Question

The filament of a light bulb is cylindrical with length 1 = 20 mm and radius r = 0.05 mm. The filament is maintained at a temperature T = 5000 K by an electric current. The filament behaves approximately as a black body, emitting radiation isotropically. At night, you observe the light bulb from a distance D = 10 km with the pupil of your eye fully dilated to a radius r = 3 mm. (a) What is the total power radiated by the filament? (b) How much radiation power enters your eye?

Answer 1

quier, l = 20mm z = dos m 5000 K = 0.020m = 5x10-5 m Also, the filament behaves lits a black bedu аррциоіng L (o, u Cou toku e the emissively I to be nearly 1. ellsing stefan's Law , kamer radiated by the filament is quien by the formula P = TACP9 0-5.67X10 W/m Ka Slefan's wrist ant A = Tufan cua of the objet e = emissively - Temperature in ( Keluin scale) So for the cylindrical filament A = air I +2582 - 16.283 X0 + 1.57 810-8 m² = 6.298 x 10 m²

- P = 6.298x10 6 x 1x 5.678108 X (5000) = 223.21 (Ils 2 P = 223.21 watt @