The diameter of the Milky Way is 100,000 ly. This distance in SI ...

[burchfield96]

The diameter of the Milky Way is 100,000 ly. This distance in SI units is
 
  A)
 
  5 x 1015 m.
  B)
 
  1 x 1021 m.
  C)
 
  4 x 1030 m.
  D)
 
  3 x 1036 m.
  E)
 
  2 x 1042 m.

Question 2

State how to draw the three rays for finding the image position due to a thin lens.
 
  What will be an ideal response?

[mochi09]

Answer to Question 1

B

Answer to Question 2

Ray 1 leaves the top of the object and is drawn such that it is parallel to the axis; therefore it emerges from the lens along a line through the focal point on the back side of the lens.
Ray 2 leaves the top of the object and is made to pass through the other focal point; therefore it emerges from the lens parallel to the axis.
Ray 3 leaves the top of the object and is directed toward the very center of the lens; therefore it emerges from the lens at the same angle as it entered.

[burchfield96]

Gracias!

[brbarasa]

Excellent