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• CBSE×
• Class 11 Science×
• Physics×
• Thermal Properties Of Matter×
• Transfer Of Heat By Radiation×

# Transfer Of Heat By Radiation Free Doubts and Solutions

## There are two thin spheres A and B of the same material and same thickness.They emit like black bodies.Radius of A is double that of B.A and B have same tempt. T .When A and B are kept in a room of tempt T0(less than T),the ratio of their rates of cooling (rate of fall of tempt) is

Asked by m.nilu 8th December 2018, 2:03 PM

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## Two bodies A and B have emissivities 0.5 and 0.8 respec .At some tempt the two bodies have emissive powers at these tempt.

Asked by m.nilu 8th December 2018, 1:49 PM

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## Find the ratio of rate of radiations from two solid sphere having ratio of radius 2:1 and ratio of wavelength of radiations of maximum intensity 1:2?   {1} 8:1 {2} 27:1 {3} 64:1 {4} 25:1

Asked by Mamali Nanda 19th July 2016, 9:04 PM

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## 1 gram water is vaporised into steam at 100 degree celsius. The work done against atmosphere is? ( Given density of vapour = 1.65 kg/m3) 1. 39.3J 2. 47.2J 3.29.8J 4.17.9J

Asked by Mamali Nanda 19th July 2016, 8:57 PM

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## IS ther any relation between light and "RADIATION"?  As the velocities of radiation and light are same.

Asked by anjalimishrikotkar 17th January 2016, 1:19 PM

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## Explain why: (i) A body with large reflectivity is a power emitter. (ii) A brass tumbler feels much colder than a wooden tray on a chilly day. (iii) 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 piece in the open, but gives a correct value for the temperature when the same piece is in the furnace. (iv) The earth without its atmosphere would be inhospitably cold. (v) Heating systems based on circulation of steam are more efficient in warming a building than those based on circulation of hot water.

Asked by Topperlearning User 16th April 2015, 9:43 AM

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## Assume that the thermal conductivity of copper is four times that of brass. Two rods of copper and brass, of the same length and cross section are joined end to end. The free end of the copper rod is kept it 0 °C and the free end of the brass rod at 100 °C. Calculate the temperature at the junction of the two rods at equilibrium. Ignore radiation losses.

Asked by Topperlearning User 16th April 2015, 9:40 AM

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## What is thermal conductivity of a perfect heat conductor and a perfect heat insulator?

Asked by Topperlearning User 16th April 2015, 9:37 AM

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## Find the thermal conductivity of metal of a rod of length 0.5 m and diameter 4 cm. One end of the rod is at 110 °C and the other end is in ice at 0 °C. 15 g of ice melts per minute. (latent heat of ice is 80 cal/ g).

Asked by Topperlearning User 16th April 2015, 9:32 AM

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## Two Pizzas one at 100 °C and another at 30 °C are kept on a table. Which one would cool off faster and by how many times? Temperature of surroundings is 20 °C.

Asked by Topperlearning User 16th April 2015, 9:27 AM

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## A wooden plank of 0.025 m is attached to an insulation of 0.075 m. The temperature inside it is 25 ˚C and the outside temperature is 4 ˚C. T is the interface temperature. Take: K(wood)= 0.80 J/s m ˚C, K(insulation)= 0.20 J/s m ˚C. Calculate how much heat energy flows through the wall per second?

Asked by Topperlearning User 15th April 2015, 4:54 PM

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## What are thermal radiations? Give some of its basic characteristics.

Asked by Topperlearning User 15th April 2015, 4:45 PM

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## If a liquid is heated from top, then by which mode the transfer of heat would take place?

Asked by Topperlearning User 15th April 2015, 4:41 PM

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## One thermometer is placed half metre above the tip of the fire and one thermometer is placed half metre at the side of the fire. Would the readings of the two thermometers be same or different and why?

Asked by Topperlearning User 15th April 2015, 4:38 PM

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## Which of the three modes of transfer of heat is the fastest?

Asked by Topperlearning User 15th April 2015, 4:32 PM

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## Explain the working of room heater. How can we increase the efficiency of convections in radiator of a room heater?

Asked by Topperlearning User 15th April 2015, 4:28 PM

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## Why is a new quilt warmer than an old quilt?

Asked by Topperlearning User 4th June 2014, 1:23 PM

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## By what mode of heat transfer is mercury heated?

Asked by Topperlearning User 4th June 2014, 1:23 PM