CHAPTER 13. GEOMETRICAL OPTICS 13.2
SOLUTION
Step 1 : Draw the picture to setup the problem
Draw the lens, principalaxis, focal points and the object.
F 1 Object
F 2
O
Step 2 : Draw the three rays tolocate image
- R 1 goes from the top of the object parallel to theprincipal axis, throughthe lens and
through the focal point F 2 on the other side of thelens.
- R 2 is the light ray which should go through the focal point F 1 but the object is placed
after the focal point! This isnot a problem, just trace the line from the focal point F 1 ,
through the top of the object, to the lens. Thisray then leaves the lensparallel to the
principal axis.
- R 3 goes from the top of the object through the optical centre with its direction un-
changed.
- Do not write R 1 , R 2 and R 3 on your diagram, otherwise it becomes too cluttered.
- Since the rays do not intersect on the right side of the lens, we need to trace them back-
wards to find the placewhere they do come together (these are the light gray lines).
Again, this is the position of the image.
F 1 Object
F 2
O
R 1
R 3
R 2
