1. College Physics, 7th Edition
Lecture Outline
Chapter 23
College Physics, 7th Edition
Wilson / Buffa / Lou
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2. 23.1 Plane Mirrors
Mirrors are typically coated with a compound of Sn, Al, or Ag because light isn’t transmitted through these elements.
The geometry of the mirror affects the size, orientation, and type of image.

3. 23.1 Plane Mirrors
The image formed by a plane mirror is upright, identical in size to the object, and as far behind the mirror as the object is in front of it.
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4. 23.1 Plane Mirrors Let’s remember…what is: do? di?
Virtual vs. real images?
Law of Reflection?
We can see all these things on the previous
slide.
Typically scientists are interested in 2 image features: height and orientation.

5. 23.1 Plane Mirrors The magnification is given by:
For a plane mirror, M = +1.
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6. 23.1 Plane Mirrors For a plane mirror, the image is ALWAYS Upright
Virtual
Unmagnified

7. 23.2 Spherical Mirrors
A spherical mirror is a section of a sphere. It may be concave or convex.
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8. 23.2 Spherical Mirrors
A concave mirror (left) focuses incoming parallel rays at the focal point. A convex mirror bends incoming parallel rays outward, as though they came from a focal point behind the mirror.
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9. 23.2 Spherical Mirrors
Thus, concave mirrors act as converging mirrors. (Bring light together)
Convex mirrors act as diverging mirrors (light rays move apart)
Focal Length – Distance from the vertex to focal point (f).
f = R/2
(For mirrors, it’s always half the radius of curvature)

10. 23.2 Spherical Mirrors
Images made by mirrors can be found by ray diagramming. There are 3 key rays to draw!
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11. 23.2 Spherical Mirrors
For a concave mirror, the type of image formed depends on the position of the object.
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12. 23.2 Spherical Mirrors
If the object is at the focal point, there is no image.
The focal point is a crossover point between real and virtual images.
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13. 23.2 Spherical Mirrors
An object is placed 39 cm in front of a converging spherical mirror of radius 24 cm.
A) Use a ray diagram to locate the image formed by this mirror.
B) Discuss the characteristics of the image.

14. 23.2 Spherical Mirrors
The spherical-mirror equation is valid for any object position:
Sign conventions for spherical mirrors are given on the next slide.
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15. 23.2 Spherical Mirrors
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16. 23.2 Spherical Mirrors
Another way we can calculate the magnification is given by:
What was the first way again??
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17. 23.2 Spherical Mirrors
A converging mirror has a radius of curvature of 30 cm. If an object is placed
a) 45 cm
b) 20 cm
c) 10 cm
from the mirror, where is the imaged formed, and what are its characteristics?

18. 23.2 Spherical Mirrors
A candle is 20 cm in front of a diverging mirror that has a focal length of -15 cm.
a) Use a ray diagram to determine whether the image formed is
Real, upright, magnified
Virtual, upright, magnified
Real, upright, reduced
Virtual, upright, reduced
Real, inverted, magnified
Virtual, inverted, reduced
b) Find the location and characteristics of the image

19. 23.2 Spherical Mirrors
For a convex mirror the process is similar, but the image will always be virtual.
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20. 23.3 Lenses
A converging lens brings incoming rays together at the focal point. These are convex lenses. [Light rays converge at focal point] Thicker at center
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21. 23.3 Lenses
The rays emerging from a diverging lens appear to have come from a single focal point. This is a concave lens. [Thinner at center]
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22. 23.3 Lenses
Both converging and diverging lenses come in a variety of shapes.
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23. 23.3 Lenses We like to assume the lens are thin.
If they are not, none of our things work…we have to do different math that you won’t be tested on.
There’s only one big difference between mirrors and lenses and that is the focal length for lenses does not equal R/2.

24. 23.3 Lenses
Images formed by lenses can be found just as mirror images were found. The first two rays:
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25. 23.3 Lenses Locating and confirming the image:
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26. 23.3 Lenses
An object is placed 30 cm in front of a thin converging lens of focal length 20 cm.
Use a ray diagram to locate the image.
Discuss the characteristics of the image.

27. 23.3 Lenses
The type of image formed by a converging lens depends on the position of the object. For a distant object:
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28. 23.3 Lenses

29. 23.3 Lenses
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30. 23.3 Lenses The thin-lens equation: Magnification:
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31. 23.3 Lenses
A converging lens has a focal length of 12 cm. For an object a) 60 cm, b) 15 cm, and c) 8.0 cm from the lens, where is the image formed, and what are the characteristics?

32. 23.3 Lenses
A converging lens forms an image on a screen. Then the lower half of the lens is blocked as shown in b. As a result, what happens? Only the top half of the image will show; only the bottom half; or the entire image will still be seen?

33. 23.3 Lenses
An object is 24 cm in front of a diverging lens that has a focal length of -15 cm.
a) Use a ray diagram to determine the characteristics of the image as well as the location.

34. 23.3 Lenses A diverging lens always forms a virtual image.
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