Download Lenses

Lenses
Refraction
• Light moves through different substances at different speeds
EX light moves more slowly through water than air
• When light passes from one material into another, it changes speed
and bends
• Refraction is the bending of light
Refraction Video
Refraction Video
Types of Lenses
Two Types:
1. Converging
2. Diverging
Converging Lenses
• A converging lens causes light rays that are
parallel to the principal axis to converge(meet)
at one point (i.e., the principal focus, F)
lens
Incident rays
F
Refracted rays
• Optical Centre (O)
centre of the lens
• Principal Axis
line through the
centre
–
–
optical
• Principal Focus (F) – point on principal
axis where light rays that are parallel to
principal axis converge after refraction
• Secondary Principal Focus (F’) – different
• F is on same side of lens as incident rays
• F’ is on opposite side as incident rays
Converging Lens – Labeling the Parts
Diverging Lenses
• A diverging lens causes parallel light rays to
diverge (spread apart).
lens
Incident rays
Refracted rays
•
•
•
•
same as Converging Lens:
Optical Centre (O)
Principal Axis
Principal Focus (F)
• Secondary Principal Focus (F’) – different
• F is on same side of lens as incident rays
• F’ is on opposite side as incident rays
Diverging Lenses – Labeling the Parts
The Rules for Locating Images in
Lenses
1. A ray parallel to the principal axis is refracted
through the principal focus (F).
2. A ray through the secondary principal focus
(F’) is refracted parallel to the principal axis.
3. A ray through the optical centre (O) continues
straight through without being refracted.
NOTE: Any two rules can be used to determine the
characteristics of an image through a lens.
Showing the Rules for Converging
Lenses
Showing the Rules for Diverging Lenses
Drawing Diverging Lens Diagrams
1. Draw a ray from the tip of the object parallel to
the principal axis. When it reaches the centre
of the lens, it appears to refract through the
principal focus.
2. Draw a 2nd ray from the tip of the object
through the optical centre (not refracted).
3. The VIRTUAL image appears where the rays
cross.