Heat Transfer & Newton’s Law of Cooling Practice Questions - DPP for NEET

 Page 1


DIRECTIONS (Q.1-Q.21) : There are 21 multiple choice
questions. Each question has 4 choices (a), (b), (c) and (d), out
of which ONLY ONE choice is correct.
Q.1 Two rods (one semi-circular and other straight) of same
material and of same cross-sectional area are joined as
shown in the figure. The points A and B are maintained at
different temperature. The ratio of the heat transferred
through a cross-section of a semi-circular rod to the heat
transferred through a cross section of the straight rod in a
given time is
(a) 2 : p
(b) 1 : 2
A B
Straight rod
S
emi
 circular ro
d
(c) p : 2
(d) 3 : 2
Q.2 A wall is made up of two layers A and B. The thickness of
the two layers is the same, but materials are different. The
thermal conductivity of A is double than that of B. In thermal
equilibrium the temperature difference between the two
ends is 36°C. Then the difference of temperature at the
two surfaces of A will be
(a) 6°C (b) 12°C (c) 18°C (d) 24°C
Q.3 A room is maintained at 20°C by a heater of resistance 20
ohm connected to 200 volt mains. The temperature is
uniform through out the room and heat is transmitted
through a glass window of area 1m
2
 and thickness 0.2 cm.
What will be the temperature outside? Given that thermal
conductivity K for glass is 0.2 cal/m/°C/sec and J = 4.2 J/
cal
(a) 15.24°C (b) 15.00°C
(c) 24.15°C (d) None of these
Page 2


DIRECTIONS (Q.1-Q.21) : There are 21 multiple choice
questions. Each question has 4 choices (a), (b), (c) and (d), out
of which ONLY ONE choice is correct.
Q.1 Two rods (one semi-circular and other straight) of same
material and of same cross-sectional area are joined as
shown in the figure. The points A and B are maintained at
different temperature. The ratio of the heat transferred
through a cross-section of a semi-circular rod to the heat
transferred through a cross section of the straight rod in a
given time is
(a) 2 : p
(b) 1 : 2
A B
Straight rod
S
emi
 circular ro
d
(c) p : 2
(d) 3 : 2
Q.2 A wall is made up of two layers A and B. The thickness of
the two layers is the same, but materials are different. The
thermal conductivity of A is double than that of B. In thermal
equilibrium the temperature difference between the two
ends is 36°C. Then the difference of temperature at the
two surfaces of A will be
(a) 6°C (b) 12°C (c) 18°C (d) 24°C
Q.3 A room is maintained at 20°C by a heater of resistance 20
ohm connected to 200 volt mains. The temperature is
uniform through out the room and heat is transmitted
through a glass window of area 1m
2
 and thickness 0.2 cm.
What will be the temperature outside? Given that thermal
conductivity K for glass is 0.2 cal/m/°C/sec and J = 4.2 J/
cal
(a) 15.24°C (b) 15.00°C
(c) 24.15°C (d) None of these
2
DPP/ P 23
Q.4 A composite metal bar of uniform section is made up of
length 25 cm of copper, 10 cm of nickel and 15 cm of
aluminium. Each part being in perfect thermal contact with
the adjoining part. The copper end of the composite rod is
maintained at 100°C and the aluminium end at 0°C. The
whole rod is covered with belt so that there is no heat loss
occurs at the sides. If K
Cu
 =  2K
Al
 and K
Al
 = 3K
Ni
, then
what will be the temperatures of Cu – Ni and Ni – Al
junctions respectively
Cu Ni Al
100° C 0° C
(a) 23.33°C and 78.8°C (b) 83.33°C and 20°C
(c) 50°C a nd 30°C (d) 30°C a nd 50°C
Q.5 Three rods of the same dimension have thermal
conductivities 3K, 2K and K. They are arranged as shown
in fig. with their ends at 100°C, 50°C and 20°C. The
temperature of their junction is
(a) 60°C
(b) 70°C
(c) 50°C
100°C
50°C
20°C
K
2K
3K
(d) 35°C
Q.6 A black body is at a temperature of 2880 K. The energy of
