs

Numerade Educator

Problem 26

An electrically heated coil is immersed in a calorimeter containing $360 \mathrm{gm}$ of water at $10^{\circ} \mathrm{C}$. The coil consumes energy at the rate of 90 watts. The water equivalent of calorimeter and coil is $40 \mathrm{gm}$. The temperature of water after 10 minutes is
(a) $4.214^{\circ} \mathrm{C}$
(b) $42.14^{\circ} \mathrm{C}$
(c) $30^{\circ}$
(d) none of these

Mahendra K

Numerade Educator

Problem 27

A metal sphere of radius $r$ and specific heat $S$ is rotated about an axis passing through its centre at a speed of $n$ rotations per second. It is suddenly stopped and $50 \%$ of its energy is used in increasing its temperature. Then, the rise in temperature of the sphere is
(a) $\frac{2 \pi^{2} n^{2} r^{2}}{5 S}$
(b) $\frac{\pi^{2} n^{2}}{10 r^{2} S}$
(c) $\frac{7}{8} \pi r^{2} n^{2} S$
(d) $\frac{5(\pi r n)^{2}}{14 S}$

Mahendra K

Numerade Educator

Problem 28

A steel ball of mass $0.1 \mathrm{~kg}$ falls freely from a height of $10 \mathrm{~m}$ and bounces to a height of $5.4 \mathrm{~m}$ from the ground. If the dissipated energy in this process is absorbed by the ball, the rise in its temperature is: (Specific heat of steel $=460 \mathrm{~J} /$ $\left.\mathrm{kg} /{ }^{\circ} \mathrm{C}, g=10 \mathrm{~m} \mathrm{~s}^{-2}\right)$
(a) $0.01^{\circ} \mathrm{C}$
(b) $0.1^{\circ} \mathrm{C}$
(c) $1^{\circ} \mathrm{C}$
(d) $1.1^{\circ} \mathrm{C}$

Mahendra K

Numerade Educator

Problem 29

The specific heat of many solids at low temperatures varies with absolute temperature $T$ according to the relation $S=a T^{3}$, where $a$ is a constant. The heat energy required to raise the temperature of a mass $m$ of such a solid from $T=0 \mathrm{~K}$ to $T=20 \mathrm{~K}$ is
(a) $4 \times 10^{4} \mathrm{~mA}$
(b) $2 \times 10^{3} \mathrm{~mA}$
(c) $8 \times 10^{6} \mathrm{~mA}$
(d) $2 \times 10^{6} \mathrm{~mA}$

Mahendra K

Numerade Educator

Problem 30

Critical temperature can be defined as the
(a) temperature at which there is no motion between the molecules
(b) temperature at which a gas is converted into its liquid state
(c) temperature at which volume of a gas becomes zero
(d) temperature above which a gas cannot be liquefied no matter however high the pressure may be

Mahendra K

Numerade Educator

Problem 31

The quantity of heat which crosses unit area of a metal plate during conduction depends upon
(a) the density of the metal
(b) the temperature gradient perpendicular to the area
(c) the temperature to which metal is heated
(d) the area of the metal plate

Akshaya Rs

Numerade Educator

Problem 32

Which of the following combinations of properties would be most desirable for a cooking pot?
(a) High specific heat and low thermal conductivity
(b) Low specific heat and high thermal conductivity
(c) High specific heat and high thermal conductivity
(d) Low specific heat and low thermal conductivity

Mahendra K

Numerade Educator

Problem 33

A bullet of mass $10 \times 10^{-3} \mathrm{~kg}$ moving with a speed of $20 \mathrm{~ms}^{-1}$ hits an ice block $\left(0^{\circ} \mathrm{C}\right)$ of $990 \mathrm{~g}$ kept at rest on a frictionless floor and gets embedded in it. If ice takes $50 \%$ of KE lost by the system, the amount of ice melted (in grams) approximately is: $(J=4.2 \mathrm{~J} / \mathrm{cal} ;$ latent heat of ice $=80 \mathrm{cal} / \mathrm{g}$ )
(a) 6
(b) 3
(c) $6 \times 10^{-3}$
(d) $3 \times 10^{-3}$

