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1. 512 calories of radiation is incident on a body. It absorbs 220 calories the coefficient of emission is (MHT-CET 2001) (a) 0.43 (b) 0.57 (c) 1.7 (d) 0.34 Answer: (b) 2. Heat energy received by the earth from the sun is due to (CPMT 1994) (a) Convection (b) Radiation (c) Reflection of light (d) Transmission of light Answer: (b) 3. Two sphere of same material have radii r 1 and r 2 . they are heated to same temperature and kept in same enclosure at low temperature their rates of loss of heat are in the ratio (JIPMER 98) (a) (b) (c) (d) Answer: (b) 4. Two stars A and B radiate maximum energy at 3600A and 3600A respectively. Then the ratio of absolute temperatures of A and B is (P.M.T. MP 91) (a) 256: 81 (b) 81: 256 (c) 3: 4 (d) 4: 3 Answer: (d) 5. Emissivity of perfectly black body is (MHT-CET 2003) (a) 1 (b) 2 (c) 5 (d) 0 Answer: (a) 6. Absorptive power of perfectly black body is (PMT- 89) (a) Zero (b) Infinity (c) One Answer: (c)

radiation.docx

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1. 512 calories of radiation is incident on a body. It absorbs 220 calories the coefficient of emission is (MHT-CET 2001)(a) 0.43(b) 0.57(c) 1.7(d) 0.34

Answer: (b)

2. Heat energy received by the earth from the sun is due to (CPMT 1994)(a) Convection(b) Radiation(c) Reflection of light(d) Transmission of light

Answer: (b)

3. Two sphere of same material have radii r1 and r2. they are heated to same temperature and kept in same enclosure at low temperature their rates of loss of heat are in the ratio (JIPMER 98)

(a) 

(b) 

(c) 

(d) 

Answer: (b)

4. Two stars A and B radiate maximum energy at 3600A and 3600A respectively. Then the ratio of absolute temperatures of A and B is (P.M.T. MP 91)(a) 256: 81(b) 81: 256(c) 3: 4(d) 4: 3

Answer: (d)

5. Emissivity of perfectly black body is (MHT-CET 2003)(a) 1(b) 2(c) 5(d) 0

Answer: (a)

6. Absorptive power of perfectly black body is  (PMT-89)(a) Zero(b) Infinity(c) One(d) Constant

Answer: (c)

7. Newton’s law of cooling is also applicable to (NCERT)(a) Convection losses(b) Natural convection losses(c) Forced convection losses(d) None of the above

Answer: (c)

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8. Which of the following statement is wrong?(NCERT 76)(a) Rough surfaces are better radiators tan smooth surfaces(b) Highly polished mirror surfaces are very good radiators(c) Black surfaces are better absorbers then white ones(d) Black surfaces are better radiators then white ones

Answer: (b)

9. The best ideal black body is (CPMT-86)(a) Lamp of charcoal heated to high temperature(b) Metal coated with a black dye(c) Glass surface coated with coalter(d) Hollow enclosure blackened inside and having a small

hole

Answer: (d)

10. The earth intercepts approximately one billionth of the power radiated by the sun. if the surface temperature of the sun were to drop by a factor of 2, the average radiant energy incident on earth per second would reduce by factor of (MHT-CET 2001)(a) 2(b) 4(c) 8(d) 16

Answer: (d)

11. A metal piece heated to T1 K. The temperature of the surrounding is T2K. the heat in the surrounding due to radiation is proportional to (NCERT 72)(a) (T14  T24)(b) (T1  T2)4

(c) (T14  T24)(d) (T13  T23)

Answer: (a)

12. If the temperature of the sun is doubled. The rate of energy received on the earth will be increased by a factor of (CBSE-93,94)(a) 2(b) 4(c) 8(d) 16

Answer: (d)

13. A body in a room cools from 90C to 80C in 5 minutes. the time taken to cool from 70C to 60C is (CPMT 92)(a) Less than 5 minute(b) 5 minute(c) More than 5 minutes (d) Less or more than 5 minutes depending upon the nature

of the body

Answer: (c)

14. A sphere, a cube and a thin circular plate, all made of the same material and having the same mass are initially heated to a temperature of 3000K, which of these will cool fastest? (MNR 83)(a) Sphere(b) Cube(c) Plate(d) None

Answer: (c)

