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Thermal Properties Of Matter

Question

The temperature of a body is increased from $-$ 73^o C to 327^o C. Then the ratio of emissive power is

1/9

1/27

27

81

Solution

Emissive power is the energy of thermal radiation emitted in all directions per unit time per area of a surface given temperature.

Radiation from a body = R

R = e σ T⁴ × time × area

where e = emissive power

∴ eT⁴ = constant

e = $(\frac{constant}{T^{4}})$

⇒ $\frac{e_{1}}{e_{2}} = {(\frac{T_{2}}{T_{1}})}^{4}$

⇒ $\frac{e_{1}}{e_{2}} = {(\frac{273 + 327}{273 - 73})}^{4}$

⇒ $\frac{e_{1}}{e_{2}} = \frac{{(3)}^{4}}{1}$

⇒ = $\frac{81}{1}$

⇒ $\frac{e_{1}}{e_{2}} = \frac{81}{1}$