A thin converging lens of focal length cm in air is held above a postage stamp so…
PHYSICS · Multi-part · Fermi University Physics · Optics & Photonics · Geometrical optics and imaging · Geometrical optics and imaging
Optics and Photonics, Ch Image formation by mirrors and lenses
Problem
A thin converging lens of focal length f=+12.0 cm in air is held above a postage stamp so that the stamp lies on the axis 8.0 cm from the lens. The stamp bears a printed mark 5.0 mm tall, standing above the axis. Rays are paraxial and the lens is thin. Sign convention CV1: so>0 for a real object on the left, si>0 for a real image on the right, heights positive above the axis.
((a)) On paper, draw the three principal rays from the top of the mark (the ray parallel to the axis, the ray through the lens centre, and the ray that arrives as if it came from the front focal point, found by drawing the line from that focal point through the top of the mark), extending the emergent rays backwards with broken lines where they do not meet in front of the lens. Then compute si from the thin lens equation.
((b)) Compute the transverse magnification MT and the image height, and say from the sign of si whether the image is real or virtual.