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Explain Why A Body with Large Reflectivity is a Poor Emitter

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प्रश्न

Explain why a body with large reflectivity is a poor emitter

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उत्तर १

According to Kirchh off’s law of black body radiations, good emitters are good absorbers and bad emitters are bad absorbers. A body with large reflectivity is a poor absorber of heat and consequently, it is also a poor emitter.

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उत्तर २

A body with a large reflectivity is a poor absorber of light radiations. A poor absorber will in turn be a poor emitter of radiations. Hence, a body with a large reflectivity is a poor emitter.

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अध्याय 10: Thermal Properties of Matter - Exercises [पृष्ठ २९७]

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एनसीईआरटी Physics Part 1 and 2 [English] Class 11
अध्याय 10 Thermal Properties of Matter
Exercises | Q 21.1 | पृष्ठ २९७

संबंधित प्रश्न

A copper block of mass 2.5 kg is heated in a furnace to a temperature of 500 °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 J g–1 K–1; heat of fusion of water = 335 J g–1).


Answer the following questions based on the P–T phase diagram of CO2:

What happens when CO2 at 4 atm pressure is cooled from room temperature at constant pressure?


Answer the following questions based on the P–T phase diagram of CO2:

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.


Answer the following questions based on the P–T phase diagram of CO2:

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.


Answer the following questions based on the P–T phase diagram of CO2:

CO2 is heated to a temperature 70 °C and compressed isothermally. What changes in its properties do you expect to observe?


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 coefficient of thermal conductivity of thermacole is 0.01 J s–1 m–1 K–1. [Heat of fusion of water = 335 × 103 J kg–1]


A metal block of heat capacity 80 J°C−1 placed in a room at 20°C is heated electrically. The heater is switched off when the temperature reaches 30°C. The temperature of the block rises at the rate of 2°C s−1 just after the heater is switched on and falls at the rate of 0.2°C s−1 just after the heater is switched off. Assume Newton's law of cooling to hold. 

  1. Find the power of the heater. 
  2. Find the power radiated by the block just after the heater is switched off. 
  3. Find the power radiated by the block when the temperature of the block is 25°C.
  4. Assuming that the power radiated at 25°C represents the average value in the heating process, find the time for which the heater was kept on.

Answer the following question based on the P-T phase diagram of carbon dioxide:

What is the effect of decrease of pressure on the fusion and boiling point of CO2?


Answer the following question based on the P-T phase diagram of carbon dioxide:

What are the critical temperature and pressure for CO2? What is their significance?


100 g of water is supercooled to –10°C. At this point, due to some disturbance mechanised or otherwise some of it suddenly freezes to ice. What will be the temperature of the resultant mixture and how much mass would freeze?

`[S_w = 1cal/g/^circC and L_(Fusion)^w = 80cal/g]`


Latent heat of a substance is best defined as ______.


Relation between heat Q, mass mmm, and specific latent heat L ______.


Effect of increasing external pressure on boiling point ______.


In a heating curve of ice and water, which part represents the latent heat of fusion?


Why is the latent heat of vaporisation much greater than the latent heat of fusion?


The heating curve below shows temperature vs. heat added for ice, water and steam at 1 atm ______.


For 1 kg of water, which phase change requires more energy?


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