This document discusses the uses and properties of lenses. It defines reflection and refraction, and describes how curved mirrors and different types of lenses work by bending light. Convex lenses converge light to a focal point, while concave lenses diverge light. Lenses are used in cameras, telescopes, and eyeglasses to focus light and form images. Cameras use lenses to admit more light and produce brighter, clearer pictures than a pinhole camera. The eye uses curved lenses to focus light onto the retina, and nearsightedness and farsightedness occur when the lens is too long or short. Telescopes also employ lenses and curved mirrors to magnify distant objects.

1. Uses of Lenses
October 30, 2014

2. Objectives
1. Diagram and define reflection and virtual image
2. Give examples of refraction and describe how it works
3. Diagram and describe the different types/uses of lenses

3. Law of Reflection
• The angle of reflection equals the angle of incidence
• Angle of Incidence – angle of strike (i)
• Angle of Reflection –angle of rebounds (r)
• Normal – imaginary line that extends perpendicular to the flat surface

4. Virtual Images
• Reflected image that we see in a mirror
• our minds perceive it not as a reflection, but as coming
out from the mirror

5. Look at a mirror it, appears that you are behind that mirror in
exactly the same position

6. Curved mirrors
• Convex mirror – curves outward, virtual image is smaller and
closer
• Concave mirror – curves inward, virtual image is larger and
further away

7. • What evidence can you use to support the claim that the
frequency of light does not change upon reflection?
• If you took a picture of your image while standing 2 m in
front of a plane mirror, what distance should you set your
camera to provide the sharpest focus?

8. Refraction
• The bending of light due to changing speed, passing from
one medium to another

9. • When light slows down (goes from gas to liquid) it refracts
toward the normal
• When light speeds up (solid to air) it refracts away from the
normal

10. • Why is it more dangerous to drive a car of a rainy day?
• If the speed of light were the same in all media, would
refraction still occur when light passes from one medium
to another?

11. Types of Lenses
• concave lens – where light that passes through diverges as if
it came from a point

12. • Convex lens – where light that passes through converges to a
single point

14. What are Lenses Used for?
1. Camera’s
2. Telescopes
3. Eyeglasses/Contacts

15. Camera’s
• Pinhole Camera:
• Simplest of camera’s
• A box with a pinhole in the front and film paper attached to the back
• Hole prevents overlapping rays and prints a very dim upside down
image

16. • Improved lens Camera
• Lens admits more light (takes less time)
• Allows more rays without overlapping (brighter more focused
image)

17. Explain in your own words how this
works.

18. The Eye
• How do the lenses in your eyes help you see?

19. Eyesight
• Nearsighted – can’t see far away
• Farsighted – can’t see close up
• What is the importance of the rays meeting at the retina?

20. NearsightedVision
• The lens becomes shorter and fatter
• Where do the rays come into focus?
• How can this be corrected?

21. FarsightedVision
• The lens becomes longer and skinnier
• Where do the rays come into focus?
• How can this be corrected?

22. How are camera’s and our eyes similar

23. Telescopes
• Galileo
• Kepler

24. Galileo’sTelescope

25. Kepler’sTelescope
• Using a second concave lens magnified the image even
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