1. Lenses and Ray Diagrams
SNC2D

2. What is a lens?
A lens is a piece of transparent material that has been shaped in such a way that it refracts light rays to form an image.

3. Converging and Diverging
A converging lens (here, a double convex lens) focuses parallel rays to a single point and can form a ? image.

4. Converging and Diverging
A converging lens (here, a double convex lens) focuses parallel rays to a single point and can form a real image.

5. Converging and Diverging
A converging lens (here, a double convex lens) focuses parallel rays to a single point and can form a real image.
A diverging lens (here, a double concave lens) will always form a ? image.

6. Converging and Diverging
A converging lens (here, a double convex lens) focuses parallel rays to a single point and can form a real image.
A diverging lens (here, a double concave lens) will always form a virtual image.

7. The Anatomy of a Lens
Note that there are two foci, one on either side of the lens, and that rather than C (the centre of curvature), we have 2F (twice the focal length).

8. The Anatomy of a Lens
Note that there are two foci, one on either side of the lens, and that rather than C (the centre of curvature), we have 2F (twice the focal length).

9. Refraction Rules for a Converging Lens
An incident ray travelling parallel to the principal axis will refract such that it travels through the focal point on the far side of the lens.

10. Refraction Rules for a Converging Lens
Note that even though the refraction occurs at both interfaces, we draw it as if it were occurring at the vertical axis.
Reality:
How we draw it:

11. Refraction Rules for a Converging Lens
An incident ray travelling through the focal point will refract such that it travels parallel to the principal axis on the far side of the lens.

12. Point to Note
Not all converging lenses are double-convex lenses. Converging lenses may have different shapes.
When drawing ray diagrams, therefore, we ignore the shape of the lens and refract the rays at the line representing the vertical axis.

13. Refraction Rules for a Diverging Lens
An incident ray travelling parallel to the principal axis will refract such that its extension travels through the focal point on the near side of the lens.

14. Refraction Rules for a Diverging Lens
An incident ray travelling towards the focal point on the far side of the lens will refract such that it travels parallel to the principal axis on the far side of the lens.

15. The 3rd Rule (for both lenses)

16. Ray Diagrams Redux
We can use ray diagrams to locate and describe the characteristics of an image.

17. Ray Diagrams Redux
We can use ray diagrams to locate and describe the characteristics of an image.
Step 1: Draw the incident rays (parallel to the axis, through the focus, and/or through the centre):

18. Ray Diagrams Redux
We can use ray diagrams to locate and describe the characteristics of an image.
Step 2: Draw the refracted rays according to the refraction rules:

19. Ray Diagrams Redux
We can use ray diagrams to locate and describe the characteristics of an image.
Step 3: Locate the image:

20. Ray Diagrams Redux Note that the image of an object beyond 2F is: S:L: T:

21. Ray Diagrams Redux Note that the image of an object beyond 2F is:
S: Smaller A: L: T:

22. Ray Diagrams Redux Note that the image of an object beyond 2F is:
S: Smaller
A: Inverted L: T:

23. Ray Diagrams Redux Note that the image of an object beyond 2F is:
S: Smaller
A: Inverted
L: Between F and 2F T:

24. Ray Diagrams Redux Note that the image of an object beyond 2F is:
S: Smaller
A: Inverted
L: Between F and 2F
T: Real

25. Image Characteristics
If the object is at 2F, the image is:
S: the same size
A: inverted
L: at 2F
T: real

26. Image Characteristics
If the object is between 2F and F, the image is:
S: larger
A: inverted
L: beyond 2F
T: real

27. Image Characteristics
If the object is at F, an image is not formed.

28. Image Characteristics
If the object is between F and the lens, the image is:
S: larger
A: upright
L: further from the lens
T: virtual

29. Image Characteristics
For a diverging lens, the image is always:
(S) smaller, (A) upright, (L) closer to the lens, and (T) virtual.

30. More Practice
Draw scaled (i.e. measured with a ruler) ray diagrams to determine the answers to page 462 #6 and #10.