Ilona and Olivia observe a virtual image formed by an object placed a distance f
ID: 1300607 • Letter: I
Question
Ilona and Olivia observe a virtual image formed by an object placed a distance f/2 in front of a
convex lens of focal length f. They argue about where to place a concave lens of focal length ?f
to have a virtual image at the same location relative to the lens that they had with the convex lens. Ilona says that the object should also be placed a distance f/2 in front of the concave lens. Olivia says that this won't work. Which one, if either, is correct, and why?
a. Ilona, because concave and convex lenses produce virtual images at equal image distances when the object distances are equal.
b. Ilona, because both p and q are negative for a concave lens.
c. Olivia, because both p and q are positive for a concave lens.
d.Olivia, because if q= -f/2 , then p was p = ?.
e.Olivia, because if q = ?f , then p was p = ?
Explanation / Answer
1/p + 1/ = 1/f
1/(f/2) + 1/q = 1/f
2/f + 1/q = 1/f
1/q = -1/f
q = -f
for concave lens
S' = -q
1/p - 1/f = -1/f
p = ?
e.Olivia, because if q = ?f , then p was p = ?