NCERT Solutions

10.1 The triple points of neon and carbon dioxide are 24.57 K and 216.55 K respectively. Express these temperatures on the Celsius and Fahrenheit scales.

10.1 The triple points of neon and carbon dioxide are 24.57 K and 216.55 K respectively. Express these temperatures on the Celsius and Fahrenheit scales.

10.2 Two absolute scales A and B have triple points of water defined to be 200 A and 350 B. What is the relation between $T_A$ and $T_B$?

10.2 Two absolute scales A and B have triple points of water defined to be 200 A and 350 B. What is the relation between $T_A$ and $T_B$?

10.3 The electrical resistance in ohms of a certain thermometer varies with temperature according to the approximate law : $R = R_o[1 + \alpha(T - T_o)]$

The resistance is $101.6 \Omega$ at the triple-point of water 273.16 K, and $165.5 \Omega$ at the normal melting point of lead (600.5 K). What is the temperature when the resistance is $123.4 \Omega$?

10.3 The electrical resistance in ohms of a certain thermometer varies with temperature according to the approximate law : $R = R_o[1 + \alpha(T - T_o)]$

The resistance is $101.6 \Omega$ at the triple-point of water 273.16 K, and $165.5 \Omega$ at the normal melting point of lead (600.5 K). What is the temperature when the resistance is $123.4 \Omega$?

10.6 A steel tape 1 m long is correctly calibrated for a temperature of $27.0^{\circ}$C. The length of a steel rod measured by this tape is found to be 63.0 cm on a hot day when the temperature is $45.0^{\circ}$C. What is the actual length of the steel rod on that day ? What is the length of the same steel rod on a day when the temperature is $27.0^{\circ}$C ? Coefficient of linear expansion of steel $= 1.20 \times 10^{-5} \text{ K}^{-1}$.

10.6 A steel tape 1 m long is correctly calibrated for a temperature of $27.0^\circ\text{C}$. The length of a steel rod measured by this tape is found to be 63.0 cm on a hot day when the temperature is $45.0^\circ\text{C}$. What is the actual length of the steel rod on that day? What is the length of the same steel rod on a day when the temperature is $27.0^\circ\text{C}$? Coefficient of linear expansion of steel = $1.20 \times 10^{-5} \text{ K}^{-1}$.

10.7 A large steel wheel is to be fitted on to a shaft of the same material. At $27^{\circ}$C, the outer diameter of the shaft is 8.70 cm and the diameter of the central hole in the wheel is 8.69 cm. The shaft is cooled using 'dry ice'. At what temperature of the shaft does the wheel slip on the shaft? Assume coefficient of linear expansion of the steel to be constant over the required temperature range : $\alpha_{steel} = 1.20 \times 10^{-5} \text{ K}^{-1}$.

10.7 A large steel wheel is to be fitted on to a shaft of the same material. At $27^\circ\text{C}$, the outer diameter of the shaft is 8.70 cm and the diameter of the central hole in the wheel is 8.69 cm. The shaft is cooled using 'dry ice'. At what temperature of the shaft does the wheel slip on the shaft? Assume coefficient of linear expansion of the steel to be constant over the required temperature range : $\alpha_{steel} = 1.20 \times 10^{-5} \text{ K}^{-1}$.

10.8 A hole is drilled in a copper sheet. The diameter of the hole is 4.24 cm at $27.0^\circ\text{C}$. What is the change in the diameter of the hole when the sheet is heated to $227^\circ\text{C}$? Coefficient of linear expansion of copper = $1.70 \times 10^{-5} \text{ K}^{-1}$.

10.8 A hole is drilled in a copper sheet. The diameter of the hole is 4.24 cm at $27.0^{\circ}$C. What is the change in the diameter of the hole when the sheet is heated to $227^{\circ}$C ? Coefficient of linear expansion of copper $= 1.70 \times 10^{-5} \text{ K}^{-1}$.

10.9 A brass wire 1.8 m long at $27^\circ\text{C}$ is held taut with little tension between two rigid supports. If the wire is cooled to a temperature of $-39^\circ\text{C}$, what is the tension developed in the wire, if its diameter is 2.0 mm? Co-efficient of linear expansion of brass = $2.0 \times 10^{-5} \text{ K}^{-1}$; Young's modulus of brass = $0.91 \times 10^{11} \text{ Pa}$.