Mahendra K

Numerade Educator

Problem 34

Liquid oxygen at $50 \mathrm{~K}$ is heated to $300 \mathrm{~K}$ at constant pressure of 1 atm. The rate of heating is constant. Which of the following graphs represents the variation of temperature with time?
(a)
(b)
(c)
(d)

Mahendra K

Numerade Educator

Problem 35

Under steady state the temperature of a body
(a) increases with time
(b) decreases with time
(c) does not change with time and is same at all points of the body
(d) does not change with time but is different at different cross-section of the body

Mahendra K

Numerade Educator

Problem 36

A block of ice at $-10^{\circ} \mathrm{C}$ is slowly heated and converted to steam at $100^{\circ} \mathrm{C} .$ Which of the following curves represents this phenomenon qualitatively?
(a)
(b)
Heat supplied
(c)
(d)

Akshaya Rs

Numerade Educator

Problem 37

The following figure represents the temperature versus time plot for a given amount of a substance when heat energy is supplied to it at a fixed rate and at a constant pressure. Which part of the above plot represent a phase change?
(a) $a$ to $b$ and $e$ to $f$
(b) $b$ to $c$ and $c$ to $d$
(c) $d$ to $e$ and $e$ to $f$
(d) $b$ to $c$ and $d$ to $e$

Akshaya Rs

Numerade Educator

Problem 38

If $K$ and $\sigma$ respectively are the thermal and electrical conductivities of a metal at absolute temperature $T$, then
(a) $\frac{K}{\sigma T}=$ constant
(b) $\frac{K}{\sigma}=$ constant
(c) $\frac{K}{T}=$ constant
(d) $\frac{\sigma}{K T}=$ constant

Akshaya Rs

Numerade Educator

Problem 39

$310 \mathrm{~J}$ of heat is required to raise the temperature of 2 mole of an ideal gas at constant pressure from $25^{\circ} \mathrm{C}$ to $35^{\circ} \mathrm{C}$. The amount of heat required to raise the temperature of the gas through the same range at constant volume is
(a) $384 \mathrm{~J}$
(b) $144 \mathrm{~J}$
(c) $276 \mathrm{~J}$
(d) $452 \mathrm{~J}$

Mahendra K

Numerade Educator

Problem 40

According to Ingen-Hauz's experiment the thermal conductivity $K$ and length $L$ of the metal rod upto which the wax melts are related as
(a) $\frac{K}{L}=$ constant
(b) $\frac{K^{2}}{L}=$ constant
(c) $\frac{K}{L^{2}}=$ constant
(d) $K L=$ constant

Akshaya Rs

Numerade Educator

Problem 41

Two identical plates of metal are welded end to end as shown in figure (A); 20 cal of heat flows through it in 4 minutes. If the plates are welded as shown in figure (B), the same amount of heat will flow through the plates in:
(a) 1 minute
(b) 2 minutes
(c) 4 minutes
(d) 16 minutes

Mahendra K

Numerade Educator

Problem 42

Two plates of same thickness, of coefficients of thermal conductivities $K_{1}$ and $K_{2}$ and areas of crosssection $A$ and $A_{2}$, are connected as shown; the common coefficient of thermal conductivity $K$ will be
(a) $K_{1} A_{1}+K_{2} A_{2}$
(b) $\frac{K_{1} A_{1}+K_{2} A_{2}}{A_{1}+A_{2}}$
(c) $\frac{K_{1} A_{2}+K_{2} A_{1}}{A_{1}+A_{2}}$
(d) $\frac{K_{1} A_{1}}{K_{2} A_{2}}$

Mahendra K

Numerade Educator

Problem 43

One end of a metal rod of length $1.0 \mathrm{~m}$ and area of cross-section $100 \mathrm{~cm}^{2}$ is maintained at $100^{\circ} \mathrm{C}$. If the other end of the rod is maintained at $0^{\circ} \mathrm{C}$, the quantity of heat transmitted through the rod per minute is; (Coefficient of thermal conductivity of material of the rod $=100 \mathrm{~W} / \mathrm{kg} / \mathrm{K}$ )
(a) $3 \times 10^{3} \mathrm{~J}$
(b) $6 \times 10^{3} \mathrm{~J}$
(c) $9 \times 10^{3} \mathrm{~J}$
(d) $12 \times 10^{3} \mathrm{~J}$

