Question
A copper ball 2 cm in radius is heated in a furnace to 327 °C. If its emissivity is 0.3, at what rate does it radiate energy?
1.72 W
2.73 W
11.0 W
2.15 W
Solution
C.
11.0 W
The surface area of the ball
A = 4
= (4 ) ( 0.02 m)2
A = 0.05 m2
and its absolute temperature is
T = 327 + 273
T = 600 K
P = e σ AT4
= [ 0.3 × 5.67 × 10-8 × 0.05 × (600)4 ]
P = 11.0 W
