Download Biology Specimen Room Tour - Shatin Tsung Tsin Secondary School

Shatin Tsung Tsin Secondary School
Biology Specimen Room Tour
Light Microscope & Electron microscope
Introduction
There are two main types of microscopes: light microscope and electron microscope. Light
microscope uses light as the illuminating source while electron microscope uses electron beam.
Compound light microscope
Electron microscope (www.skcc.org)
The best light microscope produces an effective magnification of 1,500. The resolution 1 (解像度)
is about 0.5μm. Further magnification is limited by the long wavelength of the visible light.
Electron microscope can produce a much higher magnification close to 1,000,000 because of the
short wavelength of electron beam. The resolution is in the region of nm. We cannot see the
image directly. To view the image, we have to develop a film.
Instructions
Go through the wall charts hung near the bench in the Specimen Room. You can observe the photos
taken by the electron microscopes.
Note
1. Resolution is the shortest distance that can be discerned by an optical system. It is governed
by the following formula: Kλ/nsinθ, where K = constant, λ=wavelength of illuminating
source, n = refractive index,θ= half angle
2.
Units: 1μm = 10-6m;
1nm = 10-9m
Questions
1. Explain why we cannot see the image formed by electron microscope directly?
2. Unaided eye has a resolution of 0.5mm. Do you think we can observe bacteria (size = 1μm)
3.
and viruses (size = 10-300nm) with (a) unaided eye; (b) light microscope; (c) electron
microscope
What does the development of microscopes facilitate the advancement of science?