radiation emitted by this object with wavelength between
499 nm and 500 nm is U
1
, between 999 nm and 1000 nm
is U
2
 and between 1499 nm and 1500 nm is U
3
. The W ein's
constant b = 2.88 × 10
6
 nm K. Then
(a) U
1 
= 0 (b) U
3 
= 0 (c) U
1 
> U
2
(d) U
2 
> U
1
Q.7 A body initially at 80° C cools to 64° C in 5 minutes and
to 52° C in 10 minutes. The temperature of the body after
15 minutes will be
(a) 42.7° C (b) 35° C (c) 47° (d) 40° C
Q.8 A 5 cm thick ice block is there on the surface of water in a
lake. The temperature of air is – 10° C; how much time it
will take to double the thickness of the block
(L = 80 cal/g, K
ice
 = 0.004 erg/s-k, d
ice
 = 0.92 g cm
–3
)
(a) 1 hour (b) 191 hours
. (c) 19.1 hours (d) 1.91 hours
Q.9 A cylindrical rod with one end in a steam chamber and the
other end in ice results in melting of 0.1 gm of ice per
second. If the rod is replaced by another with half the length
and double the radius of the first and if the thermal
conductivity of material of second rod is 
1
4
 that of first,
the rate at which ice melts in gm/sec will be
(a) 3.2 (b) 1.6 (c) 0.2 (d) 0.1
Q.10 An ice box used for keeping eatable cold has a total wall
area of 1 metre
2
 and a wall thickness of 5.0 cm. The thermal
conductivity of the ice box is K = 0.01 joule/metre °C. It
is filled with ice at 0° C along with eatables on a day when
the temperature is 30°C. The latent heat of fusion of ice is
334 × 10
3
 joules/kg. The amount of ice melted in one day
is  (1 day =  86,400 seconds)
(a) 776 gm (b) 7760 gm
(c) 11520 gm (d) 1552 gm
Q.11 A solid copper sphere (density r and specific heat capacity
c) of radius r at an initial temperature 200 K is suspended
inside a chamber whose walls are at almost 0 K. The time
required (in µ s) for the temperature of the sphere to drop
to 100 K is
(a)
72
7
rc r
s
(b)
7
72
rc r
s
(c)
27
7
rc r
s
(d)
7
27
rc r
s
Q.12 Four rods of identical cross-sectional area and made from
the same metal form the sides of square. The temperature
of two diagonally opposite points  are T and 2T
respectively in the steady state. Assuming that only heat
conduction takes place, what will be the temperature
difference between other two points
(a)
21
2
T
+
(b)
2
21
T
+
(c)0 (d) None of these
Q.13 Consider two hot bodies B
1
 and B
2 
which have temperature
100° C  and 80° C respectively at t = 0. The temperature
of surroundings is 40° C. The ratio of the respective rates
of cooling R
1
 and R
2
 of these two bodies at t = 0 will be
(a) R
1
 : R
2
 = 3 : 2 (b) R
1
 : R
2
 = 5 : 4
(c) R
1
 : R
2
 = 2 : 3 (d) R
1
 : R
2
 = 4 : 5
Page 3


DIRECTIONS (Q.1-Q.21) : There are 21 multiple choice
questions. Each question has 4 choices (a), (b), (c) and (d), out
of which ONLY ONE choice is correct.
Q.1 Two rods (one semi-circular and other straight) of same
material and of same cross-sectional area are joined as
shown in the figure. The points A and B are maintained at
different temperature. The ratio of the heat transferred
through a cross-section of a semi-circular rod to the heat
transferred through a cross section of the straight rod in a
given time is
(a) 2 : p
(b) 1 : 2
A B
Straight rod
S
emi
 circular ro
d
(c) p : 2
(d) 3 : 2
Q.2 A wall is made up of two layers A and B. The thickness of
the two layers is the same, but materials are different. The
thermal conductivity of A is double than that of B. In thermal
equilibrium the temperature difference between the two
ends is 36°C. Then the difference of temperature at the
two surfaces of A will be
(a) 6°C (b) 12°C (c) 18°C (d) 24°C
Q.3 A room is maintained at 20°C by a heater of resistance 20
ohm connected to 200 volt mains. The temperature is
uniform through out the room and heat is transmitted
through a glass window of area 1m
2
 and thickness 0.2 cm.