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15. The temperature of a piece of metal is raised from 27C to 51.2C. the rate at which metal radiates energy increases nearly (MNR 87)(a) 1.36 times(b) 2.36 times(c) 3.36 times(d) 4.36 times

Answer: (a)

16. A cup of tea cools from 80C to 60C in one minute. The ambient temperature is 30C. in cooling from 60C to 50C, it will take. (MP-PMT-95, MHT-CET 2002)(a) 50 sec(b) 90 sec(c) 60 sec(d) 30 sec

Answer: (a)

17. Spectrum of a perfectly black body is(MP PMT-89, MHT-CET 2005)(a) Line spectrum(b) Band spectrum(c) Continuous spectrum(d) None of these

Answer: (c)

18. An object is at the temperature of 400C. at what temperature would it radiant energy twice as first? The temperature of surrounding may be assumed to be negligible (PMT-MP 90)(a) 200C(b) 200K(c) 800C(d) 800K

Answer: (d)

19. A body at high temperature T K radiates heat at rate proportional to(MHT CET 2001)(a) T4

(b) T4

(c) T(d) T2

Answer: (a)

20. Co-efficient of reflection, coefficient of absorption and coefficient transmission are related as(MHT-CET 2005)(a) a  r  1  1(b) a  r  t  1(c) a  r  t(d) a  r  1

Answer: (a)

21. The earth receives at its surface radiation from the sun at the rate of 1400 W/m2. the distance of the centre of the sun from the surface of the earth is 1.5  1011 m and the radius of the sun is 7.0  108 m. treating sun as a black body, it follows from the above data that its surface temperature is,(I.I.T 89)(a) 5801 K(b) 106 K(c) 50.1 K(d) 2801C

Answer: (a)

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22. The process of heat transfer in which heat is transferred with actual migration of medium particles is known as(AFMC-94)(a) Conduction(b) Convection(c) Radiation(d) Reflection

Answer: (b)

23. A black body is at a temperature of 500K. it emits energy at a rate which is proportional to (CBSE 97)(a) 500(b) (500)2

(c) (500)3

(d) (500)4

Answer: (d)

24. Which of the following is most repaid process(NCERT 80)(a) Conduction(b) Convection(c) Radiation(d) None of these

Answer: (c)

25. The wavelength of maximum energy released during an atomic explosion was 2.93  1010m. the maximum temperature attained must be(Wien’s constant  2.93  103mK) (MHT-CET 2002)(a) 5.86  107 K(b) 1013 K(c) 107 K(d) 107 K

Answer: (d)

 

1. If a  0.72, r  0.24, then the value of t is(MHT-CET 2003)(a) 0.02(b) 0.04(c) 0.4(d) 0.2

Answer: (b)

2. A body cools from 50C to 46C in 5 minutes and to 40C in the next 10 minutes. The surrounding temperature is (MHT-CET-1999)(a) 30C(b) 28C(c) 36C(d) 32C

Answer: (a)

3. According to Wien’s law (PMT MP 88)(a) m T  constant

(b)  constant

(c)  constant

Answer: (a)

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(d) T  m  constant4. A black body is at 300 K. it emits energy at a rate which is

proportional to (AIMS-2002)(a) (300)(b) (300)2

(c) (300)4

(d) (300)3

Answer: (c)

5. Which of the following will radiate heat to large extent?(MNR-92)(a) Rough surface(b) Polished surface(c) Black rough surface(d) Black polished surface

Answer: (c)

6. The rate of radiation of black body at 0C is E watt. The n the rate of radiation of this black body at 273C will be (MP-PMT 89)(a) 16 E(b) 8 E(c) 4 E(d) E

Answer: (a)

7. A black body radiates energy at the rate of E watt m2 at a temperature of T Kelvin. When the temperature is reduced to T/2 Kelvin, the radiant energy will become(MPPMT 92, CPMT 88, MNR 93)

(a) 

(b) 

(c) (d) None of the above

Answer: (c)

8. Woolen clothes keep the body warm, because wool(EAMCET 78, AIMS 98)(a) Is a bad conductor(b) Increases the temperature of body(c) Decreases the temperature(d) All of these

Answer: (a)

9. The good absorber of heat are (PMT 89)(a) Non-emitter(b) Poor-emitter(c) Good-emitter(d) Highly polished

Answer: (c)

