Radiation Questions: Paper – 01

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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)


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)


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)





Answer: (b)


Two stars A and B radiate maximum energy at 3600°A and 3600°A 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)


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)


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)


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)


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)


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)


A metal piece heated to T1 °K. The temperature of the surrounding is T2°K. 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)


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)


A body in a room cools from 90°C to 80°C in 5 minutes. the time taken to cool from 70°C to 60°C 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)


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 3000°K, which of these will cool fastest? (MNR 83)

(a) Sphere

(b) Cube

(c) Plate

(d) None

Answer: (c)


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 (MNR 87)

(a) 1.36 times

(b) 2.36 times

(c) 3.36 times

(d) 4.36 times

Answer: (a)


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. (MP-PMT-95, MHT-CET 2002)

(a) 50 sec

(b) 90 sec

(c) 60 sec

(d) 30 sec

Answer: (a)


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)


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 (PMT-MP 90)

(a) 200°C

(b) 200°K

(c) 800°C

(d) 800°K

Answer: (d)


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)


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 1

(c) a + r = -t

(d) a ≠ r + 1

Answer: (a)


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) 2801°C

Answer: (a)

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)


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)


Which of the following is most repaid process (NCERT 80)

(a) Conduction

(b) Convection

(c) Radiation

(d) None of these

Answer: (c)


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)

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