What will be the temperature outside? Given that thermal
conductivity K for glass is 0.2 cal/m/°C/sec and J = 4.2 J/
cal
(a) 15.24°C (b) 15.00°C
(c) 24.15°C (d) None of these
2
DPP/ P 23
Q.4 A composite metal bar of uniform section is made up of
length 25 cm of copper, 10 cm of nickel and 15 cm of
aluminium. Each part being in perfect thermal contact with
the adjoining part. The copper end of the composite rod is
maintained at 100°C and the aluminium end at 0°C. The
whole rod is covered with belt so that there is no heat loss
occurs at the sides. If K
Cu
 =  2K
Al
 and K
Al
 = 3K
Ni
, then
what will be the temperatures of Cu – Ni and Ni – Al
junctions respectively
Cu Ni Al
100° C 0° C
(a) 23.33°C and 78.8°C (b) 83.33°C and 20°C
(c) 50°C a nd 30°C (d) 30°C a nd 50°C
Q.5 Three rods of the same dimension have thermal
conductivities 3K, 2K and K. They are arranged as shown
in fig. with their ends at 100°C, 50°C and 20°C. The
temperature of their junction is
(a) 60°C
(b) 70°C
(c) 50°C
100°C
50°C
20°C
K
2K
3K
(d) 35°C
Q.6 A black body is at a temperature of 2880 K. The energy of
radiation emitted by this object with wavelength between
499 nm and 500 nm is U
1
, between 999 nm and 1000 nm
is U
2
 and between 1499 nm and 1500 nm is U
3
. The W ein's
constant b = 2.88 × 10
6
 nm K. Then
(a) U
1 
= 0 (b) U
3 
= 0 (c) U
1 
> U
2
(d) U
2 
> U
1
Q.7 A body initially at 80° C cools to 64° C in 5 minutes and
to 52° C in 10 minutes. The temperature of the body after
15 minutes will be
(a) 42.7° C (b) 35° C (c) 47° (d) 40° C
Q.8 A 5 cm thick ice block is there on the surface of water in a
lake. The temperature of air is – 10° C; how much time it
will take to double the thickness of the block
(L = 80 cal/g, K
ice
 = 0.004 erg/s-k, d
ice
 = 0.92 g cm
–3
)
(a) 1 hour (b) 191 hours
. (c) 19.1 hours (d) 1.91 hours
Q.9 A cylindrical rod with one end in a steam chamber and the
other end in ice results in melting of 0.1 gm of ice per
second. If the rod is replaced by another with half the length
and double the radius of the first and if the thermal
conductivity of material of second rod is 
1
4
 that of first,
the rate at which ice melts in gm/sec will be
(a) 3.2 (b) 1.6 (c) 0.2 (d) 0.1
Q.10 An ice box used for keeping eatable cold has a total wall
area of 1 metre
2
 and a wall thickness of 5.0 cm. The thermal
conductivity of the ice box is K = 0.01 joule/metre °C. It
is filled with ice at 0° C along with eatables on a day when
the temperature is 30°C. The latent heat of fusion of ice is
334 × 10
3
 joules/kg. The amount of ice melted in one day
is  (1 day =  86,400 seconds)
(a) 776 gm (b) 7760 gm
(c) 11520 gm (d) 1552 gm
Q.11 A solid copper sphere (density r and specific heat capacity
c) of radius r at an initial temperature 200 K is suspended
inside a chamber whose walls are at almost 0 K. The time
required (in µ s) for the temperature of the sphere to drop
to 100 K is
(a)
72
7
rc r
s
(b)
7
72
rc r
s
(c)
27
7
rc r
s
(d)
7
27
rc r
s
Q.12 Four rods of identical cross-sectional area and made from
the same metal form the sides of square. The temperature
of two diagonally opposite points  are T and 2T
respectively in the steady state. Assuming that only heat
conduction takes place, what will be the temperature
difference between other two points
(a)
21
2
T
+
(b)
2
21
T
+
(c)0 (d) None of these
Q.13 Consider two hot bodies B
1
 and B
2 
which have temperature
100° C  and 80° C respectively at t = 0. The temperature
of surroundings is 40° C. The ratio of the respective rates
of cooling R
1
 and R
2
 of these two bodies at t = 0 will be
(a) R
1
 : R
2
 = 3 : 2 (b) R
1
 : R
2
 = 5 : 4
(c) R
1
 : R
2
 = 2 : 3 (d) R
1
 : R
2
 = 4 : 5
DPP/ P 23
3
Q.14A body cools from 60° C to 50° C in 10 minutes. If the
