Question

A metal ball of surface area $200 \mathrm {~cm} ^ { 2 }$ and temperature $527 ^ { \circ } \mathrm { C }$ is surrounded by a vessel at $27 ^ { \circ } \mathrm { C }$ . If the emissivity of the metal is 0.4, then the rate of loss of heat from the ball is

• A. 108 joules approx.
• B. 168 joules approx.
• C. 182 joules approx.
• D. 192 joules approx.

Answer 1

Answer: (C)

182 joules approx.

Answer 2

Rate of heat loss $E = \sigma e A \left( T ^ { 4 } - T _ { 0 } ^ { 4 } \right)$

$= 5.67 \times 10 ^ { - 8 } \times 0.4 \times 200 \times 10 ^ { - 4 }$ ×$\left[ ( 273 + 527 ) ^ { 4 } - ( 273 + 27 ) ^ { 4 } \right]$

$= 5.67 \times 10 ^ { - 8 } \times 0.4 \times 200 \times 10 ^ { - 4 }$ × $( 800 ) ^ { 4 } - ( 300 ) ^ { 4 }$ =182J/sec