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23. Light: Geometric Optics
23.1 The Ray Model of Light
23.2 Reflection - Plane Mirror
23.3 Spherical Mirrors
23.5 Refraction - Snell’s law
23.7 Converging and Diverging Lenses
Concave Mirror Problem
A 3 cm high candle is located 5 cm from a concave mirror whose radius of curvature is 20 cm. What are the characteristics of the image?
Concave Mirror Problem
f = 10 cm
1/do + 1/ di = 1/f
1/5 + 1/ di = 1/10
1/ di = - 1/10
di = - 10 cm
The image is 10 cm behind the mirror, virtual, upright, and magnified 2X
m = - di / do
Concave Mirror Problem
Makeup mirror!
If the object is within the focus of the concave mirror the image is enlarged (magnified), upright
but virtual … it’s all in your head!!!
Convex Mirror Problem
A 3 cm high candle is located 5 cm from a convex mirror whose radius of curvature is 20 cm. What
are the characteristics of the image?
Convex Mirror Problem
f = - 10 cm
1/do + 1/ di = 1/f
1/5 + 1/ di = - 1/10
1/ di = - 3/10
di = - 3.3 cm
The image is 3.3 cm behind the mirror, virtual, upright, and reduced in size
m = - di / do
m = 1 / 3
Refraction Problem
The index of refraction of glass is 1.5. A ray of light is incident on a glass pane at an angle of 600. Calculate the angle of refraction.
Refraction Problem
n = sin i / sin r
1.5 = sin 600 / sin r
1.5 = 0.866 / sin r
sin r = 0.866 / 1.5
sin r = 0.58
r = 350
Lens Problem
A 35 mm slide projector uses a converging lens with f = 20 cm. The screen is 3 m away. How far is the slide from the lens?
Lens Problem
1/do + 1/ di = 1/f
1/do + 1/ 300 = 1/20
1/do = 1/20 - 1/ 300
do = 21. 4 cm
m = - di / do
m = - 300 / 21.4
m = -14
Image is real, inverted, magnified