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Did you ever think about why a metal spoon is colder than a wooden spoon even at the same temperature? Or why blacksmiths heat iron rings before placing them on wooden wheels? Thermal Properties of Matter Class 11 NCERT Solutions will provide you with answers to these questions. In this chapter, we learn about how heat moves, why the temperature sometimes does not change despite the addition of heat, and the physics involved in everyday processes such as sea breezes and boiling water. With step-by-step solutions, learning is a breeze and successful.
The NCERT solution for class 11 physics thermal properties of matter is created by experienced faculty to give precise and detailed solutions to each and every NCERT exercise problem. Students can practice important questions and learn the key concepts with the help of these thermal properties of matter NCERT solutions for class 11 prior to exams. These step-by-step solutions simplify the learning process and are free to access below.
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Answer:
The relation between Kelvin and Celcius scale is T K = T C + 273.15
Triple Point of Neon in Kelvin T K = 24.57 K
Triple Point of Neon in Celcius T C = T K -273.15 = 24.57 -273.15 =-248.58 o C
Triple Point of carbon dioxide in Kelvin T K = 216.55 K
Triple Point of carbon dioxide in Celcius T C = T K -273.15 = 216.55 - 273.15 = -56.60 o C
The relation between Celcius and Fahrenheit scale is
Triple Point of Neon in Fahrenheit is
T F = -415.44 o C
Triple Point of carbon dioxide in Fahrenheit is
T F = -69.88 o C
Answer:
200 A = 273 K
350 B = 273 K
Equating T K From the above two equations we have
The resistance is
Answer:
R 0 =
R =
Putting the above values in the given equation we have
For R =
Q. 10.4 (a) Answer the following:
(a) The triple-point of water is a standard fixed point in modern thermometry. Why ? What is wrong in taking the melting point of ice and the boiling point of water as standard fixed points (as was originally done in the Celsius scale)?
Answer:
Unlike the melting point of ice and boiling point of water, the triple point of water has a fixed value of 273.16 K. The melting point of ice and boiling point of water vary with pressure.
Q. 10.4 (b) Answer the following :
Answer:
The other fixed point on the Kelvin scale is 0 K. 0K is the absolute zero
Q. 10.4 (c) Answer the following :
(c) The absolute temperature (Kelvin scale)
Why do we have
Answer:
This is because 0 o C on the Celcius scale corresponding to the melting point at standard pressure is equal to 273.15 K whereas 273.16 K is the triple point of water. The triple point of water is 0.01 0 C , not 0 0 C
Q. 10.4 (d) Answer the following :
Answer:
Let at a certain temperature the reading on Fahrenheit and Kelvin Scale be T F and T K respectively
Let at another temperature the reading on Fahrenheit and Kelvin Scale be T' F and T' K respectively
Subtracting equation (ii) from (i)
For T K - T' K = 1 K, T F - T' F = 9/5
Therefore corresponding to 273.16 K the absolute scale whose unit interval size is equal to that of the Fahrenheit scale
Temperature
|
Pressure
Thermometer A
|
Pressure
Thermometer B
|
Triple-point of water
| ||
Normal melting point of sulphur
|
(a) What is the absolute temperature of normal melting point of sulphur as read by thermometers A and B?
Answer:
As the moles of oxygen and hydrogen inside the thermometers and the volume occupied by the gases remain constant P/T would remain constant.
The triple point of water(T 1 ) = 273.16 K
Pressure in thermometer A at a temperature equal to the triple point of water (P 1 ) =
Pressure in thermometer A at a temperature equal to Normal melting point of sulphur (P 2 ) =
The normal melting point of sulphur as read by thermometer A T 2 would be given as
Pressure in thermometer B at a temperature equal to the triple point of water (P1' ) =
Pressure in thermometer B at a temperature equal to Normal melting point of sulphur (P2' ) =
The normal melting point of sulphur as read by thermometer B T2' would be given as
Temperature
|
Pressure
Thermometer A
|
Pressure
Thermometer B
|
Triple-point of water
| ||
Normal melting point of sulphur
|
(b) What do you think is the reason behind the slight difference in answers of thermometers A and B? (The thermometers are not faulty). What further procedure is needed in the experiment to reduce the discrepancy between the two readings?
Answer:
The slight difference in answers of thermometers A and B occur because the gases used in the thermometers are not ideal gases. To reduce this discrepancy the experiments should be carried out at low pressures where the behaviour of real gases tend close to that of ideal gases.
Answer:
At 27 o C the 63 cm (l 1 ) mark on the steel tape would be measuring exactly 63 cm as the tape is calibrated at 27 o C
Coefficient of linear expansion of steel
Actual length when the scale is giving a reading of 63 cm on at 45 o C is l 2
The actual length of the steel rod on a day when the temperature is 45 o C is 63.013608 cm.
Length of the same steel rod on a day when the temperature is 63 cm.
