of sources, such as the sun, a light bulb, or a radio transmitter. It takes the form
of a wave similar in shape to an ocean wave.
Awave has two characteristics. These are the wave height and the wave-
length. The wave height is the highest level above the surface traveled by
the wave. Let’s say that you’re traveling across a calm stretch of ocean. This
is the surface. Your boat is then pushed high above the surface by a swell—the
wave height—before returning to the surface. The wavelengthis the distance
between the highest point of two waves. That is, the distance the boat trav-
els between the highest point of the first wave and the highest point of the
second wave.
Waves of electromagnetic radiation are in a continuous scale and are
clustered into groups called bands.They are given names based on their
wavelengths. Some are probably familiar to you, such as x-rays, visible light
waves, and radio waves. These groups are assembled into the electromagnetic
spectrum.
Waves such as light waves are generated from a source such as the sun and
strike an object such as your friend. Your friend absorbs some light waves and re-
flect other light waves. Your eyes detect only the reflected light waves.
It is this principle that enables you to observe a microorganism using a micro-
scope. Light waves from either a light bulb or room light are reflected on to the
microorganism. Reflected light waves are observed using the microscope. As
you’ll learn in Chapter 4, sometimes a microorganism reflects few light waves,
making it difficult to see under a microscope. Astainis used to cause the micro-
organism to reflect different light waves. Microorganisms are visible under an
electron microscope by directing waves of electrons onto the microorganism.
Some electron waves are absorbed and others are reflected. The reflected waves
are detected by an electronic circuit that displays an image of the microorganism
on a video screen.What Big Eyes You Have: Magnification
Light reflected from a specimen travels in a straight line to your eyes, which
lets you see the specimen at its natural size. You can magnify the size of the
specimen bylooking at the specimen through a concave lens. Aconvex lens(Fig.
3-2) is usuallymade out of glass or plastic; the back of the lens is bent inward
and the front is bent outward. It is like looking into a bubble. A magnifying
glass is a convex lens.(^52) CHAPTER 3 Observing Microorganisms