room temperature is 25° C and assuming Newton's law of
cooling to hold good, the temperature of the body at the
end of the next 10 minutes will be
(a) 38.5° C (b) 40° C (c) 42.85° C (d) 45° C
Q.15The rates of cooling of two different liquids put in exactly
similar calorimeters and kept in identical surroundings are the
same if
(a) The masses of the liquids are equal
(b) Equal masses of the liquids at the same temperature
are taken
(c) Different volumes of the liquids at the same
temperature are taken
(d) Equal volumes of the liquids at the same temperature
are taken
Q.16For cooking the food, which of the following type of
utensil is most suitable
(a) High specific heat and low conductivity
(b) High specific heat and high conductivity
(c) Low specific heat and low conductivity
(d) Low specific heat and high conductivity
Q.17 Two rods A and B are of equal lengths. Their ends are kept
between the same temperature and their area of cross-
sections are A
1
 and A
2
 and thermal conductivities K
1
 and
K
2
. The rate of heat transmission in the two rods will be
equal, if
(a)
1 2 21
K A KA = (b)
1 1 22
K A KA =
(c)
12
KK = (d)
22
1 1 22
K A KA =
Q.18 While measuring the thermal conductivity of a liquid, we
keep the upper part hot and lower part cool, so that
(a) Convection may be stopped
(b) Radiation may be stopped
(c) Heat conduction is easier downwards
(d) It is easier and more convenient to do so
Q.19When fluids are heated from the bottom, convection
currents are produced because
(a) Molecular motion of fluid becomes aligned
(b) Molecular collisions take place within the fluid
(c) Heated fluid becomes more dense than the cold fluid
above it
(d) Heated fluid becomes less dense than the cold fluid
above it
Q.20 If between wavelength l and l + dl, e
l
 and a
l
 be the
emissive and absorptive powers of a body and E
l
 be the
emissive power of a perfectly black body, then according
to Kirchoff’s law, which is true
(a) e aE
l ll
== (b)eEa
lll
=
(c) e aE
l ll
= (d) e aE
l ll
 = constant
Q.21 Two thermometers A and B are exposed in sunlight. The
bulb of A is painted black, But that of B is not painted. The
correct statement regarding this case is
(a) Temperature of A will rise faster than B but the final
temperature will be the  same in both
(b) Both A and B show equal rise in beginning
(c) Temperature of A will remain more than B
(d) Temperature of B will rise faster
DIRECTIONS (Q.22-Q.24) : In the following questions, more
than one of the answers  given are correct. Select the correct
answers and mark it according to the following codes:
Codes :
(a) 1, 2 and 3 are correct (b) 1 and 2 are correct
(c) 2 and 4 are correct (d) 1 and 3 are correct
Q.22 Two bodies A and B have thermal emissivities of 0.01 and
0.81 respectively . The outer surface areas of the two bodies
are the same. The two bodies emit total radiant power at
the  same rate. The wavelength 
B
? corresponding to
maximum spectral radiancy in the radiation from B is
shifted from the wavelength corresponding to maximum
spectral radiancy in the radiation from A, by 1.00 mm. If
the temperature of A is 5802 K
(1) The temperature of B is 1934 K
(2) l
B
 = 1.5 mm
(3) The temperature of B is 11604 K
(4) The temperature of B is 2901 K
Q.23A cane is taken out from a refrigerator at 0°C. The
atmospheric temperature is 25°C. If t
1
 is the time taken to
heat from 0°C to 5°C and t
2
 is the time taken from 10°C
to    15°C, then the wrong statements are
(1) t
1
 > t
2
(2) t
1
 = t
2
(3) There is no relation (4) t
1
 < t
2
Page 4


DIRECTIONS (Q.1-Q.21) : There are 21 multiple choice
questions. Each question has 4 choices (a), (b), (c) and (d), out
of which ONLY ONE choice is correct.