Answer:
Diameter of the steel shaft at 27 o C (T 1 ) d 1 = 8.70 cm
The diameter of the central hole in the wheel d 2 = 8.69 cm
Coefficient of linear expansion of the steel
The wheel will slip on the shaft when the diameter of the steel shaft becomes equal to the diameter of the central hole in the wheel.
Let this happen at temperature T
Answer:
Coefficient of linear expansion of copper
Coefficient of superficial expansion of copper is
Diameter of the hole at 27 o C (d 1 ) = 4.24 cm
Area of the hole at 227 o C is
Let the diameter at 227 o C be d 2
Change in diameter is d 2 -d 1 = 4.24 -4.254 = 0.014 cm.
Answer:
Youngs Modulus of Brass,
Co-efficient of linear expansion of Brass,
The diameter of the given brass wire, d = 2.0 mm
Length of the given brass wire, l = 1.8 m
Initial Temperature T 1 = 27 o C
Final Temperature T 2 = -39 o C
The tension developed in the wire is 378 N. The negative sign signifies this tension is inward.
Answer:
Length of the rods l = 50 cm
Co-efficient of linear expansion of brass,
Co-efficient of linear expansion of steel,
Initial Temperature T 1 = 40.0 o C
Final Temperature T 2 = 250 o C
Change in length of brass rod is
Change in length of the steel rod is
Change in length of the combined rod is
Answer:
Coefficient of volume expansion of glycerine is
Let initial volume and mass of a certain amount of glycerine be V and m respectively.
Initial density is
Change in volume for a 30 o C rise in temperature will be
Final Density is
Fractional Change in density is
The negative sign signifies with an increase in temperature density will decrease.
Answer:
Power of the drilling machine, P = 10 kW
Time. t = 2.5 min
Total energy dissipated E is
Thermal energy absorbed by aluminium block is
Mass of the aluminium block, m = 8.0 kg
Specific heat of aluminium, c = 0.91 J g -1 K -1
Let rise in temperature be
Answer:
Mass of copper block m = 2.5 kg
Initial Temperature of the copper block, T 1 = 500 o C
Final Temperature of Copper block, T 2 = 0 o C
Specific heat of copper, c = 0.39 J g -1 K -1
Thermal Energy released by the copper block is
Latent heat of fusion of water, L = 335 j g -1
Amount of ice that can melt is
1.455 kg of ice can melt using the heat released by the copper block.
Answer:
Let the specific heat of the metal be C.
Mass of metal block m = 200 g
Initial Temperature of metal block = 150 o C
Final Temperature of metal block = 40 o C
The heat released by the block is
Initial Temperature of the calorimeter and water = 27 o C
Final Temperature of the calorimeter and water = 40 o C
Amount of water = 150 cm
Mass of water = 150 g
Water equivalent of calorimeter = 25 g
Specific heat of water = 4.186 J g -1 K -1
Heat absorbed by the Calorimeter and water is
The heat absorbed by the Calorimeter and water is equal to the heat released by the block
The above value would be lesser than the actual value since some heat must have been lost to the surroundings as well which we haven't accounted for.
Q. 10.15 Given below are observations on molar specific heats at room temperature of some common gases.
Gas Molar specific heat (Cv )
Hydrogen 4.87
Nitrogen 4.97
Oxygen 5.02
Nitric oxide 4.99
Carbon monoxide 5.01
Chlorine 6.17
The measured molar specific heats of these gases are markedly different from those for monatomic gases. Typically, molar specific heat of a monatomic gas is
Answer:
Monoatomic gases have only translational degree of freedom but diatomic gases have rotational degrees of freedom as well. The temperature increases with increase in the spontaneity of motion in all degrees. Therefore, to increase the temperature of diatomic gases more energy is required than that required to increase the temperature of monoatomic gases by the same value owing to higher degrees of freedom in diatomic gases.
If we only consider rotational modes of freedom the molar specific heat of the diatomic gases would be given as
The number of degrees of freedom = 5 (3 translational and 2 rotational)
The values given in the table are more or less in accordance with the above calculated one. The larger deviation from the calculated value in the case of chlorine is because of the presence of vibrational motion as well.
Answer:
Initial Temperature of the boy = 101 o F
Final Temperature of the boy = 98 o F
Change in Temperature is
Mass of the child is m = 30 kg
Specific heat of human body = 1000 cal kg -1 o C -1
Heat released is
Latent heat of evaporation of water = 580 cal g -1
The amount of heat lost by the body of the boy has been absorbed by water.
Let the mass of water which has evaporated be m'
Time in which the water has evaporated, t = 20 min.
