6.3 Image Formation By lenses

6.3 Image Formation :
Concave And Convex
Lenses

BY CIKGU SALMIAH SAMSUDIN
SMKA Tun Ahmad Zaidi

OBJECTIVES

Be By the end of this section, you will be able to:
List List the rules for ray tracking for thin lenses.
Illustrate Illustrate the formation of images using the technique of ray tracking.
Determine Determine power of a lens given the focal length.

LENSES

• Lenses are found in a huge array of
optical instruments, ranging from a
simple magnifying glass to the eye to a
camera’s zoom lens. In this section, we
will use the law of refraction to explore
the properties of lenses and how they
form images.

FOCAL POINT F
The point at which the light rays cross is
called the focal point F of the lens

FOCAL LENGTH f. CONVERGING OR CONVEX LENS
The distance from the center The lens in which light rays that enter it
of the lens to its focal point is parallel to its axis cross one another at a single
called focal length f. point on the opposite side with a converging
effect is called converging lens.

FOCAL POINT F DIVERGING LENS
The point at which the light rays cross is
called the focal point F of the lens • A lens that causes the light rays to
bend away from its axis is called a
diverging lens

Guidelines for rays falling on the concave and
convex lenses

1.When a ray strikes concave or convex lenses obliquely at its
pole, it continues to follow its path.

2.When a ray, parallel to the principal axis strikes concave or
convex lenses, the reflected ray passes through a focus on the
principal axis.

3.When a ray, passing through focus strikes concave or convex
lenses, the reflected ray will pass parallel to the principal axis.

CONVEX LENSES IMAGE
Diminished,
Inverted, Real
When an object is placed at infinity, the real (DIR)
and inverted image is formed at the focus
point. The size of the image is much smaller
(diminished) than that of the object

> 2 IMAGE
Diminished,
• When an object is placed behind the Inverted, Real
center of curvature, the real and inverted (DIR)
image is formed between the center of
curvature and focus. The size of the
image is smaller (diminished) as
compared to that of the object.

= 2 IMAGE
Same Size,
When an object is at the center of Inverted, Real
curvature, the real and inverted image (SIR)
is formed at the other center of
curvature. The size of the image is the
same size as the object.

•

2 < < IMAGE
Magnified,
• When an object is placed in between Inverted, Real
the center of curvature and focus, the (MIR)
real and inverted image is formed
behind the center of curvature. The
size of the image is larger (Magnified)
than that of the object

= IMAGE
Magnified,
Upright,
Virtual (MUV)

• When an object is placed at
the focus, a virtual and
upright image is formed at
infinity. The size of the
image is much larger than
that of the object

< IMAGE
Magnified,
• When an object is placed in Upright,
between focus and pole, a Virtual (MUV)
virtual and upright image is
formed. The size of the
image is larger (Magnified)
than that of the object.

Concave Lenses IMAGE
Diminished,
When an object is placed at a Upright,
finite distance from the lens, a Virtual (DUV)
virtual and upright image is
formed between the pole and
the focus of the convex lens.
The size of the image is smaller
(diminished) than that of the
object

Summary of Image Formation by Concave and Convex Lens

Image formation by Concave Lens

Object Location Image Location Image Nature Image Size
Highly Diminished
Infinity At F2 Virtual and Upright Diminished

Beyond Infinity and Zero Between F1 and Optical center Virtual and Upright

Image formation by Convex Lens

Object location Image location Image nature Image size
Real and Inverted Diminished
Infinity At f Real and Inverted Diminished
Real and Inverted Same Size
Beyond 2f Between 2f and f
Real and Inverted Magnified
At 2f At 2f
Magnified
Between 2f and f Beyond 2f
Magnified
At f At infinity Virtual and Upright

Between f and 0 On the same side as the object Virtual and Upright

Draw ray diagram of convex and concave lenses

https://drive.google.com/file/d/1WyaFVXP4V6NOuLKmFEvc https://youtu.be/S2Rn3H-_Vew
Qm6vHDBRpvg_/view?usp=sharing https://youtu.be/Tr_b9PTV-dI