how are images formed with a convex lens

1. Presentation
Lenses
Magnification and focal length
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Mr. PG

2. • To find out how images are formed with
convex lenses, we have to consider certain
rules as regards to rays of lights coming from
different directions on the surface of the
lenses and how they get refracted.
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3. • First rule: A ray of light parallel to the
principal axis XY, on refraction passes through
the focal point F. This is shown in the figure
given below.
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4. • Second rule: A ray of light passing through
the optical centre O of a convex lens, goes
un-deviated along the same path.
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5. • Third rule: The third rule is inverse of the first
rule. When a ray of light passes through the
focus F and strikes a convex lens, the
refracted ray is parallel to the principal axis
XY.
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6. • From the above three rules, we can now study
how images are formed with the help of
convex lenses. The type of images formed
depends on where the object is positioned in
front of the lens. We will study a few typical
cases.
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8. • Case 1: object is placed between the optical
centre O and the focus F1
• Case 2: object is placed at focus F1
• Case 3: object is placed between the focus F1 and
2 F1
• Case 4: object is placed at 2 F1
• Case 5: object is placed at a distance beyond 2 F1
• Case 6: object is placed at a far off distance
beyond 2 F1 (or at infinite distance).
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9. Case one
• The image is behind the lens and hence is
virtual
• The image is erect and not inverted
• The image is magnified
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10. Case 2
• The image is formed at infinity
• The image is inverted and real
• The image is highly magnified
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11. Case 3
• The image is formed beyond 2 F1
• The image is inverted and real
• The image is magnified.
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12. Case 4
• The image is formed at 2 F2 on the other side
of the lens
• The image is inverted and real
• The image is same size as that of the object.
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13. Case 5
• The image is formed between F2 and 2 F2
• The image is inverted and real
• The image is reduced in size.
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14. Case 6
• The image is formed at F2
• The image is inverted and real
• The image is highly reduced in size
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