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Physics for Secondary Schools
9. Attach your microscope to the stand 3. Suppose you have lenses A and B
and try to observe different small having focal lengths 100 cm and 4
objects using your own microscope. cm, respectively. If asked to choose
one as an eyepiece, which one would
Question you opt for, and why?
FOR ONLINE READING ONLY
What is the nature of images of 4. (a) Draw a labelled ray diagram of a
different objects when viewed through compound microscope. Explain
your microscope? briefly its working principle.
(b) In a compound microscope, why
should the objective lens form
The intermediate image formed by a an image at a point around the
compound microscope is real, inverted focal point of the eyepiece?
and magnified.
Exercise 6.2 Astronomical telescope
1. (a) Draw a labelled ray diagram The human eye has limitations when
showing the formation of a viewing objects that are very far from
final image by a compound the observer. When the object is at a
microscope at the least distance distance far from the point 2F of the eye
of distinct vision. lens, its image is formed at the focal point
(b) A compound microscope has an of the eye lens. However, this image is
extremely small and sometimes cannot
objective lens of focal length 2 be decoded by the brain. How can this
cm and eye piece of focal length limitation be overcome? Astronomers
6 cm. An object is placed 2.4 cm use a device named an astronomical
from the objective lens. If the telescope to observe the universe and
distance between the objective its components, which are extremely far
lens and eyepiece is 17 cm, find from our eyes.
the distance of the final image
from the eye piece.
2. The total magnification produced Structure of an astronomical telescope
by a compound microscope is 20. Just like the compound microscope, an
The magnification produced by astronomical telescope uses two convex
the eyepiece is 5. The microscope lenses: the objective lens and the eyepiece.
is focused on a certain object. The It also consists of a focusing system for
distance between the objective and adjusting the sharpness and clarity of the
eyepiece lens is 14 cm. If the least image. However, unlike the compound
distance of distinct vision is 20 cm, microscope, the objective lens of a
calculate the focal length of the telescope has a large focal length while the
objective and the eyepiece lens. eyepiece has a much shorter focal length.
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Student’s Book Form Two
Physics Form 2 Final.indd 220 25/10/2025 10:28
