## A body cools from 80 °C to 50 °C in 5 minutes. Calculate the time it takes to cool from 60 °C to 30 °C. The temperature of the surroundings is 20 °C. | Learn NCERT solution | Education portal Class 11 Physics | Study online Unit-11 Thermal Properties of Matter

Q.22:- A body cools from 80 °C to 50 °C in 5 minutes. Calculate the time it takes to cool from 60 °C to 30 °C. The temperature of the surroundings…

## Explain why: (a) a body with large reflectivity is a poor emitter (b) a brass tumbler feels much colder than a wooden tray on a chilly day (c) an optical pyrometer (for measuring high temperatures) calibrated for an ideal black body radiation gives too low a value for the temperature of a red hot iron piece in the open, but gives a correct value for the temperature when the same piece is in the furnace (d) the earth without its atmosphere would be inhospitably cold (e) heating systems based on circulation of steam are more efficient in warming a building than those based on circulation of hot water | Learn NCERT solution | Education portal Class 11 Physics | Study online Unit-11 Thermal Properties of Matter

Q.21:-  Explain why: (a) a body with large reflectivity is a poor emitter (b) a brass tumbler feels much colder than a wooden tray on a chilly day (c) an optical…

## A brass boiler has a base area of 0.15 m2 and thickness 1.0 cm. It boils water at the rate of 6.0 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 J s –1 m–1 K–1; Heat of vaporisation of water = 2256 × 103 J kg–1. | Learn NCERT solution | Education portal Class 11 Physics | Study online Unit-11 Thermal Properties of Matter

Q.20:- A brass boiler has a base area of 0.15 m2 and thickness 1.0 cm. It boils water at the rate of 6.0 kg/min when placed on a gas stove. Estimate…

## A ‘thermacole’ icebox is a cheap and 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 °C, and co-efficient of thermal conductivity of thermacole is 0.01 J s–1 m–1 K–1. | Learn NCERT solution | Education portal Class 11 Physics | Study online Unit-11 Thermal Properties of Matter

Q.19:- A ‘thermacole’ icebox is a cheap and efficient method for storing small quantities of cooked food in summer in particular. A cubical icebox of side 30 cm has a thickness…

## A child running a temperature of 101°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 °F in 20 min, 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 cal g–1. | Learn NCERT solution | Education portal Class 11 Physics | Study online Unit-11 Thermal Properties of Matter

Q.18:- A child running a temperature of 101°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…

## Answer the following questions based on the P–T phase diagram of CO2: (a) CO2 at 1 atm pressure and temperature – 60 °C is compressed isothermally. Does it go through a liquid phase? (b) What happens when CO2 at 4 atm pressure is cooled from room temperature at constant pressure? (c) Describe qualitatively the changes in a given mass of solid CO2 at 10 atm pressure and temperature –65 °C as it is heated up to room temperature at constant pressure. (d) CO2 is heated to a temperature 70° C and compressed isothermally. What changes in its properties do you expect to observe? | Learn NCERT solution | Education portal Class 11 Physics | Study online Unit-11 Thermal Properties of Matter

Q.17:- Answer the following questions based on the P–T phase diagram of CO2: (a) CO2 at 1 atm pressure and temperature – 60 °C is compressed isothermally. Does it go through…

## Answer the following questions based on the P-T phase diagram of carbon dioxide: (a) At what temperature and pressure can the solid, liquid and vapour phases of CO2 co-exist in equilibrium? (b) What is the effect of decrease of pressure on the fusion and boiling point of CO2? (c) What are the critical temperature and pressure for CO2? What is their significance? (d) Is CO2 solid, liquid or gas at (a) –70 °C under 1 atm, (b) –60° C under 10 atm, (c) 15 °C under 56 atm? | Learn NCERT solution | Education portal Class 11 Physics | Study online Unit-11 Thermal Properties of Matter

Q.16:- Answer the following questions based on the P–T phase diagram of carbon dioxide: (a) At what temperature and pressure can the solid, liquid and vapour phases of CO2 co-exist in…

## Given below are observations on molar specific heats at room temperature of some common gases. Observations 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 cal/mol K. Explain this difference. What can you infer from the somewhat larger (than the rest) value for chlorine? | Learn NCERT solution | Education portal Class 11 Physics | Study online Unit-11 Thermal Properties of Matter

Q.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…