A body at a temperature of 728° C and has surface area 5 cm, radiates 300 J of energy each minute. The emissivity is: (Given: Boltzmann constant =5.67× 10-8 watt m2K4 )

Question

A body at a temperature of 728° C and has surface area 5 cm, radiates 300 J of energy each minute. The emissivity is: (Given: Boltzmann constant =5.67× 10-8 watt m2K4 ) (A)  e=0.18  (B)  e=0.02  (C)  e=0.2  (D)  e=0.15

Tardigrade Admin · Accepted Answer

Q=E A t=e σ(T4-T04) At where t= time T0= temperature of surrounding When, T>T0 Q=e σ T4 At 300=e ×(5.67 × 10-8)(1000)4(5.00 × 10-4) e =0.18

Q. A body at a temperature of $728^{\circ} C$ and has surface area $5 c m$ , radiates $300 J$ of energy each minute. The emissivity is: (Given: Boltzmann constant $= 5.67 \times 10^{- 8}$ watt $m^{2} K^{4}$ )

$e = 0.18$

$e = 0.02$

$e = 0.2$

$e = 0.15$

$Q = E A t = e σ (T^{4} - T_{0}^{4}) A t$
where $t =$ time
$T_{0} =$ temperature of surrounding
When, $T > T_{0}$
$Q = e σ T^{4} A t$
$300 = e \times (5.67 \times 1 0^{- 8}) (1000)^{4} (5.00 \times 1 0^{- 4})$
$e = 0.18$

Q. A body at a temperature of 728∘C and has surface area 5cm, radiates 300J of energy each minute. The emissivity is: (Given: Boltzmann constant =5.67×10−8 watt m2K4 )

e=0.18

e=0.02

e=0.2

e=0.15