IIT JEE Physics (1978-2018: 41 Years) Topic-wise Complete Solutions

Paper Microscope

Objective

Make a microscope from a sheet of paper.

Introduction

The apparent size of an object (as seen by the eye) increases as the object comes closer to the eye. But you cannot bring the object too close to the eye as the image does not form on the retina. This is because the eye cannot decrease the focal length of the eye lens beyond a limit. With a pin hole in a paper you can overcome this difficulty.

A sheet of paper

Procedure

1. Take the sheet of paper ($$\approx 3'' \times 3''$$) and punch a small hole using the tip of your pen.
2. Make the hole smooth if there are threads coming out at periphery. This is your paper microscope.
3. Now take a printed page very close to your eye, say at 3-4 cm. You are not able to read what is written on the page.
4. Keeping the printed page in the same position, bring the paper microscope in between the eye and the page. Are you able to see the letters clearly?
5. The magnifying power of a simple microscope is defined as $$m=h_2/h_1$$ where $$h_2$$ is the size of the image on the retina when the microscope is used and $$h_1$$ is the size when the microscope is not used and the object is placed at the minimum distance of clear vision. Find the approximate magnifying power of the paper microscope.