Q.1 Two rods (one semi-circular and other straight) of same
material and of same cross-sectional area are joined as
shown in the figure. The points A and B are maintained at
different temperature. The ratio of the heat transferred
through a cross-section of a semi-circular rod to the heat
transferred through a cross section of the straight rod in a
given time is
(a) 2 : p
(b) 1 : 2
A B
Straight rod
S
emi
 circular ro
d
(c) p : 2
(d) 3 : 2
Q.2 A wall is made up of two layers A and B. The thickness of
the two layers is the same, but materials are different. The
thermal conductivity of A is double than that of B. In thermal
equilibrium the temperature difference between the two
ends is 36°C. Then the difference of temperature at the
two surfaces of A will be
(a) 6°C (b) 12°C (c) 18°C (d) 24°C
Q.3 A room is maintained at 20°C by a heater of resistance 20
ohm connected to 200 volt mains. The temperature is
uniform through out the room and heat is transmitted
through a glass window of area 1m
2
 and thickness 0.2 cm.
What will be the temperature outside? Given that thermal
conductivity K for glass is 0.2 cal/m/°C/sec and J = 4.2 J/
cal
(a) 15.24°C (b) 15.00°C
(c) 24.15°C (d) None of these
2
DPP/ P 23
Q.4 A composite metal bar of uniform section is made up of
length 25 cm of copper, 10 cm of nickel and 15 cm of
aluminium. Each part being in perfect thermal contact with
the adjoining part. The copper end of the composite rod is
maintained at 100°C and the aluminium end at 0°C. The
whole rod is covered with belt so that there is no heat loss
occurs at the sides. If K
Cu
 =  2K
Al
 and K
Al
 = 3K
Ni
, then
what will be the temperatures of Cu – Ni and Ni – Al
junctions respectively
Cu Ni Al
100° C 0° C
(a) 23.33°C and 78.8°C (b) 83.33°C and 20°C
(c) 50°C a nd 30°C (d) 30°C a nd 50°C
Q.5 Three rods of the same dimension have thermal
conductivities 3K, 2K and K. They are arranged as shown
in fig. with their ends at 100°C, 50°C and 20°C. The
temperature of their junction is
(a) 60°C
(b) 70°C
(c) 50°C
100°C
50°C
20°C
K
2K
3K
(d) 35°C
Q.6 A black body is at a temperature of 2880 K. The energy of
radiation emitted by this object with wavelength between
499 nm and 500 nm is U
1
, between 999 nm and 1000 nm
is U
2
 and between 1499 nm and 1500 nm is U
3
. The W ein's
constant b = 2.88 × 10
6
 nm K. Then
(a) U
1 
= 0 (b) U
3 
= 0 (c) U
1 
> U
2
(d) U
2 
> U
1
Q.7 A body initially at 80° C cools to 64° C in 5 minutes and
to 52° C in 10 minutes. The temperature of the body after
15 minutes will be
(a) 42.7° C (b) 35° C (c) 47° (d) 40° C
Q.8 A 5 cm thick ice block is there on the surface of water in a
lake. The temperature of air is – 10° C; how much time it
will take to double the thickness of the block
(L = 80 cal/g, K
ice
 = 0.004 erg/s-k, d
ice
 = 0.92 g cm
–3
)
(a) 1 hour (b) 191 hours
. (c) 19.1 hours (d) 1.91 hours
Q.9 A cylindrical rod with one end in a steam chamber and the
other end in ice results in melting of 0.1 gm of ice per
second. If the rod is replaced by another with half the length
and double the radius of the first and if the thermal
conductivity of material of second rod is 
1
4
 that of first,
the rate at which ice melts in gm/sec will be
(a) 3.2 (b) 1.6 (c) 0.2 (d) 0.1
Q.10 An ice box used for keeping eatable cold has a total wall
area of 1 metre
2
 and a wall thickness of 5.0 cm. The thermal
conductivity of the ice box is K = 0.01 joule/metre °C. It
is filled with ice at 0° C along with eatables on a day when