Akshaya Rs

Numerade Educator

Problem 44

In a composite rod, when two rods of different lengths and of the same area of cross-section are joined end to end, then if $K$ is the effective coefficient of thermal conductivity, $\frac{l_{1}+l_{2}}{K}$ is equal to:
(a) $\frac{l_{1}}{K_{1}}-\frac{l_{2}}{K_{2}}$
(b) $\frac{l_{1}}{K_{2}}-\frac{l_{2}}{K_{1}}$
(c) $\frac{l_{1}}{K_{1}}+\frac{l_{2}}{K_{2}}$
(d) $\frac{l_{1}}{K_{2}}+\frac{l_{2}}{K_{1}}$

Mahendra K

Numerade Educator

Problem 45

A piece of glass is heated to a high temperature and then allowed to cool. If it cracks, a probable reason for this is the following property of glass:
(a) low thermal conductivity
(b) high thermal conductivity
(c) high specific heat
(d) high melting point

Akshaya Rs

Numerade Educator

Problem 46

A cylinder of radius $R$ made of a material of thermal conductivity $K_{1}$ is surrounded by a cylindrical shell of inner radius $R$ and outer radius $2 R$ made of a material of thermal conductivity $K_{2}$. The two ends of the combined system are maintained at two different temperatures. There is no loss of heat across the cylindrical surface and the system is in steady state. The effective thermal conductivity of the system is:
(a) $K_{1}+K_{2}$
(b) $\frac{K_{1}+3 K_{2}}{4}$
(c) $\frac{K_{1} K_{2}}{K_{1}+K_{2}}$
(d) $\frac{3 K_{1}+K_{2}}{4}$

Mahendra K

Numerade Educator

Problem 47

Two walls of thicknesses $d$, and $d_{2}$ and thermal conductivities $K_{1}$ and $K_{2}$ are in contact. In the steady state, if the temperatures at the outer surface are $T_{1}$ and $T_{2}$, the temperature at the common wall is:
(a) $\left(K_{1} T_{1} d_{2}+K_{2} T_{2} d_{1}\right) /\left(K_{1} d_{2}+K_{2} d_{1}\right)$
(b) $\left(K_{1} T_{1}+K_{2} T_{2}\right) /\left(d_{1}+d_{2}\right)$
(c) $\left(\frac{K_{1} d_{1}+K_{2} d_{2}}{T_{1}+T_{2}}\right)$
(d) $\left(K_{1} T_{1} d_{1}+K_{2} T_{2} d_{2}\right) /\left(K_{1} d_{1}+K_{2} d_{2}\right)$

Mahendra K

Numerade Educator

Problem 48

The temperature of the two outer surfaces of a composite slab, consisting of two materials having coefficients of thermal conductivity $K$ and $2 K$ and thickness $x$ and $4 x$ respectively are $T_{2}$ and $T_{1}\left(T_{2}>T_{1}\right)$. The rate of heat transfer through the slab, in a steady state is $\left(\frac{A\left(T_{2}-T_{1}\right) K}{x}\right) f$, with
fequal to:
(a) $]$
(b) $1 / 2$
(c) $2 / 3$
(d) $1 / 3$

Mahendra K

Numerade Educator

Problem 49

Two vessels of different materials are similar in size in every respect. The same quantity of ice filled in them gets melted in 20 minutes and 40 minutes respectively. The ratio of thermal conductivities of the metals is:
(a) $5: 6$
(b) $6: 5$
(c) $3: 1$
(d) $2: 1$

Mahendra K

Numerade Educator

Problem 50

Three rods of material $X$ and three rods of material $Y$ are connected as shown in figure. All are identical in length and cross-sectional area. if end $A$ is maintained at $60^{\circ} \mathrm{C}$, end $E$ at $10^{\circ} \mathrm{C}$, thermal conductivity of $X$ is $0.92 \mathrm{cal} / \mathrm{sec}-\mathrm{cm}-{ }^{\circ} \mathrm{C}$ and that of $Y$ is $0.46 \mathrm{cal} / \mathrm{sec}-\mathrm{cm}-{ }^{\circ} \mathrm{C}$
them find the temperature of junctions $B, C, D:$
(a) $20^{\circ} \mathrm{C}, 30^{\circ} \mathrm{C}, 20^{\circ} \mathrm{C}$
(b) $30^{\circ} \mathrm{C}, 20^{\circ}, 20^{\circ} \mathrm{C}$
(c) $20^{\circ} \mathrm{C}, 20^{\circ} \mathrm{C}, 30^{\circ} \mathrm{C}$
(d) $20^{\circ} \mathrm{C}, 20^{\circ} \mathrm{C}, 20^{\circ} \mathrm{C}$