10.9 A brass wire 1.8 m long at $27^{\circ}$C is held taut with little tension between two rigid supports. If the wire is cooled to a temperature of $-39^{\circ}$C, what is the tension developed in the wire, if its diameter is 2.0 mm ? Co-efficient of linear expansion of brass $= 2.0 \times 10^{-5} \text{ K}^{-1}$; Young's modulus of brass $= 0.91 \times 10^{11} \text{ Pa}$.

10.10 A brass rod of length 50 cm and diameter 3.0 mm is joined to a steel rod of the same length and diameter. What is the change in length of the combined rod at $250^{\circ}$C, if the original lengths are at $40.0^{\circ}$C ? Is there a 'thermal stress' developed at the junction? The ends of the rod are free to expand (Co-efficient of linear expansion of brass $= 2.0 \times 10^{-5} \text{ K}^{-1}$, steel $= 1.2 \times 10^{-5} \text{ K}^{-1}$).

10.10 A brass rod of length 50 cm and diameter 3.0 mm is joined to a steel rod of the same length and diameter. What is the change in length of the combined rod at $250^\circ\text{C}$, if the original lengths are at $40.0^\circ\text{C}$? Is there a 'thermal stress' developed at the junction? The ends of the rod are free to expand (Co-efficient of linear expansion of brass = $2.0 \times 10^{-5} \text{ K}^{-1}$, steel = $1.2 \times 10^{-5} \text{ K}^{-1}$).

10.11 The coefficient of volume expansion of glycerine is $49 \times 10^{-5} \text{ K}^{-1}$. What is the fractional change in its density for a $30^{\circ}$C rise in temperature ?

10.11 The coefficient of volume expansion of glycerine is $49 \times 10^{-5} \text{ K}^{-1}$. What is the fractional change in its density for a $30^\circ\text{C}$ rise in temperature?

10.12 A 10 kW drilling machine is used to drill a bore in a small aluminium block of mass 8.0 kg. How much is the rise in temperature of the block in 2.5 minutes, assuming 50% of power is used up in heating the machine itself or lost to the surroundings. Specific heat of aluminium = $0.91 \text{ J g}^{-1} \text{ K}^{-1}$.

10.12 A 10 kW drilling machine is used to drill a bore in a small aluminium block of mass 8.0 kg. How much is the rise in temperature of the block in 2.5 minutes, assuming 50% of power is used up in heating the machine itself or lost to the surroundings. Specific heat of aluminium $= 0.91 \text{ J g}^{-1} \text{ K}^{-1}$.

10.13 A copper block of mass 2.5 kg is heated in a furnace to a temperature of $500^{\circ}$C and then placed on a large ice block. What is the maximum amount of ice that can melt? (Specific heat of copper $= 0.39 \text{ J g}^{-1} \text{ K}^{-1}$; heat of fusion of water $= 335 \text{ J g}^{-1}$).

10.13 A copper block of mass 2.5 kg is heated in a furnace to a temperature of $500^\circ\text{C}$ and then placed on a large ice block. What is the maximum amount of ice that can melt? (Specific heat of copper = $0.39 \text{ J g}^{-1} \text{ K}^{-1}$; heat of fusion of water = $335 \text{ J g}^{-1}$).

10.14 In an experiment on the specific heat of a metal, a 0.20 kg block of the metal at $150^\circ\text{C}$ is dropped in a copper calorimeter (of water equivalent 0.025 kg) containing $150 \text{ cm}^3$ of water at $27^\circ\text{C}$. The final temperature is $40^\circ\text{C}$. Compute the specific heat of the metal. If heat losses to the surroundings are not negligible, is your answer greater or smaller than the actual value for specific heat of the metal?

10.14 In an experiment on the specific heat of a metal, a 0.20 kg block of the metal at $150^{\circ}$C is dropped in a copper calorimeter (of water equivalent 0.025 kg) containing $150 \text{ cm}^3$ of water at $27^{\circ}$C. The final temperature is $40^{\circ}$C. Compute the specific heat of the metal. If heat losses to the surroundings are not negligible, is your answer greater or smaller than the actual value for specific heat of the metal ?

