Use principles of reflection and refraction to describe how lenses and mirrors work. **More good stuff available at: www.wsautter.com and http://www.youtube.com/results?search_query=wnsautter&aq=f

1. W. Sautter 2015

2. Normal
Line
Normal
Line
i
r
i
r
Glass
n = 1.5
Air
n =1.0
r = angle of refraction
i = angle of incidence
Light travels more slowly
in glass than air and
bends towards the normal
when entering glass from air
Light moving from
glass to air
increases speed
and bends away
from the normal
2

3. Virtual focus
Focus = -
Can form only virtual,
Erect and reduced
images
3

4. Principle
focus
Parallel rays
Focus = +
Can form real images
(enlarged or reduced
& inverted) or
Enlarged virtual images
4

5. Normal
Line
ri
Incident
ray
Reflected
ray
Mirror surface
Angles are ALWAYS measured from the NORMAL LINE 5

6. Parallel rays
Reflected rays
Real
Focus
Focal length = +
Forms real, inverted,
Reduced or enlarged
Image. Also forms
Virtual, erect,
Enlarged images.
6

7. Parallel rays
Reflected rays
Virtual focus
Focal length = -
Forms only virtual,
erect, reduced
images between
the virtual focus
and the mirror.7

8. Waves from a
Distant source
= crest
= trough
Barrier with
Two slits
In phase waves
Emerge from slits
Constructive
interference
Destructive
interference
8

9. Wavelength

Frequency

Velocity Wavelength

Frequency

Velocity
vx = 9

10. VISIBLE AND INVISIBLE LIGHT
• MOST “LIGHT” IS NOT VISIBLE TO THE HUMAN EYE !
• ONLY ABOUT 7 % OF THE KNOWN KINDS OF LIGHT
CAN BE SEEN WITHOUT SPECIAL INSTRUMENTATION.
10

11. POTASSIUM METAL
BATTERY
VOLTMETER
PHOTONS
PICKUP
WIRE
ELECTRONS
ONLY CERTAIN MINIMUM FREQUENCIES OF LIGHT
FREE THE ELECTRONS FROM THE METAL
(ONLY PHOTONS WITH ENOUGH ENERGY)
THE PHOTOELECTRIC EFFECT EXPERIMENT
11

12. Parallel ray
focus (f)2 f
vertex
Reflects thru
The focus
Reflects parallel
To principal axis
Principal axis
Reflects Back
Into itself
12

13. Parallel ray
f2 f
Image is:
Real
Inverted
Reduced
Appears between f & 2f
Object beyond 2f
13

14. Image is:
Real
Inverted
Same size
Appears at 2f
Parallel ray
f2 f
Object at 2f
14

15. Image is:
Real
Inverted
Enlarged
Appears beyond 2f
Parallel ray
2 f f
Object between
f and 2f
15

16. Image is:
Virtual
Erect
Enlarged
Appears behind the
mirror
Parallel ray
2 f f
ray thru 2f
Apparent
Convergence
Of rays
Object inside
focus
16

17. Angle of incidence = Angle of Reflection
For each ray
Dotted lines
Shows the
Apparent
Ray source
17

18. Parallel rays
Reflected rays
Virtual focus
Focal length = -
Forms only virtual,
erect, reduced
images between
the virtual focus
and the mirror.
Dotted lines
Shows the
Apparent
Ray focus
18

19. 19
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