Tag: perfectly black body

Questions Related to perfectly black body

The coefficient of transmission for an ideal black body is :

physics energy production perfectly black body black-body radiation black body radiation

  1. infinity

  2. zero

  3. 1

  4. more than one

Show answer
Correct Option: B
Explanation:

Ideal black body absorbs all the radiation, no transmission, no reflection.

Out of the following, which body is not an ideal black body?

physics energy production perfectly black body black-body radiation black body radiation

  1. Wein's black body

  2. Ferry's black body

  3. coal

  4. sun

Show answer
Correct Option: C
Explanation:

wein's and ferry's black bodies are well defined in there papers and sun can also be considered as black body because it is very good emitter. but coal is just a normal carbon compound and neither is it a good absorber or emmiter

Read the following statements carefully
(A) Black body radiation is white
(B) Emissivity of a body is equal to its absorptive power
Mark correct option:

physics energy production perfectly black body black-body radiation black body radiation

  1. Statement (A) is correct

  2. Statement (B) is correct

  3. Both are correct

  4. Both are wrong

Show answer
Correct Option: C
Explanation:
  • (A) The combination of radiation of all the visible wavelengths makes white light. Hence black  body radiation is white

(B) Emissivity of body is equal to it's absorptive power, it is not less then absorptive power or greater than absorptive power
  • Hence both the statements are true
  • Hence option C is the right answer
           

The absorptivity of Lamp black is:

physics energy production perfectly black body black-body radiation black body radiation

  1. 0.91

  2. 0.98

  3. 1.00

  4. 0.99

Show answer
Correct Option: C
Explanation:

Black body is a body which absorbs and emit all types of radiations completely. Since we know that lamp black is perfect black body so its absorptivity is $1.00$

Black body spectrum is

physics energy production perfectly black body black-body radiation black body radiation

  1. continuous absorption

  2. line absorption

  3. continuous emission

  4. line emission

Show answer
Correct Option: C
Explanation:

Black Body radiation involves emission of a number of wavelengths, which by definition is continuous emission.

Stefan-Boltzmanns Law for a perfect black body is represented by

physics energy production perfectly black body black-body radiation black body radiation

  1. $\dfrac{dQ}{dt} = \sigma AT^2 $

  2. $\dfrac{dQ}{dt} = \sigma AT^3 $

  3. $\dfrac{dQ}{dt} = \sigma AT^4 $

  4. $ Q = \sigma AT^4 $

Show answer
Correct Option: C
Explanation:
Stefan boltzmann's law, $\Rightarrow \cfrac { dQ }{ dt } =\sigma A\varepsilon { T }^{ 4 }$
( for black body, $\varepsilon=1$)
So, for black body stefan's boltzmann's law is $\Rightarrow \cfrac { dQ }{ dt } =\sigma A { T }^{ 4 }$
Stefan's boltzmann's law states that total energy radiated from a surface is proportional to the forth power of its absolute temperature.

Ferry's black body is accurately represented by 

physics energy production perfectly black body black-body radiation black body radiation

  1. A fine hole in a double walled spherical cavity.

  2. A fine hole in a double walled spherical cavity, evacuated and painted black.

  3. A fine hole in a spherical cavity, evacuated and painted black.

  4. A fine hole in a black cavity.

Show answer
Correct Option: B
Explanation:

Ferry's black body is accurately represented by a fine hole in a double walled spherical cavity, evacuated and painted black.

$\rightarrow$ Ferry designed the simplest black body. It is a double walled evacuated spherical cavity whose inner wall is blackened. The space between wall is evacuated to prevent heat loss by conduction and radiation. There is a fine hole in it. All the radiations incident upon this hole are absorbed by this black body. 

Ferry's black body is 

physics energy production perfectly black body black-body radiation black body radiation

  1. a perfect reflector of heat.

  2. perfectly black.

  3. platinum black.

  4. almost perfectly black.

Show answer
Correct Option: D
Explanation:
Ferry's black body is almost perfectly black.
As because emission of heat and absroption of heat takes place completely.

Black body radiation is

physics energy production perfectly black body black-body radiation black body radiation

  1. White

  2. IR

  3. Black

  4. UV

Show answer
Correct Option: A
Explanation:

a black body looks black because it absorbs light of all colors. so when it radiates energy as light, it will release all the colors which it had absorbed resulting in the emission of white light, because white light is the resultant of many component colors.

The original temperature of a black body is $727^\circ C$. Calculate temperature at which total radiant energy from this black body becomes double:

physics energy production perfectly black body black-body radiation black body radiation

  1. $971K$

  2. $1189K$

  3. $2001K$

  4. $1458K$

Show answer
Correct Option: B
Explanation:

$Rediant Energy = \sigma T^2$

$Energy = \sigma (1000)^4$
$E _2 = 2 E _1$
$Then$
$\sigma T _2 ^{4} = 2 \times \sigma (1000)^4$
$T _2 = 2^\frac{1}{4} \times1000$
$T _2 = 1189 K$