10.15 Given below are observations on molar specific heats at room temperature of some common gases.

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 $2.92 \text{ cal/mol K}$. Explain this difference. What can you infer from the somewhat larger (than the rest) value for chlorine?

10.15 Given below are observations on molar specific heats at room temperature of some common gases.

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 $2.92 \text{ cal/mol K}$. Explain this difference. What can you infer from the somewhat larger (than the rest) value for chlorine ?

10.16 A child running a temperature of $101^\circ\text{F}$ is given an antipyrin (i.e. a medicine that lowers fever) which causes an increase in the rate of evaporation of sweat from his body. If the fever is brought down to $98^\circ\text{F}$ in 20 minutes, what is the average rate of extra evaporation caused, by the drug. Assume the evaporation mechanism to be the only way by which heat is lost. The mass of the child is 30 kg. The specific heat of human body is approximately the same as that of water, and latent heat of evaporation of water at that temperature is about $580 \text{ cal g}^{-1}$.

10.16 A child running a temperature of $101^{\circ}$F is given an antipyrin (i.e. a medicine that lowers fever) which causes an increase in the rate of evaporation of sweat from his body. If the fever is brought down to $98^{\circ}$F in 20 minutes, what is the average rate of extra evaporation caused, by the drug. Assume the evaporation mechanism to be the only way by which heat is lost. The mass of the child is 30 kg. The specific heat of human body is approximately the same as that of water, and latent heat of evaporation of water at that temperature is about $580 \text{ cal g}^{-1}$.

10.17 A 'thermacole' icebox is a cheap and an efficient method for storing small quantities of cooked food in summer in particular. A cubical icebox of side 30 cm has a thickness of 5.0 cm. If 4.0 kg of ice is put in the box, estimate the amount of ice remaining after 6 h. The outside temperature is $45^\circ\text{C}$, and co-efficient of thermal conductivity of thermacole is $0.01 \text{ J s}^{-1} \text{ m}^{-1} \text{ K}^{-1}$. [Heat of fusion of water = $335 \times 10^3 \text{ J kg}^{-1}$]

10.17 A 'thermacole' icebox is a cheap and an efficient method for storing small quantities of cooked food in summer in particular. A cubical icebox of side 30 cm has a thickness of 5.0 cm. If 4.0 kg of ice is put in the box, estimate the amount of ice remaining after 6 h. The outside temperature is $45^{\circ}$C, and co-efficient of thermal conductivity of thermacole is $0.01 \text{ J s}^{-1} \text{m}^{-1} \text{K}^{-1}$. [Heat of fusion of water $= 335 \times 10^3 \text{ J kg}^{-1}$]

10.18 A brass boiler has a base area of $0.15 \text{ m}^2$ and thickness 1.0 cm. It boils water at the rate of $6.0 \text{ kg/min}$ when placed on a gas stove. Estimate the temperature of the part of the flame in contact with the boiler. Thermal conductivity of brass = $109 \text{ J s}^{-1} \text{ m}^{-1} \text{ K}^{-1}$; Heat of vaporisation of water = $2256 \times 10^3 \text{ J kg}^{-1}$.

10.18 A brass boiler has a base area of $0.15 \text{ m}^2$ and thickness 1.0 cm. It boils water at the rate of $6.0 \text{ kg/min}$ when placed on a gas stove. Estimate the temperature of the part of the flame in contact with the boiler. Thermal conductivity of brass $= 109 \text{ J s}^{-1} \text{m}^{-1} \text{K}^{-1}$; Heat of vaporisation of water $= 2256 \times 10^3 \text{ J kg}^{-1}$.

10.20 A body cools from $80^\circ\text{C}$ to $50^\circ\text{C}$ in 5 minutes. Calculate the time it takes to cool from $60^\circ\text{C}$ to $30^\circ\text{C}$. The temperature of the surroundings is $20^\circ\text{C}$.

10.20 A body cools from $80^{\circ}$C to $50^{\circ}$C in 5 minutes. Calculate the time it takes to cool from $60^{\circ}$C to $30^{\circ}$C. The temperature of the surroundings is $20^{\circ}$C.