Mahendra K

Numerade Educator

Problem 51

Three rods made of the same material and having the same cross-section have been joined as shown in the figure. Fach rod is of the same length. The left and right ends are kept at $0^{\circ} \mathrm{C}$ and $90^{\circ} \mathrm{C}$ respectively. The temperature of the junction of the three rods will be
(a) $45^{\circ} \mathrm{C}$
(b) $60^{\circ} \mathrm{C}$
(c) $30^{\circ} \mathrm{C}$
(d) $20^{\circ} \mathrm{C}$

Akshaya Rs

Numerade Educator

Problem 52

Five rods of same dimensions are arranged as shown in figure. They have thermal conductivities $K_{1}, K_{2}$, $K_{3}, K_{4}$ and $K_{5}$ when points $A$ and $B$ are maintained at different temperature. No heat flows through the central rod if
(a) $K_{1} K_{4}=K_{2} K_{3}$
(b) $K_{1}=K_{4}$ and $K_{2}=K_{3}$
(c) $\frac{K_{1}}{K_{4}}=\frac{K_{2}}{K_{3}}$
(d) $K_{1} K_{2}=K_{3} K_{4}$

Akshaya Rs

Numerade Educator

Problem 53

Two ends of a conducting rod of varying cross-section are maintained at $200^{\circ} \mathrm{C}$ and $0^{\circ} \mathrm{C}$ respectively. In steady state
(a) temperature differences across $A B$ and $C D$ are equal
(b) temperature difference across $A B$ is greater than that across $C D$
(c) temperature difference across $A B$ is less than that across $C D$
(d) temperature difference may be equal or different depending upon thermal conductivity of the rod

Mahendra K

Numerade Educator

Problem 54

Six identical conducting rods are joined as shown in figure.

Points $A$ and $D$ are maintained at temperatures $200^{\circ} \mathrm{C}$ and $20^{\circ} \mathrm{C}$ respectively. The temperature of junction $B$ will be
(a) $120^{\circ} \mathrm{C}$
(b) $100^{\circ} \mathrm{C}$
(c) $140^{\circ} \mathrm{C}$
(d) $80^{\circ} \mathrm{C}$

Akshaya Rs

Numerade Educator

Problem 55

Three rods of identical corss-sectional area and made from the same metal form the sides of an isosceles triangle $A B C$ right angled at $B$. The points $A$ and $B$ are maintained at temperatures $T$ an $\sqrt{2} T$ respectively in the steady state. Assuming that only heat conduction takes place, temperature of point $C$ will be
(a) $\frac{3 T}{\sqrt{2}+1}$
(b) $\frac{T}{\sqrt{2}+1}$
(c) $\frac{T}{\sqrt{3}(\sqrt{2}-1)}$
(d) $\frac{T}{\sqrt{2}-1}$

Mahendra K

Numerade Educator

Problem 56

If the temperature difference on the two sides of a wall increases from $100^{\circ} \mathrm{C}$ to $200^{\circ} \mathrm{C}$, its thermal conductivity
(a) remains unchanged
(b) is doubled
(c) is halved
(d) becomes four times

Akshaya Rs

Numerade Educator

Problem 57

The ratio of the coefficient of thermal conductivity of two different materials is $5: 3$. If the thermal resistance of the rods of same thickness of these materials is same, then the ratio of the length of these rods will be
(a) $3: 5$
(b) $5: 3$
(c) $3: 4$
(d) $3: 2$

