1. 9.5 Light and Vision Pages 441-444

2. The Hypotheses Democritus Matter composed of atoms which are carried to the soul to be viewed Empedocles Matter composed of 4 elements Earth, Air, Wind and Fire and vision must be related to fire Light radiated from eye Galen Optic nerve conducted visual spirits

3. Today we accept the following theories: Sir Isaac Newton and Christian Huygens Particles of light (photons) travel in waves of various lengths Light enters the eye as it is reflected or transmitted from objects

4. Afterimages Two types of afterimages: Positive Afterimage Occurs after you look into a bright light and then close your eyes The image of the light can still be seen even with eyes closed Negative Afterimage Eye is exposed to bright coloured light for an extended period of time

9. Focusing the Image Refraction: slowing of light by dense material (cornea) Light is first bent by the cornea toward the pupil It is further bent by the lens to a focal point behind the lens Image is projected on the retina

10. Focusing the Image Light bent by cornea toward pupil Bent by lens to focal point Image projected on retina

11. Accommodation The adjustment of the lens to objects far and near Objects up close  pupil constricts in attempt to bring the image into focus Objects far away  pupil dilates to in an attempt to capture light

12. Vision Defects Glaucoma Build-up of aqueous humour Ducts are blocked Increases fluid pressure Lack of oxygen and neurons can result in blindness

13. Cataract Lens becomes opaque Prevents light from passing through Solution: remove lens and use strong eyeglasses or replace with plastic lens

14. Myopia (nearsightedness) Eye ball is too long Distant image is brought into focus in front of the retina Hyperopia (farsightedness) Eye ball is too short Distant image is brought into focus behind retina