The rate of evaporation is m'/t
Answer:
Side of the box s = 30 cm
Area available for conduction A
A = 6s 2
A=6(30) 2
A=5400 cm 2 = 0.54 m 2
Temperature difference = 45 o C
Co-efficient of thermal conductivity of thermacole is k = 0.01 J s -1 m -1 K -1
Width of the box is d = 5 cm
Heat absorbed by the box in 6 hours is
The heat of fusion of water is
The amount of ice which has melted is m'
Amount of ice left after 6 hours = 4 - 0.313 = 3.687 kg
Answer:
The rate at which water boils, R = 6.0 kg min -1
The heat of vaporisation of water,
The rate at which heat enters the boiler
The base area of the boiler, A = 0.15 m 2
Thickness, l = 1.0 cm
Thermal conductivity of brass
The temperature inside the boiler = Boiling point of water = 100 o C
Let the temperature of the flame in contact with the boiler be T
The amount of heat flowing into the boiler is
The temperature of the flame in contact with the boiler is 237.98 o C
Q. 10.19 (a) Explain why :
(a) a body with large reflectivity is a poor emitter
Answer:
A body with a large reflectivity is a poor absorber. As we know a body which is a poor absorber will as well be a poor emitter. Therefore, a body with large reflectivity is a poor emitter.
Q .10.19 (b) Explain why :
(b) a brass tumbler feels much colder than a wooden tray on a chilly day
Answer:
Brass is a good conductor of heat. Therefore once someone touches brass heat from their body flows into it and it feels cold, in case of a wooden tray, no such conduction of heat from the body takes place as wood is a very poor conductor of heat.
Q. 10.19 (c) Explain why :
Answer:
An optical pyrometer relates the brightness of a glowing body with its temperature. In the open because of other sources of light the sensor in the optical pyrometer does not detect the true brightness of a red hot piece of iron and thus does not predict its temperature correctly whereas in the furnace the piece of iron is the only source of light and the sensor detects its brightness correctly thus giving the correct value of the temperature.
Q. 10.19 (d) Explain why :
(d) the earth without its atmosphere would be inhospitably cold
Answer:
The sun rays contain infrared radiations. These are reflected back by the lower part of the atmosphere after being reflected by the surface of the earth and are trapped inside the atmosphere thus maintaining the Earth's temperature at a hospitable level. Without these rays being trapped the temperature of the earth will go down severely and thus the Earth without its atmosphere would be inhospitably cold.
Q. 10.19 (e) Explain why :
Answer:
Heating systems based on the circulation of steam are more efficient in warming a building than those based on the circulation of hot water because the same amount of steam at 100 o C contains more energy available for heat dissipation than the same amount of water at 100 o C in the form of latent heat of vaporization.
Answer:
Let a body initially be at temperature T 1
Let its final Temperature be T 2
Let the surrounding temperature be T 0
Let the temperature change in time t.
According to Newton's Law of cooling
where K is a constant.
We have been given that the body cools from 80 o C to 50 o C in 5 minutes when the surrounding temperature is 20 o C.
T 2 = 50 o C
T 1 = 80 o C
T 0 = 20 o C
t = 5 min = 300 s.
For T 1 = 60 o C and T 2 = 30 o C we have
The body will take 10 minutes to cool from 60 o C to 30 o C at the surrounding temperature of 20 o C.
Q1:
When 100 g of liquid A at 100oC is added to 50 g of liquid B at a temperature of 75oC, the temperature of the mixture becomes 90oC. The temperature of the mixture (in oC), if 100 g of liquid A at 100oC is added to 50 g of liquid B at 50oC, will be :
Answer:
Specific Heat -
From (1) & (2)
Q2:
If the length of cylinder on heating increases by 2% then the area of base of cylinder will increase by
Answer: Assuming the initial length of the cylinder is
Q3: A cylindrical metal rod of length L0 is shaped into a ring with a small gap as shown in Figure. On heating the system,
A. x will decrease, R will increase
B. Both x and R will decrease
C. Both x and R will increase
D. R will increase, x will remain same
Answer:
Linear Expansion - When a solid is heated and its length increases, then the Expansion is called linear Expansion.
On the heating, the system x and R both will increase since the expansion of isotropic solids is similar to true photographic enlargement.
Q4:
The coefficient of thermal expansion of a rod varies with temperature as
Answer:
We know coefficient of thermal expansion is given as
Q5:
A red hot iron (mass 25 g) has a temperature of 100ºC. It is immersed in a mixture of ice and water at thermal equilibrium. The volume of the mixture is found to be reduced by
Given specific gravity of ice = 0.92, specific gravity of water at
Answer:
As the ice melts its density changes which causes change in volume. Let m g of ice melt.
Power radiated by a body depends on its temperature
Be consistent with units:- Temperature in Kelvin, mass in kg, heat in Joules
Practice diagrams & graphs:-
Cooling curves, temperature vs time, phase change graphs
Visuals serve to address theory and concept-type questions
One question can be expected for NEET exam from the chapter Thermal Properties of Matter. Students can practice more questions from previous year NEET papers.
One question may be asked from Class 11 Physics chapter 10 Thermal Properties of Matter for JEE Main exam. This is one important chapter for KVPY and NSEP exms. Students can get more problems on the chapter from the NCERT Exemplar.
Topics covered in NCERT book Class 11 chapter Thermal Properties of Matter are-
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