Page 243 - Physics_Form_2
P. 243
Optical instruments
Exercise 6.5 (a) Draw the ray diagram to
1. The distance from the cornea to the illustrate how the image of the
retina of someone’s eye is 2.1 cm. blackboard writing is formed by
Determine the effective focal length his eye lens when he is seated
of this eye if an object is, at the:
FOR ONLINE READING ONLY
(a) At infinity. (i) last desk
(b) Located 1 m away. (ii) front desk
(c) Located 25 cm away. (b) Name the defect of vision the
2. A far-sighted eye can only focus on student is suffering from. Also,
objects beyond 100 cm. What focal list two causes of this defect.
length and power of the contact lens (c) Name the kind of lens that
are needed to correct this problem? would enable him to see clearly
3. A near-sighted eye can only focus on when he is seated at the last
objects closer than 50.0 cm. What desk. Draw the ray diagram to
sort of contact lens will correct this illustrate how this lens helps
problem? Determine its power. him to see clearly.
4. (a) Differentiate between
magnifying power and Chapter summary
magnification of a lens.
(b) A near point of a long-sighted 1. Optical instruments use refraction or
patient is 90 cm. Determine: reflection of light to form different
(i) the focal length of a lens types of images.
that can be used to enable 2. Microscopes make it possible to see
the patient to see an object very small objects by producing an
which is at a distance of enlarged image of an object.
25 cm from the patient’s
eye 3. Telescopes and binoculars allow us
(ii) the power of the patient’s to see objects that are far away.
eye 4. Cameras provide us with a recorded
(iii) the magnification of the image of an object. The image can
patient’s eye lens be a still image or a moving image
5. A student finds the writing on the (video).
blackboard to be blurred and unclear 5. The human eye can discern colour,
when seated at the back desk of judge distance and see great detail
the classroom. However, he sees from both near and far positions by
clearly when sitting at the front desk, adjusting the focal length of its lens.
approximately 2 metres from the 6. Myopia is a condition in which close
blackboard. objects appear clearly, but far ones
237
Physics Form 2 Final.indd 237 25/10/2025 10:28