10. The maximum energy in the thermal radiation from a hot source occurs at a wavelength of 11  105 cm. according to Wien’s law, the temperature of the source (on Kelvin scale) will be n times the temperature of another source on (Kelvin scale) for which the wavelength at a maximum energy is

Answer: (a)

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5.5  105 cm. The value of n is(CPMT 91)(a) 2(b) 4(c) 1/2(d) 1

11. Two sphere of the same material have radii 1 m and 4 m and temperature 4000 K and 2000 K respectively. the energy radiated per second by the first sphere is(I.I.T 88)(a) Greater then by the second (b) Less than that by the second(c) Equal in both cases(d) The information is incomplete to draw and conclusion

Answer: (c)

12. A surface at temperature T0 K receives power P by radiation from a small sphere at temperature T  T0 and at a distance d. if both T and d are doubled, the power received by surface will becomes approximately(NSEP 89)(a) P(b) 2 P(c) 4 P(d) 16 P

Answer: (c)

13. If temperature of a black body increases from 7C to 287C, then the rate of energy radiation becomes(HARYANA PMT-2000)

(a) (b) 16 times(c) 4 times(d) 2 times

Answer: (b)

14. A bucket full of hot water is kept in a room and it cools from 75C to 70C in t1 minutes from 70C to 65C in t2 minutes and from 65C to 60C in t3 minutes; then(NCERT 80, CBSE 95, MHT-CET 99)(a) t1  t2  t3(b) t1  t2  t3(c) t1  t2  t3(d) t1  t2  t3

Answer: (b)

15. The velocity with which thermal radiation travels in vacuum is(EAMCET-82)(a) 3  106 m/s(b) 3  107 m/s(c) 3  108 m/s(d) 3  1016 m/s

Answer: (c)

16. In which process the rate of transfer of heat is maximum? (CMEE 94)(a) Conduction(b) Convection(c) Radiation(d) In all these heat is transferred with the same velocity

Answer: (c)

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17. A body cools from 60C to 50C in 10 minutes. If the room temperature is 25C and assuming Newton’s law of cooling to hold good, the temperature of the body at the end of the next 10 minutes will be (MP-PMT 98)(a) 38.5C(b) 40C(c) 42.85C(d) 45C

Answer: (c)

18. Two spheres made of same material have radii in the ratio 2:1. if both the spheres are at same temperature, then what is the ratio of heat radiation energy emitted per second by them? (MHT-CET 2004)(a) 1: 4(b) 4: 1(c) 3: 4(d) 4: 3

Answer: (b)

19. Solar radiation emitted by sun resembles that emitted by a black body at a temperature of 6000 K. maximum intensity is emitted at a wavelength of about 4800 A. if the sun were cooled down from 6000 K to 3000 K, then the peak intensity would occur at a wavelength of(PMT MP 91)(a) 4800 A(b) 9600 A(c) 2400 A(d) 19200 A

Answer: (b)

20. A perfectly black body emits radiation at temperature T1 K. if it sis to radiate 16 times this power, its temperature T2. will be (BHU 94)(a) T2  16 T1(b) T2  8 T1(c) T1  4 T1(d) T2  2 T1

Answer: (d)

21. Unit of Stefan’s constant is given by (MHT-CET 2006)(a) W/ m K2

(b) W/ m2 K2

(c) W2/ m2 K4

(d) W/ mK

Answer: (b)

22. A black body at hot temperature at 227C radiates heat at a rate of 5 cal/cm2 s. at a temperature of 727C the rate of heat radiated per unit area will be(MHT-CET 2002)(a) 50 cal/cm2 s(b) 250 cal/cm2 s(c) 80 cal/cm2 s(d) 100 cal/cm2 s

Answer: (c)

23. According to Kirchhoff’s law of radiation which of the following relation is correct (MHT CET 2006)(a) Eb  Ea

Answer: (b)

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(b) (c) Eb  E2a(d) Eb  E  a

24. A person with dark skin as compared to a person with white skin will experience (CPMT-88)(a) Less heat and less cold(b) More heat and more cold(c) More heat and less cold(d) Less heat and more cold.

Answer: (b)

25. For which of the following process, the thermal conduction is maximum? (AFMC PUNE-2002)(a) Combustion(b) Radiation(c) Convection(d) Conduction