1. UNIT 8 Light and Optics

2. ConcepTest 35.2b Mirror II
1) same as your height
2) less than your full height but more than half your height
3) half your height
4) less than half your height
5) any size will do
You stand in front of a mirror. How tall does the mirror have to be so that you can see yourself entirely?

3. ConcepTest 35.2b Mirror II
1) same as your height
2) less than your full height but more than half your height
3) half your height
4) less than half your height
5) any size will do
You stand in front of a mirror. How tall does the mirror have to be so that you can see yourself entirely?
Trace the light rays from the image’s foot to the mirror and then to the eye. Since we know that qi = qr , you need a mirror only half your size.

4. ConcepTest 35.2c Mirror III
1) No.
2) Yes.
3) Depends on the mirror.
4) Depends on the person.
Does this depend on your distance from the mirror?

5. ConcepTest 35.2c Mirror III
1) No.
2) Yes.
3) Depends on the mirror.
4) Depends on the person.
Does this depend on your distance from the mirror?
The further you step back, the smaller the incident and reflected angles will be. But the rays will still be reflected at the same points, so the ray from the foot will still be reflected at mid-height.

6. Thursday February 16th
Light and Optics

7. TODAY’S AGENDA UPCOMING… Curved Mirrors Concave
Thursday, February 16
TODAY’S AGENDA
Curved Mirrors Concave
Hw: Practice B (all) p462
UPCOMING…
Fri: NO School
Mon: Curved Mirrors Convex
Tue: Problem Quiz #1
Color and Polarization
Wed: Refraction

8. Chapter 13
Light and Reflection

9. Formation of Images by Spherical Mirrors
Spherical mirrors are shaped like sections of a sphere, and may be reflective on either the inside (concave) or outside (convex).

10. Formation of Images by Spherical Mirrors
Rays coming from a faraway object are effectively parallel.

11. Formation of Images by Spherical Mirrors
Parallel rays striking a spherical mirror do not all converge at exactly the same place if the curvature of the mirror is large; this is called spherical aberration.

12. Formation of Images by Spherical Mirrors
If the curvature is small, the focus is much more precise; the focal point is where the rays converge.

13. Formation of Images by Spherical Mirrors
Using geometry, we find that the focal length is half the radius of curvature:
Spherical aberration can be avoided by using a parabolic reflector; these are more difficult and expensive to make, and so are used only when necessary, such as in research telescopes.

14. Formation of Images by Spherical Mirrors
We use ray diagrams to determine where an image will be. For mirrors, we use three key rays, all of which begin on the object:
A ray parallel to the principal axis; after reflection it passes through the focal point.
2. A ray through the focal point; after reflection it is parallel to the principal axis.
3. A ray through the focal point; after reflection it is parallel to the principal axis.

15. Images Formed by Spherical Mirrors
Concave Mirror C
center of
curvature = R R =
radius C
Principle Focal Point

16. Images Formed by Spherical Mirrors
Image Characteristics
Type:
Real or Virtual
Size:
Larger, Smaller, or Same (as the Object)
Orientation:
Upright or Inverted
do:
always positive
di:
real is positive; virtual is negative f:
In front of mirror is positive; Behind mirror is negative

17. Images Formed by Spherical Mirrors
Concave Mirror
Image Characteristics
Case #1
parallel ray
real
smaller
inverted
focal ray
central ray
image
image found between C and f

18. Images Formed by Spherical Mirrors
Concave Mirror
Image Characteristics
Case #2
real
same
inverted
image
image found at the C

19. Images Formed by Spherical Mirrors
Concave Mirror
Image Characteristics
Case #3
real
larger
inverted C
image
image found beyond C

20. Images Formed by Spherical Mirrors
Concave Mirror
Vampire case
Image Characteristics
Case #4
No image C

21. Images Formed by Spherical Mirrors
Make-up case
Concave Mirror
Case #5
image C
Image Characteristics
virtual
larger
upright
image found behind mirror

22. Images Formed by Spherical Mirrors
Concave Mirror
Light Source at
the Focal Point
Produces Parallel Rays of Light

23. Images Formed by Spherical Mirrors
Concave Mirror do di f ho hi
h i h o = d i −f f

24. Images Formed by Spherical Mirrors
Concave Mirror do di f ho hi

25. Images Formed by Spherical Mirrors
h i h o = d i d o
→ d o d i −f =f d i
d o d i − fd o =f d i →
d o d i =f d i + fd o

26. Images Formed by Spherical Mirrors
d o d i =f d i + d o →
d i d o d i + d o d o d i = 1 f

27. Images Formed by Spherical Mirrors
Concave Mirror
Virtual Image f

28. Images Formed by Spherical Mirrors
Concave Mirror do f ho hi di
h i h o = d i +f f

29. Images Formed by Spherical Mirrorsho hi do di
Concave Mirror
Magnification
M > 1 Larger
M < 1 Smaller
M Upright
M Inverted
M = 1 Same
M =

30. Images Formed by Spherical Mirrors
A object is placed between a concave mirror and its focal point. The image formed is
(A) virtual and inverted.
(B) virtual and upright.
(C) real and upright.
(D) real and inverted.

31. Images Formed by Spherical Mirrors (Problem)
A mirror at an amusement park shows an upright image of any person who stands 1.4 m in front of it. If the image is three times the person’s height, what is the radius of curvature?
M =
The image characteristics identify
the case as concave #5 (larger, virtual,
and upright).
3 = =
di = -4.2 m

32. Images Formed by Spherical Mirrors
If you stand in front of a concave mirror, exactly at its focal point,
(A) you will see your image at your same height.
(B) you won't see your image because there is none.
(B) you will see your image, and you will appear smaller.
(C) you will see your image and you will appear larger.

33. END