1 .7 LIGHT and SIGHT

1. 1.7 LIGHT and SIGHT Learning outcome 1. Properties of light.2. Defects of vision3. Limitation of sights & ways to overcome4. Types of vision

2. Properties of Light Light travels in straight lines. What can you infer from the picture above?

3. Properties of Light What is the relation between “shadow formation” and “eclipse incidents” with this property of light? Light travels in straight lines.

4. Shadow Formation When light travels through opaque objects (does not allow light to pass through), shadow is formed. No shadow is formed when light travels through translucent/transparent object. Light travels in straight lines.

5. Phenomena of Eclipse • Occurs when the Moon passes between the Sun and the Earth, and the Moon fully or partially covers the Sun as viewed from a location on Earth Light travels in straight lines.

6. Properties of Light 1. Light is a form of energy.2. Light travels at a speed of 300 000 000 m/s.3. Light can be reflected and refracted.4. In nature, ordinary light is called white light which can be splitted into 7 colors (spectrum). 5. Light can be reflected and refracted.

7. REFLECTION OF LIGHT Reflection of light is the change in direction of a light ray when it hits a surface of an opaque object and bounces off the object. There are 2 types of reflection :- • Specular Reflection • Diffused Reflection

8. Specular & Diffused Reflection Parallel beam of light remain parallel after reflection from an even surface Rays are reflected in different directions from the uneven surface

9. REFLECTION OF LIGHT MIRRORS are good reflectors of light due to its smooth flat surface. The image formed is :- Virtual, Upright, Laterally Inverted (Your right hand is the image ‘s left hand in the mirror), Same size and the Same Distance behind the mirror as the object is in front of the mirror.

10. REFLECTION OF LIGHT PERISCOPE is created based on light reflection. It is used for submarine crews to view objects on land/surface when the submarine is submerged. Two plane mirrors are used to reflect and change the direction of light.

11. REFLECTION OF LIGHT KALEIDOSCOPE is created based on light reflection. It helps graphic designers in creating new patterns/motifs. Three plane mirrors are set at 60◦angles to one another. When the images overlap, interesting patterns/motifs can be viewed.

12. REFLECTION OF LIGHT A CONCAVE MIRROR has a smooth surface which is curved inwards. The image formed is: • Virtual, Upright & Magnified if the object is close to the mirror or • Real (able to be captured by the screen) & Inverted if the object is far from the mirror.

13. REFLECTION OF LIGHT A CONCAVE MIRROR is used: • In microscopes to reflect light to the objective lens; • By dentist to magnify the image of patients’ teeth; • In headlights of vehicles to produce a parallel beam of reflected light from a small bulb;

14. REFLECTION OF LIGHT A CONVEX MIRROR has a smooth surface which is curved outwards. The image formed is: • Virtual (not able to captured by the screen); • Upright; • Smaller than the object.

15. REFLECTION OF LIGHT A CONVEX MIRRORS have a large field of view; allow many things to be viewed at once. They are use in: • Security mirrors in shops • Blind corner mirrors to help drivers see objects around a corner.

16. REFRACTION OF LIGHT Refraction of light is the bending of light. When light travels from one transparent medium to another which is of a different density, it changes direction/speed as it travels through different transparent materials. In general :- • Slower in more dense materials; • Faster in less dense materials.

17. REFRACTION OF LIGHT Refraction has tricked our sense of sight in many ways. • A pool looks shallower than it really is • A straw looks bent in a glass of water • The stars in the sky appear further than they really are

18. DEFECTS of VISION & WAYS to CORRECT BLINDNESS A condition in which the eyes • Cannot detect any light at all or • The brain fails to receive or interpret nerve impulses from the eyes. • It can be caused by • Birth defects in the eyes • Serious injuries to the eyes • The cornea turning opaque • Serious injuries to the optic nerves

19. DEFECTS of VISION & WAYS to CORRECT COLOUR-BLINDNESS A condition in which the eyes cannot differentiate certain colours especially red and green. It is caused by the lack of certain photoreceptor cells in the retina which detect certain colours.

20. DEFECTS of VISION & WAYS to CORRECT COLOUR-BLINDNESS • Till now, there is no proven method to correct this problem. But most people with colour-blindness cope well with their deficiencies. How???

21. DEFECTS of VISION & WAYS to CORRECT ASTIGMATISM It happens when cornea loses its smooth curved shape, causing light rays that enter the eye fall on different spots, instead of being focused to a certain spot on retina. As a result, the image formed is blurred.

22. DEFECTS of VISION & WAYS to CORRECT ASTIGMATISM It can be corrected with cylindrical lens & through surgery.

23. DEFECTS of VISION & WAYS to CORRECT

24. DEFECTS of VISION & WAYS to CORRECT

25. LIMITATIONS of SIGHT OPTICAL ILLUSION Is a phenomenon in which something that we see is different in reality. This happens when brain fails to interpret the messages from the eyes correctly.

26. LIMITATIONS of SIGHT OPTICAL ILLUSION Is very useful especially to fashion designer. How??

27. LIMITATIONS of SIGHT BLIND SPOT Is a spot on the retina where the optic nerves leave the eye. It has no photoreceptors. Hence blind spot cannot detect any image on it.

28. TYPES OF VISION STEREOSCOPIC Both eyes are looking at the same object. But each eye has its own field of vision. • MONOCULAR • Each eye is positioned at each side of the head and does not look at the same object.

29. DEVICES to OVERCOME LIMITATION of SIGHT