Akshaya Rs

Numerade Educator

Problem 58

A body cools from $60^{\circ} \mathrm{C}$ to $50^{\circ} \mathrm{C}$ in 10 minutes. If the room to hold good, the temperature of the body at the end of the next 10 minutes will be
(a) $38.5^{\circ} \mathrm{C}$
(b) $40^{\circ} \mathrm{C}$
(c) $42.85^{\circ} \mathrm{C}$
(d) $45^{\circ} \mathrm{C}$

Mahendra K

Numerade Educator

Problem 59

If the temperature of a hot body is raised by $5 \%$, then the heat energy radiated would increase by
(a) $5 \%$
(b) $10 \%$
(c) $11.65 \%$
(d) $21.55 \%$

Mahendra K

Numerade Educator

Problem 60

A thermos flask is polished well
(a) to make is attractive
(b) for shining
(c) to absorb all radiations from outside
(d) to reflect all radiations from outside

Mahendra K

Numerade Educator

Problem 61

If a liquid is heated in weightlessness, the heat is transmitted through
(a) conduction
(b) convection
(c) radiation
(d) neither, because the liquid cannot be heated in weightlessness

Mahendra K

Numerade Educator

Problem 62

A sphere, a cube and a disc all of the same material, quality and volume are heated to $600^{\circ} \mathrm{C}$ and left in air. Which of these will have the lowest rate of cooling ?
(a) Sphere
(b) Cube
(c) Disc
(d) All will have same rate

Mahendra K

Numerade Educator

Problem 63

A surface at temperature $T_{0} \mathrm{~K}$ receives power $P$ by radiation from a small sphere at temperature $T>T_{n}$ and at a distance $d .$ If both $T$ and $d$ are doubled, the power received by surface will become approximately
(a) $P$
(b) $2 P$
(c) $4 P$
(d) $16 P$

Mahendra K

Numerade Educator

Problem 64

We find that the temperature of air decreases as one goes up from the earth's surface because
(a) the atmospheric pressure drops with height
(b) the earth which radiates in the infrared region is the main heat source and temperature drops as we go away from it
(c) the density of air drops with height and the air therefore cannot hold stronger as we go up
(d) winds are stronger as we go up

Mahendra K

Numerade Educator

Problem 65

Two stars $P$ and $Q$ are observed at night. $\operatorname{Star} P$ appears reddish while star $Q$ as white. From this, we conclude
(a) temperature of $Q$ is higher than that of $P$
(b) temperature of $Q$ is lower than that of $P$
(c) $\operatorname{star} Q$ is at same distance as that of $\operatorname{star} P$
(d) $\operatorname{star} P$ is farther away than $\operatorname{star} Q$

Akshaya Rs

Numerade Educator

Problem 66

A solid sphere and a hollow sphere of same material and size are heated to same temperature and allowed to cool in the same surroundings. If the temperature difference between each sphere and its surroundings is $T$, then
(a) the hollow sphere will cool at a faster rate for all values of $T$
(b) the solid sphere will cool at a faster rate for all values of $T$
(c) both spheres will cool at the same rate for all values of $T$
(d) both spheres will cool at the same rate only for small values of $T$

Mahendra K

Numerade Educator

Problem 67

For most practical temperature, we may take it that all bodies radiate heat in proportion to the fourth power of temperature $T$. If a body (coated black) at $400 \mathrm{~K}$ surrounded by atmosphere at $300 \mathrm{~K}$ has cooling rate $r_{o}$, the same body at $900 \mathrm{~K}$, surrounded by the same atmosphere, will have cooling rate closer to
(a) $16 r / 3$
(b) $81 r_{o} / 16$
(c) $16 r$
(d) $4 r_{\text {o }}$

Akshaya Rs

Numerade Educator

Problem 68

For a perfectly black body the energy radiated per unit time per unit area is directly proportional to
(a) the absolute temperature
(b) the square of absolute temperature
(c) the cube of absolute temperature
(d) the fourth power of absolute temperature

Akshaya Rs

Numerade Educator

Problem 69

Mud houses are cooler in summer and warmer in winter because
(a) mud is a bad conductor of heat
(b) mud is superconductor of heat
(c) mud is good conductor of heat
(d) none of the above

Akshaya Rs

Numerade Educator

Problem 70

A blue glass when heated will glow with
(a) red colour
(b) blue colour
(c) white light
(d) yellow colour

