1. A blackened solid copper sphere with radius of 0.02m is placed in an evacuated enclosure with...

1. A blackened solid copper sphere with radius of 0.02m is placed in an evacuated enclosure with walls kept at 100°C. In what time does its temperature change from

2 .The operating temperature of a tungsten filament in an incandescent lamp is 2460 K, and its total emissivity is 0.30. Find the surface area of the filament of a 100-W lamp.