the temperature is 30°C. The latent heat of fusion of ice is
334 × 10
3
 joules/kg. The amount of ice melted in one day
is  (1 day =  86,400 seconds)
(a) 776 gm (b) 7760 gm
(c) 11520 gm (d) 1552 gm
Q.11 A solid copper sphere (density r and specific heat capacity
c) of radius r at an initial temperature 200 K is suspended
inside a chamber whose walls are at almost 0 K. The time
required (in µ s) for the temperature of the sphere to drop
to 100 K is
(a)
72
7
rc r
s
(b)
7
72
rc r
s
(c)
27
7
rc r
s
(d)
7
27
rc r
s
Q.12 Four rods of identical cross-sectional area and made from
the same metal form the sides of square. The temperature
of two diagonally opposite points  are T and 2T
respectively in the steady state. Assuming that only heat
conduction takes place, what will be the temperature
difference between other two points
(a)
21
2
T
+
(b)
2
21
T
+
(c)0 (d) None of these
Q.13 Consider two hot bodies B
1
 and B
2 
which have temperature
100° C  and 80° C respectively at t = 0. The temperature
of surroundings is 40° C. The ratio of the respective rates
of cooling R
1
 and R
2
 of these two bodies at t = 0 will be
(a) R
1
 : R
2
 = 3 : 2 (b) R
1
 : R
2
 = 5 : 4
(c) R
1
 : R
2
 = 2 : 3 (d) R
1
 : R
2
 = 4 : 5
DPP/ P 23
3
Q.14A body cools from 60° C to 50° C in 10 minutes. If the
room temperature is 25° C and assuming Newton's law of
cooling to hold good, the temperature of the body at the
end of the next 10 minutes will be
(a) 38.5° C (b) 40° C (c) 42.85° C (d) 45° C
Q.15The rates of cooling of two different liquids put in exactly
similar calorimeters and kept in identical surroundings are the
same if
(a) The masses of the liquids are equal
(b) Equal masses of the liquids at the same temperature
are taken
(c) Different volumes of the liquids at the same
temperature are taken
(d) Equal volumes of the liquids at the same temperature
are taken
Q.16For cooking the food, which of the following type of
utensil is most suitable
(a) High specific heat and low conductivity
(b) High specific heat and high conductivity
(c) Low specific heat and low conductivity
(d) Low specific heat and high conductivity
Q.17 Two rods A and B are of equal lengths. Their ends are kept
between the same temperature and their area of cross-
sections are A
1
 and A
2
 and thermal conductivities K
1
 and
K
2
. The rate of heat transmission in the two rods will be
equal, if
(a)
1 2 21
K A KA = (b)
1 1 22
K A KA =
(c)
12
KK = (d)
22
1 1 22
K A KA =
Q.18 While measuring the thermal conductivity of a liquid, we
keep the upper part hot and lower part cool, so that
(a) Convection may be stopped
(b) Radiation may be stopped
(c) Heat conduction is easier downwards
(d) It is easier and more convenient to do so
Q.19When fluids are heated from the bottom, convection
currents are produced because
(a) Molecular motion of fluid becomes aligned
(b) Molecular collisions take place within the fluid
(c) Heated fluid becomes more dense than the cold fluid
above it
(d) Heated fluid becomes less dense than the cold fluid
above it
Q.20 If between wavelength l and l + dl, e
l
 and a
l
 be the
emissive and absorptive powers of a body and E
l
 be the
emissive power of a perfectly black body, then according
to Kirchoff’s law, which is true
(a) e aE
l ll
== (b)eEa
lll
=
(c) e aE
l ll
= (d) e aE
l ll
 = constant
Q.21 Two thermometers A and B are exposed in sunlight. The
bulb of A is painted black, But that of B is not painted. The
correct statement regarding this case is
