Problem 3

A thin converging lens has focal length

f=20\,\mathrm{cm}

. An object of height

h_o=2.0\,\mathrm{cm}

is perpendicular to the axis,

u=30\,\mathrm{cm}

from the lens on the object side. Neglect thickness; use positive object distance and focal length,

v>0

for a real image beyond the lens, and

m=-v/u

. (a) Find image distance and nature. (b) Find magnification, image height, and orientation. (c) Locate a screen for a sharp image.

problems.proof.stepOf

1/v=1/20-1/30=1/60 cm^{-1}; v=60 cm

problems.proof.analysis

Solving gives $v=60\,\mathrm{cm}$ . Its positive sign confirms a real image beyond the lens.