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Kirchoff's Law

The emissive ...

Question

The emissive power of a black body at $T = 300 K$ is $100 W a t t / m^{2}$ . Consider a body $B$ of area $A = 10 m^{2}$ , coefficient of reflectivity $r = 0.3$ and coefficient of transmission $t = 0.5 .$ Its temperature is $300 K$ . Then which of the following is/are correct

The emissive power of

B

20 W / m^{2}

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The emissive power of

B

200 W / m^{2}

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The power emitted by

B

200 W

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The emissivity of

B

= 0.2

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Solution

The correct options are
A The emissive power of $B$ is $20 W / m^{2}$
C The power emitted by $B$ is $200 W$
D The emissivity of $B$ is $= 0.2$
We know that $a = (1 - r - t) = 0.2$ (for the body $B$ )
Since, $ϵ = a$
$⟹ ϵ = 0.2$
$∴ E = E_{b} ϵ = (100) (0.2) = 20 W / m^{2}$
Power emitted = Area $\times$ $E$ = $20 \times 10 = 200$ $W$

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Similar questions

Q. The emissive power of a blackbody at

T = 300 K

100 W / m^{2}

. Consider a body B of area

A = 10 m^{2}

coefficient of reflectivity

r = 0.3

and coefficient of transmission

t = 0.5

. Its temperature is

300 K

. Then which of the following is correct?

Q. The emissive power of a black body at

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100 {W/m}^{2}

. Consider a body

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, coefficient of reflectivity

r = 0.3

and coefficient of transmission

t = 0.5

. Its temperature is

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T = 300 K

100 W a t t / m^{2}

. Consider a body

B

of area

A = 10 m^{2}

, coefficient of reflectivity

r = 0.3

and coefficient of transmission

t = 0.5 .

Its temperature is

300 K

. Then which of the following is/are correct

Q. If the emissive and absorptive powers of a body are

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and

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respectively at temperature

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then emissive power of a black body will be

Q. The energy radiated by a black body at

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The emissive power of a black body at T=300 K is 100 Watt/m2. Consider a body B of area A=10 m2, coefficient of reflectivity r=0.3 and coefficient of transmission t=0.5. Its temperature is 300 K. Then which of the following is/are correct

The correct options are A The emissive power of B is 20 W/m2 C The power emitted by B is 200 W D The emissivity of B is =0.2 We know that a=(1−r−t)=0.2 (for the body B ) Since, ϵ=a ⟹ϵ=0.2 ∴E=Ebϵ=(100)(0.2)=20W/m2 Power emitted = Area × E = 20×10=200 W

The emissive power of a black body at $T = 300 K$ is $100 W a t t / m^{2}$ . Consider a body $B$ of area $A = 10 m^{2}$ , coefficient of reflectivity $r = 0.3$ and coefficient of transmission $t = 0.5 .$ Its temperature is $300 K$ . Then which of the following is/are correct