Consider a light bulb, in empty space, radiating 200. watts with ...

[mydiamond]

Consider a light bulb, in empty space, radiating 200. watts with its filament heated to 2800.C. Assuming it is a good approximation to a black body.
 
  (a) What is the area of the filament?
  (b) If placed in an oven, with walls at 800.C, what is its net power radiated now?

Question 2

Explain how the eye and a camera differ in adjusting for a change in focus.
 
  What will be an ideal response?

[Liamb2179]

Answer to Question 1

(a) 39.6 mm2
(b) 197. watts

Answer to Question 2

The camera lens has a fixed focal length so it adjusts focus by varying the lens-film distance. The eye has an essentially fixed lens-retina distance so the focal length of the lens is varied by changing the lens curvature (by muscular action).