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Q. No.
Given below are two statements: 
Assertion (A): The earth without its atmosphere would be inhospitably cold.
Reason (R): All heat would escape in the absence of the atmosphere.
 
1. Both (A) and (R) are true and (R) is the correct explanation of (A).
2. Both (A) and (R) are true but (R) is not the correct explanation of (A).
3. (A) is true but (R) is false.
4. Both (A) and (R) are false.


 
Subtopic:  Radiation |
 91%
Level 1: 80%+
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The temperature of the surface of the Sun is nearly \(6000~\text{K}\) and the amount of total energy emitted by the Sun per second is \(4\times10^{26}~\text{J}.\) If the temperature of the surface of the Sun is \(18000~\text{K},\) then the amount of thermal radiation emitted by the same will be:
1. \(3.24\times10^{28}~\text{W}\) 
2. \(2.52\times10^{28}~\text{W}\) 
3. \(8\times10^{26}~\text{W}\) 
4. \(16\times10^{27}~\text{W}\) 

Subtopic:  Radiation |
 84%
Level 1: 80%+
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The emissivity of a body is given by    \(e={\Large\frac{1}{3}}\bigg(1+{\Large\frac{T}{400}}\bigg),\) where \(T\) is the absolute temperature of the body in the range:    \(200~\text K\leq T​ \leq800~\text K\)
When the temperature of the body increases from \(200~\text K\) to \(500~\text K,\) its emissivity:
1. decreases from \(\dfrac12\) to \(\dfrac14\)
2. increases from \(\dfrac12\) to \(\dfrac34\)
3. decreases from \(\dfrac12\) to \(\dfrac13\)
4. increases from \(\Large\frac12\) to \(\Large\frac23\)
Subtopic:  Radiation |
 82%
Level 1: 80%+
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A thermos flask is polished well:
1. to make it attractive
2. for shining
3. to absorb all radiation from outside
4. to reflect all radiation from outside
Subtopic:  Radiation |
 82%
Level 1: 80%+
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A black body of a given surface area at temperature \(T\) emits a certain amount of thermal radiation per second. If the temperature of the black body is doubled, the change of thermal radiation emitted will be:
1. \(2\) times more than the original value.
2. \(16\) times more than the original value.
3. \(\dfrac{1}{16}\) times the original value.
4. \(\dfrac{1}{2}\)times the original value.
Subtopic:  Radiation |
 82%
Level 1: 80%+
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Given below are two statements: 
Assertion (A): A body that is a good radiator is also a good absorber of radiation at a given wavelength.
Reason (R): According to Kirchhoff's law, the absorptivity of a body is equal to its emissivity at a given wavelength.
 
1. Both (A) and (R) are true and (R) is the correct explanation of (A).
2. Both (A) and (R) are true but (R) is not the correct explanation of (A).
3. (A) is true but (R) is false.
4. Both (A) and (R) are false.


 
Subtopic:  Radiation |
 79%
Level 2: 60%+
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A spherical black body with a radius of \(12~\text{cm}\) radiates \(450~\text W\) power at \(500~\text K.\) If the radius were halved and the temperature is doubled, the power radiated in watts would be:
1. \(450\)
2. \(1000\)
3. \(1800\)
4. \(225\)

Subtopic:  Radiation |
 76%
Level 2: 60%+
NEET - 2017
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Two bodies A and B have thermal emissivities of 0.01 and 0.81 respectively. The outer surface areas of the two bodies are the same. The two bodies emit total radiant power at the same rate. The wavelength λB of B corresponding to maximum spectral radiancy in the radiation differs from that of A by 1.00 µm. If the temperature of A is 5802 K:

1. the temperature of B is 17406 K.

2. λB = 1.5 µm

3. the temperature of B is 11604 K.

4. the temperature of B is 2901 K.

Subtopic:  Radiation |
 76%
Level 2: 60%+
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If the absolute temperature of a star doubles but its radius halves, then the rate of radiation from the star:
1. increases \(4\) times
2. increases \(2\) times
3. remains unchanged
4. decreases \(2\) times
Subtopic:  Radiation |
 76%
Level 2: 60%+
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