Page 221 - Physics_Form_2

Optical instruments
Task 6.2
1. Fill a transparent plastic bottle
with water and seal it.
2. Place the bottle filled with water
FOR ONLINE READING ONLY
on a page with text. Observe what
happens to the letters on the page.
Uses of a simple microscope
A simple microscope has a range of
applications. The following are some of
the uses of a simple microscope:
1. It is used to view specimens in a
laboratory.
2. It is used by watchmakers to view
small components of a watch.
3. It is used to read small prints.
4. It is used to concentrate light rays. lengths. This means that the object will
Exercise 6.1
1. A small object is placed 3 cm from
the lens of a simple microscope. The
focal length of the lens is 5 cm.
(a) Find the linear magnification
produced by the simple
microscope.
(b) How far from the lens should
you place the object to obtain
maximum magnification of the
image?
2. A magnifying glass of focal length
5 cm is used to magnify a small
object held 4 cm from the optical
centre of the lens. Determine the
position and magnification of the
formed image.
3. The magnifying power of a simple
microscope is 8. What will be the
focal length?
Physics Form 2 Final.indd 215
4. A student with a near-normal point
(25 cm) reads a story book with
small fonts using a thin convex lens
of focal length 5 cm.
(a) What are the closest and the
farthest distances the student
can read when viewing through
the magnifying glass?
(b) What are the maximum and
minimum angular magnification
(magnifying power) possible
using the above simple
microscope?
Compound microscope
The magnification of a simple microscope
9
is limited to M  for realistic focal
appear 9 times larger when viewed
using a simple microscope of maximum
magnification. For example, an object
whose size is 1 mm will be seen to be 9
mm when viewed through a magnifier.
However, the size of bacteria, for
example, is much smaller than 1 mm.
Thus, to see a bacterium, a magnification
larger than 9 is required. To achieve this,
a new microscope that uses two lenses in
such a way that one lens compounds the
effect of the other lens is normally used.
Such a microscope is called a compound
microscope.
Structure of a compound microscope
A compound microscope is composed
of a lens system, a lighting system and
a focusing system. The lens system is
made up of two convex lenses. A lens that
is placed nearer the object is called the
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