Mahendra K

Numerade Educator

Problem 71

It is seen that in proper ventilation of a building, windows must be open near the bottom and the top of the walls so as to let pass
(a) in hot air near the roof and cool air out near the bottom
(b) out hot air near the roof
(c) in cool air near the bottom and hot air out near the roof
(d) in more air

Supratim Pal

Numerade Educator

Problem 72

Which principle fully explains the spectrum of radiation?
(a) Rayleigh-Jeans principle
(b) Planck's principle
(c) Wien's principle
(d) Stefan's principle

Saman Zulfiqar

Numerade Educator

Problem 73

In a closed room, heat transfer takes place by
(a) conduction
(b) convection
(c) radiation
(d) all of these

Akshaya Rs

Numerade Educator

Problem 74

A heated piece of green glass seen in darkness will
(a) appear white
(b) appear red
(c) appear green
(d) not be visible

Akshaya Rs

Numerade Educator

Problem 75

An ideal black body at room temperature is thrown into a furnace. It is observed that:
(a) it is the darkest body at all times
(b) it cannot be distinguished at all times
(c) initially it is the darkest body and later it becomes
(d) initially it is the darkest body and later it cannot be distinguished

Akshaya Rs

Numerade Educator

Problem 76

Two circular discs $A$ and $B$ with equal radii are blackened. They are heated to same temperature and are cooled under identical conditions. What inference do you draw from their cooling curves?
(a) $A$ and $B$ have same specific heats
(b) Specific heat of $A$ is less
(c) Specific heat of $B$ is less
(d) Nothing can be said

Supratim Pal

Numerade Educator

Problem 77

Three objects coloured black, grey and white can withstand hostile conditions upto $2800^{\circ} \mathrm{C}$. These objects are thrown into a furnace where each of them attains a temperature of $2000^{\circ} \mathrm{C}$. Which object will glow the brightest?
(a) The white object
(b) The black object
(c) All glow with equal brightness
(d) Grey object

Supratim Pal

Numerade Educator

Problem 78

A body has same temperature as that of the surround. ings. Then:
(a) it radiates same heat as it absorbs
(b) it absorbs more, radiates less heat
(c) it radiates more, absorbs less heat
(d) it never radiates heat

Akshaya Rs

Numerade Educator

Problem 79

The temperature of the sun can be measured by:
(a) Planck's law
(b) Kirchoff's law
(c) Stefan-Boltzmann law
(d) Wien's displacement law

Akshaya Rs

Numerade Educator

Problem 80

In which of the following heat loss is primarily not due to convection?
(a) Boiling of water
(b) Land and sea breeze
(c) Heating of glass surface of a bulb due to current in filament
(d) Circulation of air around blast furnace

Supratim Pal

Numerade Educator

Problem 81

Flash light equipped with a new set of batteries, produces bright white light. As the batteries wear out :
(a) the light intensity gets reduced with no change in its colour
(b) light colour changes first to yellow and then red with no change in intensity
(c) it stops working suddenly while giving white light
(d) colour changes to red and also intensity gets reduced

Supratim Pal

Numerade Educator

Problem 82

A piece of blue glass heated to a high temperature and a piece of red glass at room temperature, are taken inside a dimly lit room, then:
(a) the blue piece will look blue and red will look as usual
(b) red look brighter and blue look ordinary blue
(c) blue shines like brighter red compared to the red piece
(d) both the pieces will look equally red

Supratim Pal

Numerade Educator

Problem 83

If the amount of heat energy received per unit area from the sun is measured on the earth, mars and jupiter, it will be:
(a) same for all
(b) in decreasing order jupiter, mars and the earth
(c) in increasing order jupiter, mars and the earth
(d) in decreasing order mars, the earth and jupiter

Akshaya Rs

Numerade Educator

Problem 84

Two friends $A$ and $B$ are waiting for another friend for tea. $A$ took the tea in a cap and mixed the cold milk and then waits. $B$ took the tea in the cup and then mixed the cold milk when the friend comes. Then the tea will be hotter in the cup of:
(a) $\underline{A}$
(b) $\underline{B}$
(c) tea will be equally hot in both cups
(d) friend's cup

Pritesh Ranjan

Numerade Educator