Question

An object is placed 20.0 cm from a converging lens having a focal length of magnitude 40.0 cm. a) Use graph paper to construct an accurate ray diagram for this situation. b) From your ray diagram, determine the location of the image. c) What is the magnification of the image? d) Check your answers to part b and c using the mirror equations.

Answer 1

given object distance
u = -20 cm
converging lens, focal length f = 40 cm

backtraced rays u -20 V-40 cm realrays from the object

a. the ray diagram is as under

b. location of image
   v = ?
   from lens formula
   1/v - 1/u = 1/f
   1/v + 1/20 = 1/40
   v = -40 cm

   from the graph, v is about - 40 cm to the left of the lens

c. magnification, m = v/u = -40/-20 = 2
   hence erect image of magnitude of magnification 2 is formed

d. this data can be verified from the graph