13.5 CHAPTER 13. GEOMETRICAL OPTICS
- An object is at right angles to the principal axis of a convex lens. Theobject is 2 cm
high and is 5 cm from the centre of the lens, which has a focal length of10 cm.
Find the distance of theimage from the centre of the lens, and its height. Is it real or
virtual?
- A convex lens of focal length 15 cm producesa real image of height 4cm at 45 cm
from the centre of the lens. Find the distance ofthe object from the lensand its
height.
- An object is 20 cm from a concave lens. Thevirtual image formed isthree times
smaller than the object.Find the focal length ofthe lens.
- A convex lens produces a virtual image which is four times larger than the object.
The image is 15 cm fromthe lens. What is the focal length of the lens?
- A convex lens is usedto project an image of alight source onto a screen. The screen
is 30 cm from the light source, and the image istwice the size of the object. What
focal length is required,and how far from the source must it be placed?
- An object 6 cm high is place 20 cm from aconverging lens of focallength 8 cm.
Find by scale drawing the position, size and nature of the image produced.
(Advanced: check youranswer by calculation).
- An object is placedin front of a converginglens of focal length 12 cm. By scale
diagram, find the nature, position and magnification of the image whenthe object
distance is
(a) 16 cm
(b) 8 cm
- A concave lens produces an image three times smaller than the object. If the object
is 18 cm away from thelens, determine the focal length of the lens by means of a
scale diagram. (Advanced: check your answer bycalculation).
- You have seen howthe human eye works, how telescopes work andhow
microscopes work. Using what you have learnt,describe how you thinka camera
works.
- Describe 3 common defects of vision and discuss the various methods that are used
to correct them.
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