1. Light
By Neil Bronks

2. Laws of Reflection
The angle of incidence ,i, is always equal to the angle of reflection, r.
The incident ray, reflected ray and the normal all lie on the same plane.

3. Virtual Image An image that is formed by the eye
Can not appear on a screen d d

4. Real Image
Rays really meet
Can be formed on a screen F 2F

5. Ray Diagrams- Object outside 2F
1/. Inverted
2/. Smaller
3/. Real 2F F
The images can be formed on a screen so they are real.

6. Object at F F 2F
The image is at infinity

7. Object inside F 1/. Upright 2/. Magnified 3/. Virtual F
The image is behind the mirror

8. Convex Mirror 1/. Upright 2/. Smaller 3/. Virtual
The image is behind the mirror
1/. Upright
2/. Smaller
3/. Virtual F

9. Uses of curved mirrors Concave Mirrors Convex Mirror Security Mirrors
Dentists Mirrors
Make –up mirrors
Convex Mirror
Security Mirrors
Rear view mirrors

10. Example
An object is placed 20cm from a concave mirror of focal length 30cm find the position of the image formed. What is the nature of the image?
Collect info f=30 and u=20
Using the formula
V=60cm Virtual

11. Magnification What is the magnification in the last question?
Well u=20 and v=60 As 20
m=3
Image is magnified 6 2

12. Example
An object is placed 30cm from a convex mirror of focal length 20cm find the position of the image formed. What is the nature of the image?
Collect info f=-20 and u=30
The minus is
Because the
Mirror is
convex
Using the formula
V=60/5cm =12cm Virtual

13. MEASUREMENT OF THE FOCAL LENGTH OF A CONCAVE MIRROR
Crosswire u
Lamp-box
Screen v

14. Laws of REFRACTION
The incident ray, refracted ray and normal all lie on the same plane
SNELLS LAW the ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant for 2 given media.
sin i =constant =n (Refractive Index)
sin r

15. Proving Snell’s Law Sin i i r Sin r
Laser
Sin i i
Protractor
Glass Block r
Sin r
A straight line though the origin proves Snell’s law.
The slope is the refractive index.

16. Refractive Index
Ratio of speeds

17. Real and Apparent Depth
A pool appears shallower

18. REFRACTIVE INDEX OF A LIQUID
MEASUREMENT OF THE
REFRACTIVE INDEX OF A LIQUID
Cork
Pin
Apparent depth
Mirror
Real depth
Water
Image
Pin

19. Finding the Critical Angle…
1) Ray gets refracted
2) Ray still gets refracted
4) Ray gets internally reflected
3) Ray still gets refracted (just!)
THE CRITICAL ANGLE

20. Critical Angle
Varies according to refractive index

21. Practical Fibre Optics
It is important to coat the strand in a material of low n.
This increases Total Internal Reflection
The light can not leak into the next strand.

22. Lenses
Two types of lenses
Focal Point
Converging Lens Diverging Lens

23. Converging Lens- Object outside 2F
Image is
1/. Real
2/. Inverted
3/. Smaller 2F F

24. Object inside F
Image is
1/. Virtual
2/. Erect
3/. Magnified F

25. Magnification What is the magnification in the last question?
Well u=30 and v=12 As 12 30 2 5
Image is smaller

26. MEASUREMENT OF THE FOCAL LENGTH
OF A CONVERGING LENS
Lamp-box with crosswire
Screen
Lens v u

27. Diverging Lens
Image is
1/. Virtual
2/. Upright
3/. Smaller F F

28. Example
An object is placed 30cm from a diverging lens of focal length 20cm find the position of the image formed. What is the nature of the image?
Collect info f=-20 and u=30
The minus is
Because the
Diverging lens
Using the formula
V=60/5cm =12cm Virtual

29. Magnification What is the magnification in the last question?
Well u=30 and v=20 As 20 30 2 3
Image is smaller

30. Sign Convention f Positive V either f negative V f negative V f

31. Myopia (Short Sighted)
Image is formed in front of the retina.
Correct with diverging lens.

32. Hyperopia (Long-Sighted)
Image is formed behind the retina.
Correct with a converging lens

33. Power of Lens Opticians use power to describe lenses. P=
So a focal length of 10cm= 0.1m is written as P=10m-1
A diverging lens with a negative focal length f=-40cm=-0.4m
Has a power of P = -2.5m-1

34. The power of the total lens is
Lens in Contact
Most camera lens are made up of two lens joined to prevent dispersion of the light.
The power of the total lens is
Ptotal=P1+ P2