1. Using Lenses

2. Aims Be able to describe the behavior of light as it passes through a convex lens. Know how to measure the focal length of a convex lens.

3. glasses Lenses Because lenses refract light in a predictable way, they have been incorporated into everyday optical appliances such as... A lens can be made of glass or plastic. cameras binoculars

4. You also have a lens inside each eye – each lens is behind the pupil. Lenses Pupil

5. There are two main types of lens: Lenses - Types Concave lensesConvex lenses To help you remember the difference just think about a cave that goes into a hillside, i.e. concave lenses curve inwards.

6. This means that the light rays bend inwards and become closer together. Use the animation to see this happen. Convex Lenses The point at which the light rays converge (meet) is called the principal focus (F). The distance from the middle of the lens to the principal focus is the focal length ( f ). Convex lenses are also referred to as converging lenses. Convex lenses refract light rays causing them to converge.

7. Convex Lenses - Light Ray Diagrams The principal focus of a biconvex lens...

8. The focal length varies according to the thickness of the lens. A thick convex lens has a shorter focal length because it converges rays of light strongly. A thin convex lens has a long focal length because it converges the light rays more gently. Convex Lenses - Focal Length The distance from the centre of the lens to the principal focus is known as the focal length of the lens. Use the animation to find out how the thickness of the lens affects the focal length...

9. Finding the Focal length of convex lens

10. Convex lenses can be used to produce a variety of different types of images, for example: Images Produced by Convex Lenses  inverted  real  magnified or diminished Note: the image size depends upon the distance that the screen or viewer is behind the lens.

11. Magnified and Diminished Images

12. Magnification is given a numerical value. If the magnification is greater than 1.0 then the image produced by the lens is larger than the original object. For example x 2 means that the image is twice as big as the object is in real life. Original object Magnification x 2 Magnified and Diminished Images

13. For example, x ½ means that the image is half as big as the object is in real life. In this case the image is said to be diminished. If the magnification is less than 1.0 then the image produced by the lens is smaller than the original object. Original object Magnification x ½ Magnified and Diminished Images

14. Light Ray Diagrams Use the following animation to find out how to draw ray diagrams...

15. Convex Lenses - Light Ray Diagrams

16. Light Ray Diagrams Use the following animations to find out how the position of the object affects the image produced...

17. Converging Lens - Image Formation (1) When the object is between the lens and the principal focus (F')... The image is virtual, erect, behind the object and magnified.

18. Converging Lens - Image Formation (2) When the object is at the principal focus (F')... The image is only formed at infinity.

19. Converging Lens - Image Formation (3) When the object is between the principal focus (F') and 2x the focal distance (2F')... The image is beyond 2F, real, inverted and magnified.

20. Converging Lens - Image Formation (4) When the object is at 2x the focal length (2F')... The image is formed at 2F, and is real, inverted and the same size as the object.

21. Converging Lens - Image Formation (5) When the object is beyond 2x the the focal length (2F')... The image is formed between F and 2F, and is real, inverted and diminished.

22. Converging Lens - Image Formation (6) When the object is at infinity... The image is formed at F, and is real, inverted and diminished.