Radiation Questions: Paper – 03

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The flow of heat from a hot body to a cold body is an example of (MHT-CET-2001)

(a) Isothermal process

(b) Reversible process

(c) Adiabatic process

(d) Irreversible process

Answer: (d)


Three black bodies A, B and C in the form of cubes of sides in the ratio of 3: 4: 5 are kept at the same high temperature. The ratio of the quantity of heat lost per second by A, B and C will be

(a) 27: 64: 125

(b) 5: 4: 3

(c) 9: 16: 25

(d) 25: 16: 9

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 300°C. which one of these cools faster?

(a) Circular plate

(b) Sphere

(c) Cube

(d) All will cool at the same rate

Answer: (a)


The emissive of a perfectly black body is

(a) 0

(b) 0.5

(c) 1

(d) 0.75

Answer: (c)


If the wavelengths of maximum intensity of radiation emitted by the moon and the sun are 104 m and 0.5 × 106m respectively, then the ratio of their temperature is

(a) 200

(b) 100



Answer: (c)


The coefficient of transmission of a perfectly black body is

(a) Zero

(b) One

(c) 0.5

(d) 0.75

Answer: (a)


When a black body is heated, it emits heat radiations of

(a) Infrared wavelengths

(b) Ultraviolet wavelengths

(c) All wavelengths

(d) A particular wavelengths

Answer: (c)


An ideal black body is represented by

(a) A metal coated with a black dye

(b) A glass surface coated with coal tar

(c) A hollow enclosure blackened from inside and having a small hole

(d) A lump of charcoal heated to a high temperature

Answer: (c)


The temperature of a furnace is 2327°C and the intensity is maximum in its radiation spectrum at 1200. If the intensity in the spectrum of a star is maximum at 4800, then the surface temperature of the star is

(a) 6500 K

(b) 6000 K

(c) 4800 K

(d) 7500 K

Answer: (a)


The coefficient of transmission and coefficient of reflection for a given body at a given temperature are 0.33 and 0.64 respectively. Then the coefficient of emission of the same body at the same temperature will be

(a) 0.3

(b) 0.003

(c) 0.03

(d) 0.33

Answer: (c)


The correct equation out of the following is (MHT-CET-2006)





Answer: (b)


The maximum wavelength of radiation emitted by a black body at 1227°C is λm. What is its maximum wavelength at 2227°C?





Answer: (c)


According to Prevost’s theory of heat exchange, the heat exchange shops at (MHT-CET-2007)

(a) 0°C

(b) – 5°C

(c) – 273°C

(d) – 273 K

Answer: (c)


The rate of cooling of a body is 0.5°C/minute, when the body is 50°C above the surrounding. What is the rate of cooling if the body is 30°C above the surrounding?

(a) 24°C/hour

(b) 18°C/hour

(c) 30°C/hour

(d) 12°C/hour

Answer: (b)


Coefficient of transmission and coefficient of reflection for a given body are 0.22 and 0.74 respectively. Then, at a given temperature, the coefficient of emission for the body is (MHT-CET-2005)

(a) 0.4

(b) 0.04

(c) 0.96

(d) 0.22

Answer: (b)


If a black body is heated from 27°C to 927°C, then the ratio of the radiation emitted by the body at the two temperatures will be

(a) 1: 4

(b) 1: 16

(c) 1: 256

(d) 1: 64

Answer: (c)


A body cools from 100°C to 70°C in 8 minutes. If the room temperature is 15°C and assuming Newton’s law of cooling holds good, then time required for the body to cool from 70°C to 40°C is (MHT-CET-2005)

(a) 14 s

(b) 10 s

(c) 8 s

(d) 5 s

Answer: (a)


A body radiates heat at the rate of 4 cal/m2/s, when its temperature is 227°C. what is the heat radiated by the same body when its temperature is 727°C?

(a) 8 cal/m2/s

(b) 16 cal/m2/s

(c) 64 cal/m2/s

(d) 32 cal/m2/s

Answer: (c)


Two thermometers A and B exposed to sunlight. The value of A is painted black but that of B is not painted. The correct statement regarding this case is


(a) Temperature of B will rise faster

(b) Temperature of A will remain more than B

(c) Both of A and B show equal rise from the beginning

(d) Temperature of A will rise faster than B but the final temperature will be same in both

Answer: (d)


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)


The temperature of a black body is gradually increased. The colour of the body will change from

(a) White-green-red

(b) Red-yellow-blue

(c) Red-violet-yellow

(d) Yellow-green-red

Answer: (b)


Radiation emitted by a surface is directly proportional to (MHT-CET-2000)

(a) Third power of its temperature

(b) Equal to its temperature

(c) Twice power of its temperature

(d) Fourth power of its temperature

Answer: (d)


The coefficient of absorption of perfectly black body is


(a) 1

(b) 0

(c) 0.75

(d) None of these

Answer: (a)


Two bodies A and B at temperatures T1 K and T2 K respectively have the same dimensions. Their emissivities are in the ratio of 1: 3. if they radiate the same amount of heat per unit time, then the relation between their temperatures is given by





Answer: (c)


A body radiates heat at the ate of 5 cal/m2-s when its temperature is 227°C. the heat radiated by the same body when its temperature is 727°C is


(a) 10 cal/m2-s

(b) 20 cal/m2-s

(c) 40 cal/m2-s

(d) 80 cal/m2-s

Answer: (d)

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