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Optical instruments
(b) A person needs a lens of power of focal length 0.5 cm be placed to
– 4.5 D for the correction of form an image at infinity? What is
his vision. the total angular magnification?
(i) What kind of defect in 6. In a particular compound microscope,
vision is he suffering? the objective lens and eyepiece lens
(ii) What is the focal length of are 15 cm apart. The focal length of
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the collective lens? the objective lens is 2.0 cm, while
(iii) What is the nature of the that of the eyepiece lens is 6.25 cm.
corrective lens? (a) How far from the objective lens
3. Read the passage carefully and should an object be placed in
answer the following questions given order to obtain the final image
below. of a distant vision?
The diameter of the eyeball is about (b) What is the total magnifying
2.3 cm, and a normal eye can adjust power of the microscope?
the focal length of its eye lens to see 7. Explain the meaning of the following
objects situated anywhere from terms as used in optical instruments.
25 cm to an infinite distance away (i) Magnifying power
from it. (j) Accommodation
(a) What is the power of the (normal) 8. Why are prism binoculars preferred
eye lens when the ciliary muscles over traditional ones?
are fully relaxed?
(b) What is the power of the (normal) 9. (a) Explain how the image of an
eye lens when the ciliary muscles object is formed in the human
are in their maximum contract eye.
position? (b) Give two defects of the human
(c) What is the maximum variation eye and explain how they can be
in the power of the lens when it corrected.
adjusts itself from the normal (c) Describe two ways in which a
relaxed position to the position lens camera and the human eye
where one can see the nearby are similar.
object clearly? (d) Describe two ways in which a
4. An astronomer wants to order a large lens camera and the human eye
concave mirror for a telescope that are different.
will produce high-quality images. 10. The objective and eyepiece of a
Explain and advise whether the compound microscope are 24 cm
astronomer should order a spherical apart. Suppose the focal lengths of
mirror or a parabolic mirror. the objective and the eyepiece are 3
5. An astronomical telescope is used to cm and 9 cm, respectively.
view an object at infinity and has an (i) Where must a specimen be
objective lens with a focal length of located to produce a final virtual
15.0 cm. Where must the eyepiece image at infinity?
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Physics Form 2 Final.indd 239 25/10/2025 10:28
