UPSC  Physics

31. The temperature of a piece of metal is raised from 27°C to 51.2°C. the rate at which metal radiates energy increases nearly

1.36 times 2.36 times 3.36 times 4.36 times

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32. A cup of tea cools from 80°C to 60°C in one minute. The ambient temperature is 30°C. in cooling from 60°C to 50°C, it will take

50 sec 90 sec 60 sec 30 sec

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33. Spectrum of a perfectly black body is

Line spectrum Band spectrum Continuous spectrum None of these

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34. An object is at the temperature of 400°C. at what temperature would it radiant energy twice as first? The temperature of surrounding may be assumed to be negligible

200°C 200°K 800°C 800°K

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35. The process of heat transfer in which heat is transferred with actual migration of medium particles is known as

Conduction Convection Radiation Reflection

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36. Which of the following is most repaid process

Conduction Convection Radiation None of these

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37. Which of the following will radiate heat to large extent?

Rough surface Polished surface Black rough surface Black polished surface

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38. The rate of radiation of black body at 0°C is E watt. The n the rate of radiation of this black body at 273°C will be

16 E 8 E 4 E E

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39. Woolen clothes keep the body warm, because wool

Is a bad conductor Increases the temperature of body Decreases the temperature All of these

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40. The good absorber of heat are

Non-emitter Poor-emitter Good-emitter Highly polished

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