The Compound Microscope

Fig. 6.14. A compound microscope  

A compound microscope (Fig. 6.14) uses two converging lenses of short focal length. The first lens, the objective, has a very short focal length and a second lens, the eyepiece, has a focal length of a few centimeters. The two lenses are separated by a distance that is much greater than either these focal lengths. The objective lens produces a real image of a closer object. The eyepiece, which serves as a simple magnifier, produces a virtual, enlarged image. Combinations of eyepieces with different focal lengths and different objectives can produce a wide range of magnifications (from ‘Physics for scientists and Engineers’).

Exercise 78. Match each term (1−9) to its definition (a−i).

1. Microscope a) the lens or combination of lenses in an optical instrument nearest the eye of the observer

2. Shutter b) a mirror with a curved reflective surface, which may be either convex or concave

3. Refracting c) a device for recording visual images in the telescope form of photographs, movie film, or video signals

4. Reflecting d) an optical instrument used for viewing very telescope small objects

5. Eyepiece e) the lens or mirror in a microscope or other optical instrument that first receives light rays from the object and forms the image

6. Curved mirror f) a mechanical device on a camera that opens and closes to control the time of a photographic exposure

7. Aperture g) a telescope in which a mirror is used to collect and focus light

8. Objective h) a telescope that uses a converging lens to collect light

9. Camera i) an adjustable opening in an optical instrument (a camera or telescope), that limits the amount of light passing through a lens or onto a mirror

Exercise 79. Look for the words and word combinations in the text which have the opposite meanings to the words below.

blurred image ______________________

close object, nearby object ______________________

simple ______________________

to increase, enhance ______________________

virtual image ______________________

diverging lens ______________________

decrease, narrow, shorten ______________________

convex ______________________

Exercise 80. Answer the questions to the text.

1. What optical instruments do you know?

2. What are the main components of a photographic camera?

3. What image does the lens in a camera form?

4. What is the shutter?

5. What is exposure time?

6. What is an aperture used for?

7. What types of telescopes do you know?

8. What is the difference between a refracting telescope and a reflecting telescope? Which one is the more effective? Why?

9. What types of lenses does a compound microscope use?

10. What are the main components of a microscope?

Video watching ‘Amazing History of the Telescope’ (Video 6.3)

Exercise 81. A) Watch the video extract ‘Amazing History of the Telescope’ where Dr. J (astronomer Joe Liske) tells about the early history of the telescope and match the scientists with their activities and discoveries.

Name	Activity / Discovery /Invention
1. ___, ___, ___, ___ Galileo Galilei	a) was the first to invent the telescope but he didn’t use it to look at the stars and thought that his invention would mainly benefit seafarers and soldiers;
2. ___, ___ Hans Lippershey	b) discovered dark spots on the sun;
3. ___ Sacharias Jannsen	c) was Lippershey’s competitor and also claimed the invention of the telescope;
4. ___ Johannes Keppler	d) produced the first reliable maps of the moon showing what he believed to be continents and oceans;
5. ___ Michael van Langren	e) pointed his home-made telescope at the moon, the planets and the stars in 1609
6. ___ Johannes Hevelius	f) discovered Uranus in 1781;
7. ___, ___, ___ Christian Huygens	g) found that while viewing a distant object through combination of a convex and a concave lens, the object appeared closer and magnified;
8. ___,____, ___, ____ William Herschel	h) discovered the phases of Venus – from crescent to disc to crescent;
	i) discovered that the Milky Way must be a flat disc;
j) constructed probably the best telescope of his time;
k) in 1655 discovered Titan, the largest moon of Saturn;
l) cast the largest mirrors in the world in late 18^th century;
n) discovered that the moon is rough uneven and full of cavities;
o) built a huge telescope in his observatory at Danzig (Poland);
p) saw dark marking on bright polar caps on Mars;
q) built more than 400 telescopes during his life;
r) improved the design of the telescope in Prague;

B) Summarize all the information from the video in 15–20 sentences.

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