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# P8 converging lens

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IGCSE Physics Lens presentation

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### P8 converging lens

1. 1. Image formation by a converging lens
2. 2. Know the terms:Principal axis / optical centre / principal focus / focal length
3. 3. Refraction by lenses
4. 4. Drawing ray diagrams
5. 5. 3 Rules to follow:1.draw the ray parallel to the principal axis and it converges through the principal focus (F) on the other side2. draw the ray through the optical centre and it passes through in a straight line (not refracted)3. draw the ray through the principal focus on the object side of the lens and it is refracted parallel to the principal axis!
6. 6. Where is the image?
7. 7. Do you need convincing?
8. 8. Why does the ray from the bottom of the object appear on the principal axis? What can we say about the image: • Inverted or Upright position? • Reduced or Magnified?•Its location(related to 2F and which side it appears on)
9. 9. Where is the object? Where is the image?
10. 10. Can an image be bigger than the object?
11. 11. Magnifying glass
12. 12. Real or Virtual?Real images are produced when theobject is located a distance greater thanone focal length from the lens.A virtual image is formed if the object islocated less than one focal length fromthe converging lens. When refracted raysdiverge, a virtual image is formed becausethe rays cannot be focused onto a screen.
13. 13. Explaining the virtual image.When refracted rays diverge, a virtual image is formed.The image location can be found by tracing all light raysbackwards until they intersect. The refracted rays seemto be diverging from this point; thus, the point ofintersection of the extended refracted rays is the imagepoint. Since light does not actually pass through thispoint, the image is referred to as a virtual image.
14. 14. Wierd / Strange / X files?
15. 15. Object at F gives no image!The light rays neither converge nor divergeafter refracting through the lens.The refracted rays are traveling parallel to eachother.So, the light rays will not converge to form a realimage; nor can they be extended backwards onthe opposite side of the lens to intersect toform a virtual image.
16. 16. Remember: 3 Rules to follow!1.draw the ray parallel to the principal axis and it converges through the principal focus (F) on the other side2. draw the ray through the optical centre and it passes through in a straight line (not refracted)3. draw the ray through the principal focus on the object side of the lens and it is refracted parallel to the principal axis!
17. 17. Object location:Image location:Image size:Image position:
18. 18. Object location:Image location:Image size:Image position:
19. 19. Object location:Image location:Image size:Image position:
20. 20. Object location:Image location:Image size:Image position:
21. 21. Well done!