(a) Temperature of A will rise faster than B but the final
temperature will be the  same in both
(b) Both A and B show equal rise in beginning
(c) Temperature of A will remain more than B
(d) Temperature of B will rise faster
DIRECTIONS (Q.22-Q.24) : In the following questions, more
than one of the answers  given are correct. Select the correct
answers and mark it according to the following codes:
Codes :
(a) 1, 2 and 3 are correct (b) 1 and 2 are correct
(c) 2 and 4 are correct (d) 1 and 3 are correct
Q.22 Two bodies A and B have thermal emissivities of 0.01 and
0.81 respectively . The outer surface areas of the two bodies
are the same. The two bodies emit total radiant power at
the  same rate. The wavelength 
B
? corresponding to
maximum spectral radiancy in the radiation from B is
shifted from the wavelength corresponding to maximum
spectral radiancy in the radiation from A, by 1.00 mm. If
the temperature of A is 5802 K
(1) The temperature of B is 1934 K
(2) l
B
 = 1.5 mm
(3) The temperature of B is 11604 K
(4) The temperature of B is 2901 K
Q.23A cane is taken out from a refrigerator at 0°C. The
atmospheric temperature is 25°C. If t
1
 is the time taken to
heat from 0°C to 5°C and t
2
 is the time taken from 10°C
to    15°C, then the wrong statements are
(1) t
1
 > t
2
(2) t
1
 = t
2
(3) There is no relation (4) t
1
 < t
2
4
DPP/ P 23
Q.24 The rate of loss of heat from a body cooling under conditions
of forced convection is proportional to its
(1) surface area
(2) excess of temperature over that of surrounding
(3) heat capacity
(4) absolute temperature
DIRECTIONS (Q.25-Q.27) : Read the passage given below
and answer the questions that follows :
A brass ball of mass 100g is heated to 100°C and then dropped
into 200g of turpentine in a calorimeter at 15°C. The final
temperature is found to be 23°C. Take specific heat of brass as
0.092 cal/g°C and water equivalent of calorimeter as 4g.
Q.25 The specific heat of turpentine is
(a) 0.42 cal/g°c (b) 0.96 cal/g°c
(c) 0.72 cal/g°c (d) 0.12 cal/g°c
Q.26 Heat lost by the ball is approximately
(a) 810 cal (b) 610 cal
(c) 710 cal (d) 510 cal
Q.27 Heat gained by turpentine and calorimeter is approximately
(a) 810 cal (b) 610 cal
(c) 710 cal (d) 510 cal
DIRECTIONS (Q.28-Q.30) : Each of these questions contains two
sta tements: S tatem ent-1 (Ass ertio n) an d S tatement-2 (Reaso n). E ach
of these questions has four alternative choices, only one of which is
the correct answer . Y ou have to select the correct choice.
(a) Statement-1 is True, Statement-2 is True; Statement-2 is a
correct explanation for  Statement-1.
(b) Statement-1 is True, Statement-2 is True; Statement-2 is
NOT a correct explanation for Statement-1.
(c) Statement -1 is False, Statement-2 is True.
(d) Statement -1 is True, Statement-2 is False.
Q.28 Statement-1 : The equivalent thermal conductivity of two
plates of same thickness in contact (series) is less than
the smaller value of thermal conductivity.
Statement-2 : For two plates of equal thickness in contact
(series) the equivalent thermal conductivity is given by
12
2 11
=+
K KK
Q.29 Statement-1 : The absorbance of a perfect black body is unity .
Statement-2 : A perfect black body when heated emits
radiations of all possible wavelengths at that temperature.
Q.30Statement-1 : As temperature of a black body is raised,
wavelength corresponding to maximum energy reduces.
Statement-2 : Higher temperature would mean higher
energy and hence higher wavelength.